GB2416589A - Gas sampling device - Google Patents

Abstract

A gas sampling device is in the form a bag 1 having a central seal 9 defining first and second chambers 3, 5. Each chamber 3, 5 has a respective inlet 15, 17 incorporating a one-way valve 19, 21. An indicator 25 is mounted on the interior surface of the bag 1, extending from the first chamber 3 across the seal 9 to the second chamber 5 in the region of a transparent window 23. The indicator 25 is curcumin and has a first portion A associated with the first chamber 3 which may come into contact with a gas collected in the chamber 3, a second reference portion B in the region of the seal 9, and a third portion C which may contact a gas collected in the second chamber 5. In use, breath samples are collected in chambers 3 and 5. The colour of indicator portions A and C may be compared to reference portion B to determine whether a difference in the amounts of ammonia present in the two samples exists. The device may be used to test for H. Pylori infection in a patient.

Description

241 6589 Gas Sampling Device The present invention relates to a device for

and a method of testing for the presence of a substance in samples of gas. The invention is particularly, although not exclusively suitable for detecting the presence of ammonia in gaseous samples The invention has general utility in detecting substances in gaseous samples, but is particularly, although not exclusively, applicable to a device for and a method of testing for the presence of a substance in samples of gas exhaled by a person. In certain embodiments the invention may be used to detect ammonia in the breath of patients suffering from Helicobacter pylori infection.

Testing of a gas sample is often carried out to determine whether a substance of interest is present in the gas. The gas sample may, for example, be taken from an environment, such as a confined space, and tested to determine whether a potentially hazardous substance is present, or to monitor a condition of the environment. Gas sampling is also often carried out in a clinical context, as a non- invasive diagnostic tool. A sample of gas exhaled by a person may be tested for the presence of a substance known to indicate a particular underlying condition.

A device for sampling a breath sample is shown in EP 1149557 A2 EP 1149557 A2 discloses a sampling device in the form of an inflatable bag into which a patient exhales to provide a breath sample The device incorporates an indicator, which is arranged to contact a breath sample collected in the bag. The indicator changes colour when a given substance to be detected is present in the sample thereby providing a visible indication as to its presence.

The applicants have realised that known gas sampling devices suffer from certain drawbacks, and the present invention therefore seeks to provide an improved sampling device which may more accurately and simply provide an indication as to whether a substance is present in a sample. In particular, the present invention is directed to the problem of providing a gas sampling device which allows a difference in the amounts of a substance present in more than one sample to be more easily determined According to a first aspect of the present invention there is provided: a gas sampling device; the device comprising a first chamber having an inlet for collecting a first sample of gas; and a second chamber having an inlet for collecting a second sample of gas; the first and second chambers each comprising an indicator for providing a detectable indication when a substance to be detected is present in a gas sample collected in the respective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance whereby a difference in the amounts of a substance present in gas samples collected in the first and second chambers may be detected The present invention therefore provides a gas sampling device having separate first and second chambers for collecting different samples of gas. An indicator is associated with each chamber for providing a detectable indication when a substance to be detected is present in a sample of gas collected in the chamber.

The indicators associated with each of the chambers are responsive to the same substance to be detected, thus allowing a difference in the amount of the same substance present in first and second samples of gas collected in the respective chambers to be determined.

It will be appreciated that the device of the present invention may be used to provide a simple positive or negative result as to whether a substance to be detected is present in either of the gas samples collected. However, in contrast to conventional single chamber devices, the dual chamber device of the present invention allows the amount of a substance present in the first chamber relative to that in the second chamber to be compared. Previously, to determine a difference in the amounts of a substance present in two samples has required the use of more than one gas sampling device to separately test the two samples. This is undesirable from an economical and environmental perspective.

Furthermore, the results obtained by each device must then be compared to assess the difference in the levels of a substance present. This may not be straightforward, and inherent differences in the response of each device may render results unreliable In contrast, by providing a single device having more than one chamber for testing multiple samples of gas, the present invention may provide a device which allows a difference in the amounts of a substance to be quickly and easily assessed, by comparison of the states of the indicators associated with the respective chambers.

The device of the present invention may be used to detect a change in general environmental conditions. For example, samples of a gas collected from a particular area at different times may be collected in the respective first and second chambers, to determine whether there has been a change in the amount of the substance present in the area. In a clinical context, breath samples may be collected 3 - from a patient at different times to monitor a change in the amount of a substance present in the breath as an aid in diagnosing or monitoring a condition. In other cases, the first and second samples may be collected from different places, for example different areas, or parts of an area in which the build-up of a potentially hazardous substance is being monitored. In clinical applications, the samples may be breath samples from different persons, allowing the presence of a given substance in the breath of those persons to be compared.

The present invention may provide a simple and effective way to determine whether a quantity of particular substance in a gaseous sample exceeds a threshold value. For example, a gas sample having a "safe" level of a particular potentially hazardous substance may be collected in the first chamber, and a second sample of gas taken from another region collected in the second chamber. The state of the indicator associated with the second chamber may then be compared to that associated with the first to determine whether or not the level of the substance in the second region exceeds the "safe" threshold level.

It will be appreciated that by providing more than one chamber for collecting a plurality of samples of gas, the present invention may provide a device having an in-built "control". For example, in the "threshold" determining context described above, the device may provide a more accurate and reliable result than would be obtained by taking a single sample of gas, and comparing the result to e.g. a reference colour indicative of the "safe" level. A number of factors may interfere with the response of an indicator, for example, other substances present in the gas, environmental conditions, manufacturing tolerances etc., increasing the risk of a "false positive" result. By taking two samples of gas in accordance with the present invention, the effects of such interference become less relevant, as a relative difference in the response indicators associated with the first and second chambers may be independent of such factors.

The device of the present invention is particularly useful in a clinical context.

Often a substance, which is indicative of an underlying condition, may naturally be produced by the body of a healthy patient by certain mechanisms, or may be produced due to diseases unrelated to that being investigated. To avoid a false positive result being obtained, a patient may be administered with an activator to promote production of the substance by means of a mechanism which will only occur if the patient has a particular condition By collecting samples of breath in the first and second chambers before and after administration of such an activator, the present invention provides a way to easily detect whether a difference in the production of the substance has occurred as a result of the administration of the activator, leading to an increased level of production of a given substance relative to the "natural" or "baseline" level present in the body, indicating the presence of the condition being investigated.

The applicants have found that the present invention may allow a difference in the amounts of a substance present in the first and second samples of gas to be more reliably detected than a single chamber device allows, even for relatively small differences This is because the human eye may be more sensitive to assessing a difference in the appearance of the indicators associated with the chambers, than to judging an absolute state of a single indicator. The respective indicators may be located in relatively close proximity to one another in accordance with the invention allowing a direct comparison to be made.

It will be appreciated that the invention may allow testing for a difference in the amounts present of a substance in plural gas samples by simple visual I S observation by the human eye under ambient conditions, and without the need to use more complex electronic or optical equipment. The gas sampling device may therefore be used in contexts where access to such equipment is not readily available, e.g. in remote areas, or where an instant result is required The device may be used to provide a final result, or to identify situations which require further investigation using more sophisticated apparatus As the device allows a result to be determined by comparison of the states of the indicators associated with the first and second chambers, a greater number of indicators may potentially be used than in a conventional single chamber device, in which an absolute change of state of the indicator must be detemmined For example, an indicator which does not exhibit a significant change in colour on detection of a substance may be suitable for use in accordance with the invention, as a user may more easily discern a small change in e. g. colour of an indicator by reference to the "in-built" reference which the indicator associated with the other chamber provides.

As results are based upon detection of a relative change in the states of the indicators, indicators, which are not selective in responding only to a particular substance whose present is to be detected, may be used.

In accordance with the present invention, the first and second gas samples may be taken from any gas or gases which it is desired to test for the presence of a substance. For example, as discussed above, the gas may be taken from an environment, such as a confined space, in order to test for the presence of a potentially hazardous substance. However, the present invention provides a gas - s sampling device which is particularly suitable for use in a clinical context.

Preferably, therefore, the gas samples are samples of gas exhaled by a person i.e. breath samples The device may be used to provide a simple positive or negative result for the presence of a substance in each of the chambers which may be qualitative or quantitative. However, preferably the device is used to determine a difference in the amounts of a substance present in gas samples collected in the first and second chambers. It will be appreciated that the difference may be zero in cases in which the same amount of a substance to be detected is found to be present within each chamber to the level of sensitivity that the indicators associated with each chamber allow.

The present invention extends to a method for detecting a difference in the amount of a substance present in first and second gas samples using a device in accordance with the invention Thus, in accordance with a further aspect of the invention there is provided a method for detecting a difference in the amounts of a substance present in first and second gas samples using a gas sampling device comprising; a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas, the first and second chambers each comprising an indicator for providing a detectable indication when a substance to be detected is present in a gas sample collected in the respective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance; the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in the second chamber, and comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second samples of gas to determine a difference in the amounts of a substance to be detected present in the first and second gas samples.

As discussed above, the device may be used to compare the amount of a substance present in gas samples taken from different areas, or in breath samples taken from different persons. However, the device is particularly suitable for monitoring a change in the amount of a substance present over time. Preferably the gas samples collected in the first and second chambers are derived from the same source at different times. For example, the gas samples may be taken in an environment in which it is desired to monitor the build-up of a particular substance over time. In a clinical context, the samples collected are preferably samples of the breath of a person before and after administration of an activator which promotes the production of a given substance by a mechanism indicative of an underlying condition. In this way, the first chamber may act as control, reducing the likelihood of a false positive result being obtained due to the presence of the substance in the breath for other reasons, such as natural fluctuations or other unrelated conditions.

The gas sampling device and the first and second chambers may be of any suitable size For example, the size may depend upon factors such as the volume of the first and second gas samples required to produce a response in a given indicator, or to provide a representative sample of the gas, and factors such as the environment in which the device is intended to be used or stored. The volume of each chamber in the gas sampling device may range from a few cm3 to as great as 50 1itres for certain applications. For example, for breath testing devices each chamber may have a volume in the range of from 10 to 500 cm3, and preferably from 100 cm3 to 200 cm3 Volumes in this range may provide a device of a size which may easily be manually handled, and can accommodate a sample of a size which may give rise to a reliable result The gas sampling device may be formed from any suitable material or materials which do not interfere with gas samples collected in the first and second chambers, or the indicators associated with the respective chambers, in a way which might affect results. For example, the material should not contain any e.g. additives which might render the indicator inoperative, provide a "false positive" result or impede sample gases from coming into contact with the indicators as described below.

The gas sampling device need not necessarily prevent the passage of gas between the exterior of the device and the interior of the first and second chambers, provided that the rate at which gas may flow between the interior and exterior of the device is sufficiently low that the amount of gas which may move between the interior and exterior of the device is not great enough to affect the results obtained once samples have been collected and before the indicator exhibits any response.

However, in preferred embodiments the gas sampling device prevents the passage of gas between the interior of the first and second chambers and the exterior of the device.

The gas sampling device may be sealed in a container which prevents the entry or exit of gases to or from the interior of the chambers once a result has been obtained. In this way, a controlled environment may be produced for storing the device for later analysis, e.g. by a more sensitive device to provide a quantitative result for the amount of a substance present, or to allow its transport while preserving the result obtained. This may be particularly appropriate when the gas sampling device does not provide a gas impervious barrier preventing the passage of gas between the interior and the exterior of the device.

Preferably the device comprises paper and/or plastics materials The use of such materials may provide an economical device which is suitable for disposal after a single use. Suitable plastics materials include polymeric materials such as nylon, PVC or polyethylene. Preferably the plastics material is a polymeric film Suitable paper materials include any cellulosic sheet materials, such as nitrocellulose The gas sampling device may comprise a single material, or may comprise a combination of materials, such as a laminate of more than one layer of the same or different materials. In some preferred embodiments the device comprises a laminate of a paper and polymeric film.

It will be appreciated that the properties of the materials, e.g thickness, basis weight etc. should be chosen as appropriate with regard to the environmental conditions which the device must withstand in use. For example, the device should retain its integrity over the temperature and pressure ranges likely to be encountered, and over timescales from the collection of samples to the analysis of results, and over any period that the device may subsequently be stored The present invention may advantageously provide a gas sampling device which is disposable after a single use. Preferably the device is disposable according to standard procedures, particularly those used for the disposal of medical products such as incineration or burial, without presenting a hazard to the environment. For example, preferably the device may be incinerated without producing potentially hazardous by-products or residue. Preferably, the device is biodegradable. By "biodegradable" it is meant that all components of the device readily break down after disposal over time without presenting a significant hazard to the environment, or leaving a residue which may be potentially harmful to the environment.

The first and second chambers may be constructed as appropriate for collecting samples of gas. For example, the chambers may be initially evacuated, to allow them to receive a gas sample. This may be appropriate if the device is formed from a relatively rigid material. However, preferably, the first and second chambers are inflatable. It will be appreciated that in these preferred embodiments the first and second chambers should be independently inflatable. This arrangement provides a simpler device which may occupy a relatively small amount of space when stored prior to use. Preferably the device is flat in its deflated configuration.

For example, the device may be in the form of a flat bag.

It will be appreciated that the device need not prevent the communication of gas between the first and second chambers, provided that any such communication occurs at a sufficiently low rate relative to the time required for the indicators associated with the chambers to provide a response, such that results are not affected to a significant degree relative to the level of sensitivity the device provides Thus the device should maintain the composition of the gas samples in each chamber constant at least over the period between collection and taking of results to the level which may be detected given the sensitivity of the device.

Preferably the gas sampling device does not allow communication of gas between the first and second chambers This may ensure that samples of gas collected in the first and second chambers are maintained separate, avoiding the risk of gas moving between the first and second samples which may otherwise interfere the response of the indicators associated with the chambers. Preferably, the first chamber is separated from the second chamber by a gas impervious barrier The barrier may be provided in any suitable manner. For example, the barrier may be provided by a separate component or integrally formed with the first and second chambers. For example, the barrier may be an internal wall or bond line which divides the interior of the gas sampling device into first and second chambers In other embodiments, the first and second chambers may be separate containers, whose walls provide a gas impervious barrier separating the chambers The first and second chambers may share an interface For example, the gas sampling device may define a single enclosed space divided into a plurality of chambers Preferably, however, the first chamber is separated from the second chamber by a bond line. The bond line may be e.g. an adhesive bond line, or a thermal or ultrasonic bond line. The bond line may then act to seal gas in the first chamber from gas in the second chamber. In a particularly preferred embodiment, the gas sampling device comprises first and second sheets of heat fusible plastics material selectively thermally bonded to one another to provide first and second chambers.

In other embodiments the first and second chambers are separate containers which do not share an interface. Thus in these embodiments the first and second chambers are preferably not attached to one another along their length The containers may be spaced from one another. Preferably the containers are attached to a common mounting plate. In embodiments where the first and second chambers - 9 - are joined to a mounting plate, the mounting plate preferably extends across an open end of each of the first and second chambers. As described below, the indicators associated with each chamber may then advantageously be attached to the mounting plate in a region which may contact gas samples collected in the interior of each chamber In other arrangements, the mounting plate may be attached to sidewalls of the first and second chambers The first and second chambers may be of any shape in their deflated and inflated configurations. Por example, the chambers may be of a regular shape such as square, rectangular, cylindrical, or an irregular shape when inflated. In some embodiments, the chambers are flat in their deflated configuration. Por example, the gas sampling device may be in the form of a flat bag whose interior is divided into a plurality of chambers. In other embodiments, the first and second chambers may extend from a deflated configuration as gas is collected. This may be appropriate in embodiments where the first and second chambers are provided by separate containers. Por example, the chambers may extend as they inflate from a coiled deflated configuration, or may extend in a concertina-like manner from a deflated configuration. The chambers may be provided with formations such as corrugations to facilitate their expansion as gas enters the chamber The first and second chambers may be arranged as desired. In some embodiments the first and second chambers are arranged in side-by-side configuration In these embodiments, the first and second chambers may be substantially parallel to one another when inflated In other embodiments, the first and second chambers may be arranged in end-to-end configuration. These embodiments may be appropriate if the first and second chambers are defined by separate containers The chambers may then extend away from one another as they inflate Preferably, the first and second chambers do not overlap one another when in their inflated configuration. This may allow a visible change in the indicators associated with each chamber to be more clearly detected, particularly when the first and second chambers are formed from a material incorporating an indicator, or the indicator is provided on a surface of one or both of the chambers.

Each of the first and second chambers comprises an inlet along which gas may flow into the chamber to provide the first and second samples of gas. The inlets may be arranged in any manner, provided that separate samples of gas are directed into each of the chambers. Gas flowing into the first and second chambers may share a pathway for a part of its path from the exterior of the device into the first or second chamber. For example, the device may be provided with a single inlet to its interior, which then divides within the device to provide separate inlets to the first and second chambers. For example, a valve arrangement may be used to direct the first part of a quantity of gas entering the device into the first chamber.

The valve may then close once a predetermined quantity of gas has entered the first chamber, diverting any further gas entering the device towards the second chamber.

However, in preferred embodiments, gas flows along separate paths from the exterior of the device to interior of the first and second chambers. Preferably, therefore, separate inlets are provided between the exterior of the gas sampling device and the interior of the first and second chambers. This arrangement may further reduce the likelihood of contamination between the first and second samples which may otherwise interfere with results In embodiments where the first and second chambers are attached to a mounting plate the inlets are preferably provided on the mounting plate.

The inlets may be configured as appropriate, depending upon the manner in which gas is to be introduced to the device. For example, the inlets may be configured to receive a gas delivery device, such as a syringe or a straw. In preferred embodiments, the gas sampling device is a breath sampling device, and the inlets to the first and second chambers are configured as mouthpieces The inlets may be closed in any suitable manner once the respective first and second samples of gas have been received in the first and second chambers. For example, the inlets may be provided with closures, such as plugs or screw- fitted tops, which may be applied by a user once a sample has been collected in the chamber. Preferably the first and second inlets comprise one-way valves which inhibit the passage of gas out of the first and second chambers. The valves may then allow the passage of gas into the first and second chambers to allow collection of a sample, but seal the chamber once a sample of gas has been obtained, preventing the movement of gas out of the chamber through the inlet. The valves may be configured to open only when a flow rate of gas towards the interior of the first and second chambers exceeds a predetermined amount thereby inhibiting the passage of gas from the exterior of the device into the interior of the first and second chambers at times other than when a gas sample is being collected. In this way, the possibility of contamination of samples in the first or second chambers may be reduced The indicators associated with the first and second chambers may comprise any substance or substances which provide a detectable indication of the presence of a given substance which it is intended to detect in a gas sample contained in the associated chamber.

It will be appreciated that the indicators associated with the first and second chambers need not comprise the same indicator substance provided that they are responsive to the same substance to be detected. Thus it should be understood that different indicators having any or all of the features discussed below may be associated with the first and second chambers. References to the "indicator" below therefore refer to the indicator or part of the indicator associated with either the first or the second chamber. The indicator or part thereof associated with the other chamber need not necessarily be identical e.g. in composition and configuration.

However, preferably the same indicator substance is associated with the first and second chambers. In this way, errors, which might otherwise be introduced due to differences in the responses of different indicator substances associated with the first and second chambers in the presence of the substance to be detected, may be avoided.

The detectable indication may be a change in the state of the indicator, such as a change of colour and/or intensity, which change may lie in thepart of the electromagnetic spectrum which is visible or invisible to the unaided human eye.

The indication may be thus detectable only with the use of additional optical or electro-optic equipment or under particular illumination conditions. The indication may be detectable e.g. in the form of an emission or absorption peak. The indication may be displayed graphically or in the form of a digital result. For example, the indication may be a change in the colour or intensity of an emission such as a fluorescence emission, which change is of a wavelength, which does not lie in the portion of the electromagnetic spectrum visible to the naked human eye. The indication may then be detectable only with the assistance of optical or electro-optic equipment, such as a spectrophotometer. A suitable detection apparatus might consist of a light source illuminating the indicator, and an optical detector and associated electronics for processing and displaying the result (e.g a spectrophotometer). For example, certain suitable indicating substances exhibit changes which occur predominantly in the near infrared part of the spectrum. Such changes may or may not be accompanied by a change within the visible part of the electromagnetic spectrum. Thus for such indicators a near infrared spectrometer may be used to detect a change in the state of the indicator, or to verify a change observable visually.

Preferably the indicator provides a visible indication which is observable from the exterior of the device when a substance to be detected is present in the sample However, as discussed above, the invention provides a particularly simple way for a difference in the amounts of a substance present in the first or second chambers to be detected visually by comparison of the states of the indicators associated with the respective chambers. Preferably the detectable indication is a visible indication.

In accordance with a further aspect the invention provides a gas sampling device; the device comprising a first chamber having an inlet for collecting a first sample of gas; and a second chamber having an inlet for collecting a second sample of gas; the first and second chambers each comprising an indicator for providing a visible indication when a substance to be detected is present in a gas sample collected in the respective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance whereby a difference in the amounts of a substance present in gas samples collected in the first and second chambers may be detected.

In accordance with yet another aspect of the present invention there is provided a method for detecting a difference in the amounts of a substance present in first and second gas samples using a gas sampling device comprising; a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas, the first and second chambers each comprising an indicator for providing a visible indication when a substance to be detected is present in a gas sample collected in the respective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance to be detected, the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in the second chamber, and visually comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second samples of gas to determine a difference in the amounts of a substance to be detected present in the first and second gas samples.

The visible indication may be a change in the state of the indicator such as a change of colour and/or intensity The visible indication may be visually detectable only with the use of additional optical or electrooptic equipment or under particular illumination conditions. For example, the visible indication may be an indication which is detectable by the human eye only when the indicator is viewed through a filter, or illuminated with a particular wavelength of light Preferably the visible indication is detectable by the unaided human eye, and preferably under ambient conditions.

It will be appreciated that the indicator may exhibit a primary change which is visually detectable, and also a secondary change in response to the presence of a substance to be detected which is not visible to the aided or unaided human eye.

The visible change may then be used to provide a rapid assessment as to the presence of a substance in the chamber, with the device then being subjected to further analysis to verify and/or quantify the visual change observed using appropriate equipment capable of detecting the secondary non-visible change.

For example, certain substances may exhibit a colour change in response to the presence of a substance to be detected which change is just visible to the human eye, and which may be used as a primary indication of the presence of the substance.

The same substance may also exhibit a strong absorption peak in a part of the spectrum, such as the near infrared, which may be detected using e.g. a spectrophotometer as a secondary indication of the presence of the substance to be detected. it is known that some polymeric substances behave in this way.

In some embodiments primary indicators may be provided associated with each chamber for providing a visible indication when a substance to be detected is present in a sample of gas collected in the chamber, and secondary indicators may be provided associated with each of the chambers for providing a non-visible indication when a substance to be detected is present in the respective chambers The primary indicators may then provide a quick determination as to the amounts of a substance present in the chambers by simple visual observation, with or without the use of appropriate illumination filters, etc. However, preferably the primary visible indication is detectable by the unaided human eye, and preferably under ambient conditions. This result may then be verified and/or quantified by analysing the secondary indicators using appropriate equipment, e.g. a spectrophotometer. For example, the secondary indicator may be analysed in cases where the primary indicator result is borderline. The primary and secondary indicators may the same or different substances.

The gas sampling device may provide a system which merely indicates the presence or absence of a substance to be detected in the first and second gaseous samples, but preferably allows a relative difference in the amounts of the substance present in the two samples to be measured. Preferably the indicator thus exhibits a detectable change in response to an increase in the amount of the substance to be detected being present in a gaseous sample For example, the change may be a change in shade or in intensity. Preferably the indicator exhibits an increase in intensity of a colour change in response to an increase in the amount of the substance to be detected being present in a sample.

If the device is to be used only to detect a relative difference between the amounts of a substance present in the two samples, a wider range of indicators may be used. For example, in arrangements where the detectable change is a visible change it is possible to use indicators which do not exhibit a significant detectable change in response to differing amounts of a substance being present in the samples, as it has been found that it is easier for the human eye to detect a difference in e.g colour or intensity between two indicators than to judge a colour change against an absolute reference, e.g. denoting a particular quantity of a substance, or its presence/absence. It is also not necessary to ensure that the indicator used is selective in responding only to the substance which is to be detected If the indicator 1 S exhibits a change in response to other substances, the substances will generally be present in both of the samples taken, and therefore not affect the relative difference detected.

Preferably the indicator comprises a natural substance, such as a plant extract. The use of indicators of this type may provide a device which may be disposed of without hazard to the environment, and which presents a lower risk when used in a clinical context The indicator substance may be provided in combination with a suitable carrier, excipient and the like, or with other substances which do not interfere with the ability of the indicator to exhibit a visible change on the presence of the substance to be detected The indicator substance should be selected as appropriate with respect to the substance which is to be detected. Indicator substances providing a detectable change in response to the presence of a wide range of substances to be detected in gaseous samples are known. Many such indicator substances provide a visible change such as a colour change in response to a change in the pH of a solution to which the indicator has been added Indicators of this kind may be e.g. impregnated in a suitable carrier, e.g. litmus paper, which may indicate whether a solution applied to it is acidic or alkaline and thus whether the solution contains a particular substance. Examples of such indicators include methyl orange, phenolphthalein and thymol blue.

If the indicator acts on the basis of a change in the pH of a solution which it contacts, it will be appreciated that the indicator may need to be moistened in order to obtain a response, for example if the gas sample collected in the first or second chamber does not have a sufficiently high moisture content to provide a medium in which a substance to be detected may dissolve. This might be achieved by moistening the indicator substance during manufacture, or may be carried out subsequently by a user. For example, a user may introduce a small quantity of distilled water through the inlet into the respective chamber. In other arrangements, the device may comprise a separate inlet or inlets associated with the indicator to allow moisture to be supplied to the indicator. For example, a flap may be provided in the surface of the device. In yet other arrangements, the device may comprise a quantity of water in a sealed compartment, which compartment may be burst by a user to allow the water to come into contact with the indicator. Alternatively, or additionally, the indicator may be conditioned by supplying a gas sample of relatively high humidity to the chamber to moisten the indicator associated with it prior to collection of a gas sample to be analysed. The "conditioning" sample may then be exhausted from the device once the indicator has been suitably moistened to allow a gas sample of interest to be collected and analysed.

Other indicating substances are known which exhibit a detectable change on detection of a substance, and which do not operate on the basis of detecting a change in pH. Such indicators may be used for detecting substances which do not exhibit a significant change in pH, or may be suitable for use where levels of moisture are low. indicators which do not act on the basis of a change in the pH of a solution, do not necessarily require the indicator substance to be in an aqueous solution.

Examples of such indicators include curcumin, or indicators operating on the basis of pyridine-pyrazolone or indophenol reactions.

Other groups of indicators include triphenyl methanes, polymethines, acridines and cyane dyes. On interaction with an acid or base, e.g. a substance to be detected, the polyene system of these indicators changes in length. This change in length results in a change in the absorption wavelength of the system, and hence is detectable as a change in an emission or absorption peak of the system The change in absorption wavelength may result in a visible change such as a colour change, directly or indirectly observable by the human eye, or may be detectable only with the aid of optical or electro-optical equipment It will be appreciated that the indicator may not necessarily be a dye, exhibiting a change in the visible part of the spectrum.

In clinical applications, the device may be used to test breath samples to aid in diagnosis of medical conditions such as breast or lung cancers, rejection of transplanted organs, such as the heart, or pulmonary conditions such as tuberculosis.

In these cases, an indicator which exhibits a detectable, preferably visible indication in response to the presence of volatile organic substances in a breath sample may be used, as the presence of such substances may be indicative of these underlying conditions. In other applications, the device may comprise an indicator substance responsive to the presence of volatile sulphur compounds or gases, such as hydrogen sulphide, methylmercaptan, polysulphides, organic sulphides and some thiols. The presence of these substances in a breath sample may indicate the presence of diseases such as hepatic coma or halitosis, either oral or non-oral.

In a particularly preferred embodiment, the gas sampling device is used to test for the presence of ammonia in the first and second gas samples It is known that ammonia may build up in confined spaces to potentially hazardous levels This problem is particularly significant in confined spaces such as livestock sheds, where animal waste products may lead to unpleasant and hazardous levels of ammonia in the atmosphere, see for example Iowa Concentrated Animal Feeding Operation Air Quality Study Report, Environmental Health Sciences Research Centre, University of Iowa (2002), in particular Chapter 6 2, pp 115-120, which mentions studies suggesting that exposure to ammonia can decrease the resistance of livestock to infection as well as affecting their growth. It is also often desirable to monitor the build up of ammonia in the atmosphere of food production facilities, where low levels of ammonia can lead to undesirable contamination or spoiling of food Preferably the indicators associated with the first and second chambers of the device exhibit a detectable change in response to the presence of ammonia in a gas sample collected in the chamber. In these preferred embodiments the device of the present invention may provide a simple and inexpensive way of e.g. monitoring the build up of ammonia in such areas, by taking first and second gas samples from the area at different times, or comparing levels of ammonia in samples taken from different areas, or comparing the level of ammonia in a sample taken against a sample having a threshold "safe" level of the substance.

In accordance with a further aspect of the present invention there is provided a device for the detection of ammonia in first and second gas samples, which device comprises a first chamber having an inlet for collecting a first gas sample; a second chamber having an inlet for collecting a second gas sample; the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a gas sample collected in the chamber, whereby a difference in the amounts of ammonia present in gas samples collected in the first and second chambers may be detected In accordance with a further aspect of the invention there is provided a method for detecting a difference in the amounts of ammonia present in first and second gas samples using a gas sampling device comprising; a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas, the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a gas sample collected in the respective chamber, the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in a second chamber, and comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second samples of gas to determine a difference in the amount of ammonia present in the first and second gas samples In these applications, the detectable indication is preferably a visible indication, and preferably a visible indication which may be observed by the unaided human eye. The device may then provide a particularly simple way to obtain a quick initial diagnosis by direct visual comparison of the first and second indicators without the need to use additional equipment, or subject the device to further analysis. The device may therefore allow at least initial diagnosis to be performed without the need for a person to attend a medical centre having sophisticated equipment, or highly skilled personnel.

In a clinical context, it has been found that ammonia present in a breath sample may be indicative of the presence of the H. Pylori bacterial infection It is now widely accepted that bacterial infection by H. Pylori, discovered approximately 20 years ago, leads to peptic ulcers that affect around I in 10 people at some time in their lives, with many more suffering from gastritis. The bacteria are quite common, but the extent of infection in the population is not known exactly.

Estimates vary between 10% of population in the developed countries to 60% of the population in the developing countries. For example, it is known that 25 million Americans currently suffer from ulcers, with 350, 000 to 500,000 new cases and more than 1,000,000 ulcer-related hospitalizations occurring annually Treatment places a large burden on health services.

Currently, both invasive and non-invasive methods exist to screen for H. Pylori infection. Invasive methods include histology, culture tests and the urea test on gastric fluids. Non-invasive screening for these bacteria may be carried out using breath samples, often collected in a doctor's surgery and sent for analysis in an outside laboratory There is a need for a simple and cost-effective method of screening for Helicobacter Pylori infection.

Commonly used Carbon'3 and Carbon'4 non-invasive tests for diagnosing H. Pylori infection involve a patient providing a breath sample in order to determine a base level of carbon'3 dioxide or carbon'4 dioxide ('3CO2 or '4CO2) present in the exhaled breath, due to "normal" causes due to ingestion of certain foods.

The patient is then administered an activating substance, TIC- or '4Clabelled urea, and, after a suitable period has elapsed to allow the ingested urea time to contact any H. Pylori in the gastro intestinal tract, a second breath sample is taken, and tested for the presence of SCOT or 14CO2. H. Pylori excretes an enzyme, urease, which catalyses the breakdown of urea into ammonia and carbon dioxide, and which, under normal circumstances, is not present in the human body. If a patient is infected with H. Pylori bacteria, the second sample obtained after ingestion of the urea would be expected to exhibit a greater quantity of '3CO2 or SCOT than the first or "control" sample taken to establish the base level of '3CO2 or '4CO2 in the patient's body.

A newer test for H.Pylori infection is based on the detection of ammonia breath in the samples supplied by the patient, rather than '3CO2 or '4CO2. In a similar way to the '3CO2 or SCOT test, a patient provides breath sample in order to determine a base level of ammonia present in the exhaled breath, due to "normal" causes due to ingestion of certain foods, or due to other conditions, unrelated to H. Pylori infection, such as renal failure or certain oral and dental conditions which may result in ammonia production.

The patient is then administered an activating substance, e.g ordinary unlabelled urea, and, after a suitable period has elapsed to allow the ingested urea time to contact any H. Pylori in the gastro intestinal tract, a second breath sample is taken, and tested for the presence of ammonia. If a patient is infected with H. Pylori bacteria, the second sample obtained after ingestion of the activating substance would be expected to exhibit a greater quantity of ammonia than the first or "control" sample taken to establish the base level of ammonia in the patient's body.

It will be seen that in embodiments where the indicators associated with the first and second chambers are responsive to the presence of ammonia in gas samples in those chambers, the present invention may provide a simple and effective way of testing for H. Pylori infection by comparison of the states of the indicators associated with first and second chambers of the device, in which breath samples have been collected corresponding to the breath of the patient before and after ingestion of urea. Preferably the detectable indication is visually detectable.

In contrast to when conventional breath sampling devices are used, it has been found that it is not necessary to label the urea with 14C or 13C when testing breath samples for ammonia using the dual chamber gas sampling device of the present invention. A test may be carried out e.g. in a doctor's surgery, allowing a quick and reliable diagnosis to be made by simple visual observation, and without the need to send samples away for analysis, or to use any electronic or optical 1 0 equipment.

In accordance with a further aspect of the present invention there is provided a device for the detection of ammonia in samples of breath exhaled by a person, which device comprises a first chamber having an inlet for collecting a first breath sample; a second chamber having an inlet for collecting a second breath sample; the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a breath sample collected in the chamber, thereby allowing a difference in an amounts of ammonia present in breath samples collected in the first and second chambers to be detected.

In accordance with a further aspect of the invention there is provided a method for detecting a difference in the amounts of ammonia present in first and second breath samples using a breath sampling device comprising; a first chamber having an inlet for collecting a first breath sample, and a second chamber having an inlet for collecting a second breath sample, the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a breath sample collected in the respective chamber, the method comprising the steps of collecting a first breath sample in the first chamber, collecting a second breath sample in a second chamber, and comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second breath samples to determine a difference in the amounts of ammonia present in the first and second breath samples In accordance with a further aspect of the present invention there is provided a method of diagnosing H. Pylori infection using an ammonia detection device in accordance with the present invention The ammonia detection device of these further aspects of the invention may incorporate any or all of the features discussed in relation to the other aspects of the invention.

As well as allowing the detection of H. Pylori infection, the presence of ammonia in a breath sample may also indicate the presence of other disorders, such as renal dysfunction, hepatic dysfunction and genetic defects in urea production.

In the aspects and embodiments where the gas sampling device is an ammonia detection device, the indicators associated with the first and second chambers may be selected from any of a wide range of indicators known to exhibit a detectable, preferably visible, response in reaction to the presence of ammonia in a gaseous sample For example, the indicator may comprise a conventional indicator which changes colour in response to a change in pH, such as oxazene dyes, bromothymol blue, bromeocresol purple, bromocresol green, crystal violet, phenyl red, chresol red and malachite green. Other indicators which may be used to detect ammonia, are based on pyridine-pyrazolone or indophenol reactions. Phloxine, rose Bengal and bromophenyl blue are also suitable indicators for detecting ammonia by means of an acid-base mechanism Preferably the indicator comprises curcumin. Curcumin undergoes a colour change from yellow to red brown on exposure to gaseous ammonia. Curcumin ( 1,7 bis(4-hydroxy-3methoxyphenyl)-1,6-heptadien-3,5-dione) is a coloured compound belonging to the family of the curcuminoids and is the main compound responsible for the colour of turmeric. Curcumin is an orange-yellow crystalline powder which is insoluble in water, and consequently is not used as an indicator for aqueous acid/base reactions. It is also insoluble in ether, but soluble in ethanol and glacial acetic acid Turmeric is the dried and ground rhizome or bulbous root of curcuma longa, a herb of the Zingiberacae family native to Southern Asia and cultivated in China, India and the East Indies.

In comparison to other commonly used indicators for detecting the presence of ammonia, Curcumin is not significantly influenced by other substances commonly found in the atmosphere or in the breath of a patient. These gases include carbon dioxide, acetone, methanol, ethanol, dimethyl disulphide and acetic acid Although the collection of two gas samples in accordance with the present invention reduces the problems associated with interfering species experienced with single chamber devices, by using Curcumin the risk of false positive results may be further reduced It is known that Curcumin is a suitable for indicator detecting cyanide. Thus, Curcumin is not suitable for use in detecting ammonia in gaseous samples in which cyanide is also likely to be present. However, this is not a significant limitation in use, since cyanide is not commonly present in the atmosphere or in the breath.

As curcumin is present in the plant extract turmeric, which is widely and safely used for culinary purposes, curcumin is particularly suitable for use in providing indicators for use in clinical applications, as well as providing a gas sampling device which may present a lower hazard to the environment in use and on disposal The indicators associated with the first and second chambers in accordance with the invention in any of its aspects and embodiments may be provided in any manner that allows them to come into contact with a gas sample collected in the first or the second chamber. The indicator may be immobilised on a substrate that is porous to gases. Examples of suitable porous substrates include cellulosic materials such as paper, e.g. filter paper, nylon or nitrocellulose. Suitable solid materials such as sintered calcium phosphate may also be used The indicator may be immobilised on the substrate in any known manner, e g incorporated in the substrate so that it is present substantially uniformly throughout, or adsorbed or coated onto the outer surface of the substrate The substrate should have a large enough surface area to ensure sufficient contact between the gaseous sample and the indicator.

The indicator may be provided on a substrate attached to the device, or may be printed or coated onto a region of the device, or incorporated with the material from which the device is formed In a particularly preferred embodiment, the first and second chambers of the gas sampling device are formed from material which comprises an indicator. For example, the material from which the device is formed in the region of the first and second chambers may be impregnated with an indicator, or an indicating material may be applied to a surface or surfaces of a material in these regions during or after manufacture of the device. For example, an indicating material may be coated on to the device in the region of the first and second chambers, or a layer of indicating material laminated to the material of the device.

Alternatively the indicator may be a further layer or coating applied to the gas sampling device at least in the region of the first and second chambers after it has been manufactured.

The indicators associated with the first and second chambers may beprovided in a localized region or regions of the device associated with the respective chambers. In other embodiments, the indicator may cover the entire area of the chamber with which it is associated. In this way, a larger area may be provided which may exhibit a detectable change if a substance to be detected is present, which may be more readily detected by the user, particularly when the change is a visible change.

Although separate indicators associated with each chamber may be provided, preferably, a single indicator is provided which extends between the first and second S chambers having first and second portions associated with the first and second chambers. In this way, the same indicator substance may be associated with each chamber, allowing a more consistent response to the presence of the substance to be detected to be obtained by observing the states of the parts of the indicator associated with the respective chambers, and avoiding errors which might be introduced due to differences in the indicator associated with the first and second chambers.

Preferably the gas sampling device includes a reference sample of the indicator or indicators associated with the first and second chambers which is prevented from coming into contact with gas samples collected in the first and second chambers In this way, the state of the indicator associated with the first or second chamber may be compared to this reference sample to allow a change in the state of the indicator to be more easily detected. The reference may be provided by a separate sample of the indicator which is applied to the gas sampling device, for example on an exterior surface, or in the region of a seal, but preferably is a portion of the indicator associated with the first or second chamber. The reference may then be provided in closer proximity to the indicators associated with the first and second chambers allowing a user to more easily visually verify whether, and, if appropriate, the extent to which, a colour change has taken place in the parts of the indicator associated with the first and second chambers on exposure to the respective samples.

In preferred embodiments where a single indicator is provided having first and second portions associated with the first and second chambers for detecting the presence of a substance in respective gas samples collected in the chambers a reference portion is preferably provided between the first and second portions which does not come into contact with gas samples collected in the first or second chambers. In a particularly preferred embodiment, the indicator extends across a seal provided between the first and second chambers The part of the indicator located in the region of the seal is thus prevented from coming into contact with either of the first or second samples of gas.

Preferably means are provided to enhance the detectable indication in the indicator, particularly when the indication is a visible indication. In some preferred embodiments, the indicator is surrounded by a transparent window to enhance the visibility of a change exhibited by the indicator when the substance to be detected is present For example, the indicator may be mounted to a transparent patch attached to the gas sampling device, or the gas sampling device may comprise a transparent material in the region surrounding the indicator. The gas sampling device may be stiffened in the region of the indicator, e.g. by means of an additional layer, or thicker portion, to reduce the likelihood of surface undulations being present in the region of the indicator In embodiments in which the first and second chambers are attached to a mounting plate, the indicators associated with the respective chambers are preferably provided on the mounting plate. This may provide a surface free from surface undulations, enhancing the visibility of any change which occurs in the state of the indicator.

Although in embodiments where the indicators exhibit a visible change when a substance to be detected is present, the indicators preferably exhibit a visible change which may be observed visually under ambient conditions, the gas sampling device may incorporate a filter through which the indicator is viewed to allow a change in the state of the indicator to be visually detected by the human eye or to enhance the visibility of a change.

The device may be used to determine a simple qualitative difference in the amounts of the substance present in first and second samples, or may be used to obtain a quantitative result. A quantitative result may be obtained for example by comparing the colours of the indicators associated with the respective first and second chambers to a scale, linking colour intensity or shade to a quantitative amount of the substance to be detected being present. The device may therefore incorporate a scale allowing a quantitative value for the amount of the substance to be detected in the first and/or second gas samples to be derived from the observed state of the indicators. If the change is detected using electro-optical equipment, a qualitative result may be provided directly by the apparatus.

It will be appreciated that the present invention provides a simple and effective way for a difference in the amount of a substance present in the respective first and second gas samples to be determined preferably visually by the human eye, and without the need to use any additional e.g. processing equipment. However, the indicators associated with the first and second chambers may alternatively or additionally be subjected to further analysis to determine a more accurate quantitative value for the amounts of the substance to be detected in the chambers, or to verify results derived visually If the device includes primary and secondary indicators for providing visible and non-visible changes, the secondary indicator may be subjected to further analysis to verify and/or quantify results derived from visual inspection of the primary indicators.

Preferably the indicators associated with the first and second chambers are provided on a portion of the device which is severable from the first and second chambers. For example, this may be achieved by attaching the indicators to a mounting plate, where provided In this way, the indicators may be sent for further analysis or storage, without needing to retain the whole device, including the chambers in which the samples were collected, providing a more convenient and hygienic arrangement. In arrangements where the indicator is to be stored for subsequent analysis, and not just used to provide an instantaneous result, the indicator preferably exhibits a permanent and irreversible change in response to the presence of the substance to be detected, to avoid any further changes occurring, e.g. in response to environmental conditions at a later stage. Otherwise the indicator may be maintained in a controlled environment after it has exhibited an initial 1 5 change Depending upon the nature of the gas which is to be tested, or the substance which it is desired to detect in the gas samples, the gas sampling device may comprise further components For example, the gas sampling device may comprise a desiccator for drying gas samples in the first and second chambers Suitable desiccator substances are mentioned in US 4,987,816. The use of a desiccator may help to enhance the sensitivity of the indicator, particularly in applications where the device is used to test for the presence of ammonia in the gas samples. This is because it is believed that under certain conditions ammonia present in exhaled air may be removed from the air due to a process in which the ammonia is absorbed by water droplets present in the air, and may subsequently react with carbon dioxide dissolved in the water droplets thereby being converted into products, such as ammonium bicarbonate, which may not produce a response in certain indicators used to test for ammonia The use of a desiccator may reduce the amount of ammonia removed from the sample by this process, and may therefore improve the sensitivity of the response of certain indicators, particularly when there is a relatively long delay between collection of a sample and the response or inspection of the indicator.

Certain indicators may be relatively humidity sensitive, exhibiting different colour andlor intensity changes in the presence of different levels of humidity in the collected samples. In such cases a humidity sensor or sensors may be provided in contact with the first and second gas samples. The humidity sensor may then provide an indication of the levels of humidity present, thus allowing the state of the indicator to be cross referenced to an appropriate scale linking the appearance of the indicator to an amount of the substance to be detected under the appropriate humidity level. Other methods of correcting or taking into account the effect of humidity on the response of the indicator or indicators may be used, as known in the art. For example, changes in the humidity in the respective chambers may be measured by monitoring the intensity of light scattered from a substrate which comprises the indicator substance. The observed change in intensity may be compared to a predetermined scale to determine a humidity level or change, or a change or level may be directly measured using appropriate equipment from the observed intensity change. For example, a spectrophotometric device may be used to quantify any changes in the scattered light intensity at certain wavelengths, which may differ fiom those wavelengths at which changes in the state of the indicator occur in response to the presence of the substance to be detected One of the chambers may advantageously be used as a control, e.g. indicating the appearance of the indicator when a given amount of the substance is present at a known humidity level. In other arrangements, the humidity levels within the chambers may be controlled to be at a known level, e.g. by introducing water to the chambers, from an external source, or by releasing a quantity of water provided within the device, and initially sealed from the interior of the respective chambers, into the chamber or chambers. For example, a quantity of water may be located in a pouch which may be punctured or subjected to pressure to release the water into a chamber.

It will be appreciated that as the device of the present invention allows a difference in the amount of a substance to be detected to be derived from the appearance of the indicators associated with the respective chambers, it is not necessary to conduct correction for e.g humidity levels etc. unless it is desired to obtain accurate absolute quantitative values for the amount of the substance present in each chamber.

It is known that the first part of the breath sample exhaled by a person may comprise air which was present in the oral or nasal cavities of the user. Such "dead space" air generally comprises atmospheric air, and therefore does not constitute true "alveolar" air that is useful for diagnosis. In clinical applications, the first and second chambers may be configured such that an initial portion of a breath sample supplied to a chamber is not collected in the chamber. For example, this may be achieved by an appropriate arrangement of valves which result in a portion of the air supplied to a chamber being exhausted firom the device e.g. for a predetermined time before a sample is collected. It may also be desirable to include outlets in devices intended for use in non-clinical applications for other reasons.

Preferably the first and second chambers thus comprise respective outlets allowing gas supplied to the chamber to be exhausted from the device. The outlets S may be configured in any suitable manner to allow gas to flow from the interior of the respective chamber to the exterior of the device. For example, as described in relation to the inlets above, the device may be provided with a single outlet to its exterior, with each chamber having a separate outlet within the device connected to the shared outlet to the exterior of the device However, preferably each chamber comprises a separate outlet connecting the interior of the chamber to the exterior of the device.

Preferably each outlet is configured to exhaust the first part of a sample of gas supplied to the respective chamber from the device. In this way, the initial part of a sample may be discarded, and only the subsequent part retained within the 1 S chamber By discarding the initial portion of a breath sample, it is possible to ensure that the sample retained in the chamber contains a greater proportion of the useful alveolar air The outlets may comprise one way valves for this purpose, which may be configured e.g to allow gas to leave the chamber when the pressure within the chamber exceeds that at the exterior device by more than a given amount, or which close after a given time In preferred embodiments, the outlets comprise valves configured to maintain the pressure within the associated chambers at a given level or range above that at the exterior of the device.

The outlets, when present, may be located in a similar way to the inlets. For example, the outlets may be provided on a mounting plate.

Although the gas sampling device in all of its aspects and embodiments above has been described in relation to a dual chamber device, it will be appreciated that the device may comprise more than two chambers. For example, the use of more than two chambers may allow the presence of a given substance in a gas to be monitored over a longer period, to provide more reliable results, or the effect of administration of more than one different activator to be assessed. In other contexts, gas samples taken from more than two different areas, or persons may be more easily compared. If further chambers are provided, they may incorporate any or all of the preferred features discussed above in respect of the first and second chambers Although the first and second chambers are preferably of similar constructions, it will be appreciated that the first and second chambers need not be of the same construction. Thus the first and second chambers may incorporate any or all of the features discussed above in any combination.

It will be appreciated that the invention in these further aspects may incorporate any or all of the features described in relation to the other aspects of the S invention.

The present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a view from above of a breath sampling device in its deflated configuration in accordance with a first embodiment of the present invention; Figure 2 comprises graphs showing the response of certain indicators suitable for use in devices in accordance with the invention for detecting ammonia in gaseous samples; Figure 3A is a horizontal cross-sectional view of a gas sampling device in accordance with a second embodiment of the present invention in its deflated 1 S configuration; Figure 3B is a horizontal cross-sectional view of the device shown in Figure 2A in its inflated configuration; Figure 3C is an end view of the gas sampling device shown in Figures 3A and 3B from the end which incorporates the inlets, Figure 4A is a horizontal cross-sectional view of a gas sampling device in accordance with a third embodiment of the present invention in its deflated configuration; Figure 4B shows the gas sampling device of Figure 4A in its inflated configuration; Figure 4C is an end-on view of the inflated gas sampling device shown in Figure 3B taken from the end with the inlets; Figure SA is a horizontal cross- sectional view of a gas sampling device in accordance with a fourth embodiment of the present invention in its deflated configuration; Figure 5B is a view of the gas sampling device shown in Figure SA in its inflated configuration; Figure SC is an end-on view of the inflated gas sampling device shown in Figure SB from the side of the inlets.

A breath sampling device in accordance with a first embodiment of the present invention will now be described with reference to Figure I. The breath sampling device is in the form of a bag 1 having first 3 and second S chambers. The bag 1 is formed from two sheets of heat fusible polymeric film material which are joined to one another by a peripheral seal 7, which, together with a central seal 9 define first and second chambers 3 and 5. The bag is about 20cm x 30cm in dimensions. Each chamber is about l Ocm x l Ocm x 2cm in size when inflated, and thus has a volume of 200 cm3.

The peripheral seal 7 acts to prevent the flow of gas between the atmosphere and the interior of the respective chambers 3 and 5. The central seal 9 provides a barrier between the first and second chambers 3 and 5, preventing the communication of gas between the interiors of the two chambers Each of the chambers is provided with a respective inlet 15, 17, incorporating a one-way valve 19, 21. The one -way valves 19, 21 allow the passage of gas into the respective chambers when a flow rate exceeds a predetermined minimum amount, but prevents the flow of gas out of the chambers 3, 5 In this way, the valves 19, 21 act with the seals 7 and 9 to provide first and second chambers 3, S which are sealed from each other and the surrounding atmosphere of the bag 1 thus reducing the risk of contamination.

The device also includes first and second outlets, 26 and 27, associated with the first and second chambers respectively. These outlets include one way valves 28, 29, which allow air to flow out of the respective chambers to the exterior of the device when the pressure within the associated chamber exceeds that surrounding the device by a predetermined amount. In this way, the outlets 26 and 27 allow a portion of a breath sample introduced to the first or second chamber to be exhausted from the device, increasing the proportion of alveolar air in the samples retained in the first and second chambers 3 and S. The one way valves 28, 29 act to prevent the passage of gas out of the first and second chambers, and to prevent the entry of gas into the chambers from the atmosphere, once collection of the samples is complete.

The one-way seals 19, 21 also act to prevent the passage of gas from the atmosphere into the first and second chambers 3, 5, when the bag is in its initial deflated state, prior to use. In this way, premature activation of the indicator 25 is prevented.

The polymeric film material from which the gas sampling device 1 is formed is impenetrable to gases, and therefore provides a barrier preventing the passage of gas through the walls of the device from the interior of the first and second chambers 3, S and the surrounding atmosphere. The inlets 1 S. 17 and the valves 19, 21 are formed from plastics materials and are flat. In this way, the embodiment of Figure 1 provides a gas sampling device which is flat in its deflated configuration, and may be more easily stored.

A transparent window 23 extends across one of the surfaces of the bag, covering a part of the wall of each of the first and second chambers 3, S. and the seal 9 between the chambers. An indicator 25 is mounted on the interior surface of the bag 1, extending from the first chamber 3 across the seal 9 to the second chamber 5 in the region of the transparent window 23. The indicator is in the form of an indicating solution carried on a porous paper substrate.

The indicator 25 has a first section A associated with the first chamber 3, and which may come into contact with a gas collected in the chamber 3. The indicator has a second portion B in the region of the seal 9 separating the first 3 and second S chambers. The indicator has a third section C, which may contact a gas collected in the second chamber S. The portion B of the indicator is prevented from coming into contact with atmospheric gas or gases contained in either of the first and second chambers 3, 5, by the seal 9, and therefore may provide a reference part of the indicator, which will remain the original unchanged colour which the indicator exhibits in the absence of the substance to be detected after collection of gas samples in the first and second chambers. In this way, the parts of the indicator A and C associated with the first and second chambers 3 and 5 may be compared to this reference part B of the indicator to determine whether a colour change has occurred, and, if appropriate, the intensity of the colour change.

The nature of the indicator 25 will depend upon the substance which the bag 1 is intended to detect in samples of gas contained in the first 3 and second 5 chambers. It will be appreciated that the components of the bag 1 should be formed from materials which do not interfere with the ability of the indicator 25 to contact gas samples in the first 3 and second 5 chambers, and respond should a substance be detected present in either of these samples.

The bag 1 is intended for single use only. All of the components of the bag 1 are thus biodegradable or made from materials which are compatible with appropriate disposal practices for single use medical products. Thus the bag 1 should not comprise materials which present a hazard to the environment when incinerated or buried in accordance with usual disposal practices. In this way the bag I provides a gas sampling device which may be readily disposed of without harm to the surrounding environment.

The indicator may, for example, be any reagent which exhibits a colour or intensity change on detection of a given substance. It will be appreciated that the gas sampling device of the present invention is particularly suitable for determining a difference in the amounts of a substance present in first and second samples of a gas. Advantageously, therefore, the indicator 25 exhibits a colour change which differs in intensity or shade in response to the detected amount of the substance.

Use of the breath sampling device of Figure I to detect ammonia in first and second breath samples will now be described. The indicator used is curcumin. The curcumin is immobilised on a filter paper which is adhered to the interior surface of the bag I in the region of the transparent window 23 to provide indicator 25.

Curcumin is a natural substance extracted from a plant, and therefore provides an inexpensive indicator which may be safely used in a gas sampling device intended for use in a clinical context, and which is biodegradable after use without detriment to the environment. Curcumin undergoes a visible colour change on exposure to gaseous ammonia from yellow to red brown.

Initially, the bag 1 is in a deflated state, with the first 3 and second 5 chambers evacuated. A patient provides a first breath sample which is collected by the first chamber 3 by breathing through a straw connected to the inlet 15 to inflate the first chamber. The one-way valve 19 opens to allow the breath to flow into the chamber 3. The one way valve 28 in outlet 26 opens to allow gas to flow out of the chamber when the pressure within the chamber exceeds a predetermined level, thus increasing the amount of alveolar air collected Once the chamber is inflated, the straw is withdrawn, and the one-way valves 19 and 28 close to seal the breath sample in the first chamber 3 One minute after the breath sample is provided, the colour of the indicator 25 in the part A associated with the first chamber 3is noted, and compared with the reference portion B to determine whether any colour change has occurred. The transparent window surrounding the indicator 25 enhances the visibility of the indicator, and makes a colour change more readily apparent This first result is known as the base line.

The patient is then given a drink containing dissolved urea powder or another substance which activates the activity of H. Pylori bacteria. After an interval sufficiently long to allow the activator to reach the patient's gastro intestinal system, and for any H. Pylori urease enzyme present in the gastro intestinal system to react to it, the patient provides a second breath sample via a straw through inlet 17 to the second chamber 5. The one way valve 29 in outlet 27 opens to allow gas to flow out of the second chamber 5 when pressure in the chamber exceeds that outside the chamber by a predetermined amount Typically a 15 minute interval is appropriate to allow the ingested activator sufficient contact with any H. Pylori present in the patient's gastro intestinal tract. It is not necessary to mark the urea tablet or activator using any substance, such as i3C, as required by some conventional tests, as the use of two chambers provides an inbuilt "control", allowing the production of ammonia by means other than the action of H. Pylori bacteria to be accounted for.

After the patient has inflated the second chamber, the straw is withdrawn from the inlet 17, and the one-way valve 21 acts to seal the second breath sample in the second chamber 5. One minute after the second breath sample has been provided, the colour of the indicator portion C associated with the second chamber 5 is noted. The colour of the indicator in the portions associated with the first and second chambers, A and C, is compared to determine whether a difference in the amounts of ammonia present in the two samples exists.

The first breath sample provided by the patient may have included ammonia present in the body for reasons unconnected to a H. Pylori infection For example, certain oral and dental conditions, or renal failure may result in ammonia production. The state of the indicator in part A indicates the level of ammonia "base line" level of ammonia present in the patient's body for all possible reasons It is known H. Pylori excretes an enzyme urease which catalyses the breakdown of urea into ammonia and carbon dioxide. This enzyme is not normally present in the human body, in the absence of H. Pylori infection. If H. Pylori bacteria are present in a patient, they will break down the urea ingested by the patient before the second sample is taken, resulting in the production of an additional quantity of ammonia, over and above the "base line" quantity detected in the first breath sample. If a comparison of the portion of the indicator C associated with the second chamber in which the second breath sample provided after administration of urea is collected, and the first portion A of the indicator associated with the first chamber 3 indicates that a greater quantity of ammonia was present in the second breath sample, this additional quantity of ammonia may be attributed to the presence of H. Pylori in the patient's gastro intestinal tract, indicating a likelihood of H. Pylori infection.

It will be understood that in this way, the first breath sample provides a control sample against which the post activator administration reading may be compared to determine whether H. Pylori infection is present. The use of two readings in this way may reduce the risk of false positive readings, which might otherwise arise, if only one sample was collected, due to the presence of ammonia in the breath as a result of conditions unrelated to H. Pylori infection.

The gas sampling device 1 provides a way in which the amounts of ammonia present in two breath samples may readily be compared by comparison of the colour of the indicator in portions A and C. It will be appreciated that even small differences in the quantity of ammonia present may be detected visually in this way S by the human eye, without the need for any additional or elechronic equipment. This is because the human eye is relatively sensitive to a difference in colour or intensity of a colour. If desired, the colours of the indicator after exposure to the first and second breath samples may be compared to a scale to determine a quantitative value for the amount of ammonia present in each of the samples. Alternatively or additionally, the indicator may be subjected to additional e.g. electronic processing to derive more accurate values for the amounts of ammonia present in the respective samples. However, the breath sampling device 1 provides a simple and effective way for a diagnosis to be made in conditions where access to more complex equipmentis not readily available, by simple visual observation by the unaided human eye from the exterior of the bag. in some situations, the gas sampling device 1 may be used to provide an initial diagnosis, to identify cases requiring further investigation by more sophisticated means It has been found that when curcumin indicator is used to detect the presence of ammonia in a breath sample, the threshold for detection of a change by the human eye in the quantity of ammonia present between the first and second samples may be around 1 to 2 ppm (parts per million) Levels of ammonia lower than 1 ppm may be detected using appropriate e.g electronic processing equipment As discussed above, the present invention has general applicability to the detection of substances is gaseous samples, not necessarily in the clinical context For example, using an appropriate indicator such as curcumin, the device 1 may be used to detect ammonia in a confined space where potentially hazardous concentrations can build-up, such as a livestock shed, or food production area. A first gas sample from an area to be tested may be introduced into the first chamber 3 through the inlet 1 S by means of e.g. a syringe. This sample may be used as a control, for example giving a base line reading for the amount of ammonia present in an atmosphere before a potentially ammonia producing activity takes place, such as food production, or the inhroduction of livestock. A second gas sample may then be taken at a later stage when it is thought that ammonia may have built-up by introducing a gas sample from the same area by means of a syringe through inlet 17 into the second chamber 5. The state of the indicator in portions A and C may then be compared to determine whether a change in the amount of ammonia present in the atmosphere has occurred.

Alternatively, the two samples may be samples taken from different regions of the same confined space, e.g. to determine whether a difference in the concentration of ammonia exists with respect to different parts of the area, or, the first chamber 1 may, for example be filled with a sample of gas containing a threshold "safe" unmount of a substance, such as ammonia, against which a second sample contained in the second chamber may be compared, to determine whether the amount of the substance exceeds the threshold value in the second sample.

Depending upon the indicator used, and the intensity of the colour change produced on detection of a given substance in either of the first and second chambers, or the wavelength of the initial and final colours of the indicator, the indicator 25 may be viewed through a filter, or under illumination by a source emitting light of a particular wavelength which enhances the visibility of any change l S in colour or intensity. A filter may be incorporated in the bag 1, overlying the indicator 25 in the region of the window 23. For example, when the indicator is curcumin, a filter transmitting light at around 550 nm may enhance visibility of the colour change which occurs around approximately this wavelength.

After use, the bag I may be sealed in an additional container, to provide a controlled environment, preserving the results indicated by indicator 25 over time, if the device is to be stored for further reference or analysis, or transported.

The gas sampling device of the present invention may also provide a way of eliminating interference arising due to certain atmospheric conditions, or other constituents present in the gas samples provided to the chambers. For example, the humidity of a sample may in some cases affect the response of an indicator, or the sample may include other substances, other than that which the indicator is intended to detect, to which the indicator may respond. As any of these potentially interfering substances are likely to be present in both of the first and second samples, such substances are unlikely to affect a relative difference for the amount of the substance to be detected determined between the two samples.

Depending upon the nature of the substance to be detected in the first and second gas samples, and the nature of the indicator, further substances may be incorporated in the bag 1. For example, desiccating substances may be provided to dry gas samples provided to the chambers, if the presence of moisture is likely to affect results indicated by the indicator used.

It will be appreciated that rather than providing a single indicator strip extending between the first and second chambers 3, 5 as in Figure 1, discrete indicators may be provided associated with each of the chambers, or the whole of the material forming the first and second chambers may be joined to or impregnated S with, an indicating substance. The indicators associated with each chamber may be different substances provided that they are responsive to the same substance to be detected.

One possible method which may be used to manufacture an indicator for use in detecting ammonia will now be described with reference to Figure 2. Turmeric or curcumin is dissolved in ethanol to form a saturated solution. If turmeric is used it is necessary to wait for at least an hour to ensure that a suff cient amount of curcumin has been extracted to form a saturated solution and that all sediments have settled.

A suitable porous support material such as a pure filter paper is then dipped into the saturated solution and left in air for approximately 30 minutes to ensure that all ethanol has evaporated. The treated filter paper is then cut up into appropriately sized pieces for sensing gaseous ammonia These pieces may then be attached to the gas sampling device as shown in Figure 1. An indicator can also be provided in other ways, for example by applying a suitable quantity of a solution containing curcumin to the material from which the gas sampling device is made. The material may, for example, be dipped in a curcumin solution before manufacture of the device, or the indicating solution may be applied to the device after manufacture It is known that ambient humidity variations affect the intensity of the colour change of curcumin indicators. Fig. 2(a) shows in detail the responses of a curcumin indicator to gaseous air samples containing S parts per million (ppm), 10 ppm and 50 ppm of ammonia in the absence of any humidity. Fig. 2(b) shows the response of another indicator (of the same type) to ammonia at 50% relative humidity. Fig 2(c) shows the response of yet another indicator (also of the same type) to ammonia at 50% relative humidity, but this indicator was moistened with distilled water immediately prior to exposure to mitigate the effects of the ambient humidity For the traces shown in Figs. 2(b) and 2(c) the gaseous air samples contained the following concentrations of ammonia: I ppm, S ppm, 10 ppm, 20 ppm and 50 ppm.

In each case, the greater the concentration of ammonia in the sample, the larger the peak signal recorded.

In order to record the data shown in 1; igs. 2(a-c), indicators were placed in a glass chamber with inlet and outlet ports. The inlet port was connected to a mixing chamber of a gas rig that was previously calibrated Different concentrations of ammonia were obtained by varying the relative flow rates of gases into the mixing chamber. Although the indicators exhibited rapid colour change upon exposure to ammonia they were exposed to test atmospheres for two minutes to ensure that equilibrium was reached. Indicators showed a slow recovery after the ammonia containing atmosphere was removed and fully recovered after a period of 15 minutes. However, fresh indicators were used for each test. The reflected light spectrum of each sensor was recorded before and immediately after exposure to ammonia with a fibre optic reflective probe using a white light source and a miniature spectrometer. The intensities of colour changes were calculated as a percentage of the initial signal and are plotted in Figure 2(a) -(c).

It can be seen that the response of the indicator is humidity-dependent, and that the sensitivity is greatest at a wavelength around 550 nm. However, even in dry air the sensor is able to give reliable quantitative results. When measurements are taken using suitable analytical apparatus (e.g. a spectrophotometer), as will generally be the case for quantitative sensing, the best results can be obtained when the applied wavelength of light used closely matches the peak of the analyte-induced spectral changes of curcumin, i.e. around 550 nm. This can be achieved by controlling the spectral bandwidth of either the illumination source or the detector.

If it is desired to obtain an accurate absolute quantitative value for the amounts of a substance present in the chambers, the relative humidity of the gaseous samples under examination may be measured separately in known manner, in order to correct the readings appropriately. For example, a humidity sensor or sensors may be incorporated in the device, or the device may be subjected to further analysis to determine a humidity level. The effect of relative humidity on the response obtained has been found to be dependent on a number of factors, including particularly the nature of the substrate on which the curcumin indicator is immobilised These considerations must be factored into any correction. In some contexts, the level of humidity within the first and second chambers may be controlled to be at a predetermined level. For example, moisture may be introduced to the chambers from an external source, or e.g. by releasing a quantity of water from a sealed compartment within the device so that it enters a chamber. When the device is used to detect the presence of a substance in breath samples, the effects of relative humidity may not be a significant issue in practice, as human breath can be assumed to be close to 100% relative humidity.

Some further embodiments of the present invention will now be described with reference to Figures 3A to C, 4A and C and 5A to C. Operation of the gas sampling devices disclosed in these further embodiments is identical to that of the embodiment shown in Figure 1. These further embodiments may include any or all of the features described in relation to the embodiment shown in Figure I. In particular when the devices to be used to collect breath samples, outlets are preferably provided to increase the proportion of alveolar air collected as described in relation to Fig. 1.

The gas sampling device 30 shown in Figures 3A to 3C comprises first 32 and second chambers 34. These chambers are in the form of two corrugated plastic containers, which are independently extensible from a deflated configuration shown in Figure 3A in a concertina-like manner to an expanded configuration as shown in Figure 3B. Each of the chambers comprises a separate base plate 38,40.

The first 32 and second 34 chambers are attached to a mounting plate 36 at one end The mounting plate 36 closes one end of each container with the exception of two inlets 42,44. The first and second chambers 32,34 may be separately inflated by supplying air through the respective inlet 42,44 to the interior of the chamber. The inlets 42,44 may incorporate any suitable valve arrangement as described above in relation to Figure l to prevent the escape of gas provided to the chambers after inflation.

Figure 3C, which is an end view of the mounting plate 36, shows certain further features of the gas sampling device 30 in more detail It will be seen that the mounting plate 36 further incorporates a transparent window 46, to which an indicator 48 is adhered. The indicator has a first part A' which may contact a gas sample contained in the first chamber 32, a second portion B' which is located in the part of the base plate 36 between the first chamber 34 and the second chamber 34, and which is therefore not in contact with the gas samples contained in either of those chambers, and a part C', which may contact a gas sample contained in the second chamber 34.

Once the first chamber 32 has been inflated, and a result obtained for an amount of a substance to be detected determined from the state of indicator portion A', the first chamber 32 may be deflated, and the part of the base plate 36 containing indicator portion A' severed from the remainder of the device 30, and sent for further analysis, e.g. by electronic means The second chamber 34 may be then inflated, and once indicator portion C' has exhibited any change, deflated, and the portion of the base plate containing indicator part C' subjected to further analysis.

Alternatively, the base plate 36 containing the entire indicator 48 may be separated from the first and second chambers 32,34 after deflation of the respective chambers.

In this way, the device as shown in the embodiments of Figures 2A to 2C provides a portion which may be detached from the chambers 32, 34 after use, and stored, or sent for further analysis, without the need to retain the whole device.

Figures 4A to 4C show a further embodiment of a gas sampling device in S accordance with the present invention. The gas sampling device 50 includes a first chamber 52 and a second chamber 54 attached to a mounting plate 56. Inlets 58 and associated with the respective chambers 52, 54 are provided on a mounting plate 56.

In their deflated state shown in Figure 4A, the first and second chambers 52, 54 are in a coiled configuration. On inflation, each of the chambers 52, 54 extends to the position shown in Figure 4B. When both ofthe chambers are inflated, they are substantially parallel to one another.

Figure 4C is an end view of the mounting plate 56 when the first and second chambers 52, 54 are in their extended state shown in Figure 4B. The mounting plate 56 has a transparent window 62 on which indicator 64 is provided. The indicator has a first portion labelled A" which may contact a gas sample present in the first chamber 52, and a second portion B" which may contact a gas sample contained in the first chamber 54. A further part of the indicator C" extends between the parts and A" and B" to provide a reference area The mounting plate 56 may be severed from the first and second chambers after they have been deflated as described in relation to the embodiment shown in Figure 3A to 3C.

A further embodiment of the gas sampling device of the present invention is shown in Figures 5A to 5C The gas sampling device 60 includes first chamber 62 and a second chamber 64. The chambers are mounted to a mounting plate 66. The mounting plate 68 is transparent. Mounting plate 66 is provided with inlets 70, 72 associated with the first and second chambers. Each chamber has an end plate 74, 76 A support 68 extends across the width of the other ends of the chambers 62, 64, and, with end wall 69, forms a gas tight seal separating the interiors of the first and second chambers 62, 64.

In this embodiment, on inflation, each of the chambers expands in a concertina-like manner from the deflated configuration shown in Figure 5A to the inflated configuration of Figure 5B. The chambers therefore expand perpendicular to the fluid inlets, and in opposite directions to one another. The separating wall 68 provides a fluid tight barrier separating the first and second chambers 62, 64.

As the end on view of Figure SC shows, the mounting plate 68 is provided with an indicator 78 having portions which may contact gas samples contained in the first and second chambers respectively as described in the earlier embodiments, and a portion between these which overlies separating wall 68, and may therefore act as a reference. The parts of the indicator 78 associated with the first and second chambers respectively are labelled A"' and C"' and the reference section B"'. As in the embodiments shown in Figures 3A to C and 4A to C, the mounting plate 68 may be separated from the chambers 62, 64 to provide a record of the results obtained, for storage or subjection to further analysis Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims. - 39

Claims (1)

1. Claims.

   1 A gas sampling device, the device comprising a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas; the first and second chambers each comprising an indicator for providing a detectable indication when a substance to be detected is present in a gas sample collected in the r espective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance whereby a difference in the amounts of a substance present in gas samples collected in the first and second chambers may be detected 2 The gas sampling device claim wherein the first chamber is separated from the second chamber by a gas impervious barrier.

   3 The gas sampling device wherein the first and second chambers are

   inflatable

   4. The gas sampling device of any of claims I to 3 wherein the first and second chambers are separate containers which are not attached to one another along their length, the chambers being attached to a common mounting plate 5. The gas sampling device of claim 4 wherein the chambers extend as they inflate from a coiled deflated configuration 6 The gas sampling device of claim 4 wherein the chambers extend in a concertina-like manner from a deflated configuration 7 The gas sampling device of any of claims I to 3 wherein the gas sampling device comprises first and second sheets of heat fusible plastics material selectively thermally bonded to one another to provide first and second chambers.

   8 The gas sampling device of any preceding claim wherein the first and second chambers are arranged in side-by-side configuration. -

   9 The gas sampling device of any of claims 1 to 7 wherein the first and second chambers are arranged in end-to-end configuration.

   The gas sampling device of any preceding claim wherein separate inlets are S provided between the exterior of the gas sampling device and the interior of the first and second chambers.

   1 1. The gas sampling device of claim 10 wherein the first and second inlets comprise one-way valves which inhibit the passage of gas out of the first and second 1 0 chambers.

   12. The gas sampling device according to any preceding claim wherein the indicators associated with the first and second chambers are provided on a portion of the device which is severable from the first and second chambers 13 The gas sampling device of any preceding claim wherein the first and second chambers comprise respective outlets allowing gas supplied to the chamber to be exhausted from the device.

   14 The gas sampling device of claim 13 wherein each outlet is configured to exhaust the first part of a sample of gas supplied to the respective chamber from the device 1 S The gas sampling device of any preceding claim wherein a single indicator is provided which extends between the first and second chambers having first and second portions associated with the first and second chambers 16. The gas sampling device according to any preceding claim wherein the gas sampling device includes a reference sample of the indicator or indicators associated with the first and second chambers which is prevented from coming into contact with gas samples collected in the first and second chambers.

   17. The gas sampling device according to any preceding claim wherein the first and second chambers of the gas sampling device are formed from a material which comprises an indicator. - 41

   18. The gas sampling device of any preceding claim wherein the same indicator substance is associated with the first and second chambers 19. The gas sampling device of any preceding claim wherein the detectable S indication is a visible indication A gas sampling device, the device comprising: a first chamber having an inlet for collecting a first sample of gas; and a second chamber having an inlet for collecting a second sample of gas; l O the first and second chambers each comprising an indicator for providing a visible indication when a substance to be detected is present in a gas sample collected in the respective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance whereby a difference in the amounts of a substance present in gas samples to be collected in the first and second chambers may be detected 21 The gas sampling device of any preceding claim wherein primary indicators are provided associated with each chamber for providing a visible indication when a substance to be detected is present in a sample of gas collected in the chamber, and secondary indicators are provided associated with each of the chambers for providing a non-visible indication when a substance to be detected is present in the respective chambers.

   22 The gas sampling device of any preceding claim wherein the indicator exhibits a detectable change in response to an increase in the amount of the substance to be detected being present in a gaseous sample.

   23 The gas sampling device of any preceding claim wherein the indicator exhibits an increase in intensity of a colour change in response to an increase in the amount of the substance to be detected being present in a sample 24 The gas sampling device of any preceding claim wherein the indicators associated with the first and second chambers of the device exhibit a detectable change in response to the presence of ammonia in a gas sample collected in the chamber - 42 A gas sampling device for the detection of ammonia in first and second gas samples, which device comprises a first chamber having an inlet for collecting a first sample; a second chamber having an inlet for collecting a second gas sample; the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a gas sample collected in the chamber, whereby a difference in the amounts of ammonia present in gas samples collected in the first and second chambers may be detected.

   26. A gas sampling device for the detection of ammonia in samples of breath exhaled by a person, which device comprises a first chamber having an inlet for collecting a first breath sample; and a second chamber having an inlet for collecting a second breath sample, the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a breath sample collected in the chamber, thereby allowing a difference in an amount of ammonia present in breath samples collected in the first and second chambers to be detected 27 The gas sampling device according to any preceding claim wherein the indicator comprises curcumin 28 A method of detecting a difference in the amount of a substance present in first and second gas samples using a gas sampling device in accordance with any preceding claim, the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in the second chamber, and comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second samples of gas to determine a difference in the amounts of a substance to be detected present in the first and second gas samples.

   29. A method for detecting a difference in the amounts of a substance present in first and second gas samples using a gas sampling device comprising: a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas, the first and second chambers each comprising an indicator for providing a detectable indication when a substance to be detected is present in a gas sample collected in the respective - 43 chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance; the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in the second chamber, and comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second samples of gas to determine a difference in the amounts of a substance to be detected present in the first and second gas samples.

   30. The method of claim 28 or claim 29 wherein the step of comparing the states of the indicators associated with the first and second chambers comprises visually comparing the states of the indicators.

   31. A method for detecting a difference in the amounts of a substance present in first and second gas samples using a gas sampling device comprising: a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas, the first and second chambers each comprising an indicator for providing a visible indication when a substance to be detected is present in a gas sample collected in the respective chamber, the indicators associated with the first and second chambers being responsive to the presence of the same substance to be detected; the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in the second chamber, and visually comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second samples of gas to determine a difference in the amounts of a substance to be detected present in the first and second samples 32. The method of any of claims 28 to 31 wherein said indicator provides a detectable indication when ammonia is present in a gas sample collected in the respective chamber, and the method comprises the step of comparing the states of the indicators associated with the respective first and second chambers on collection of the first and second samples of gas to determine a difference in the amounts of ammonia present in the first and second gas samples - 44 33 A method for detecting a difference in the amounts of ammonia present in first and second gas samples using a gas sampling device comprising a first chamber having an inlet for collecting a first sample of gas, and a second chamber having an inlet for collecting a second sample of gas, the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a gas sample collected in the respective chamber, the method comprising the steps of collecting a first sample of gas in the first chamber, collecting a second sample of gas in a second chamber, and comparing the states of the indicators associated with the respective first and second chambers are collection of the first and second samples of gas to determine a difference in the amounts of ammonia present in the first and second gas samples.

   34. The method of any of claims 28 to 33 wherein the gas samples are breath samples.

   35. A method for detecting a difference in the amounts of ammonia present in first and second breath samples using a breath sampling device comprising a first chamber having an inlet for collecting a first breath sample, and a second chamber having an inlet for collecting a second breath sample, the first and second chambers each comprising an indicator for providing a detectable indication when ammonia is present in a breath sample collected in the respective chamber, the method comprising the steps of collecting a first breath sample in the first chamber, collecting a second breath sample in the second chamber, and comparing the states of the indicators associated with the respective first and second chambers after collection of the first and second breath samples to determine a difference in the amounts of ammonia present in the first and second breath samples.

   36. A method of diagnosing H. Pylori infection using an ammonia detection device in accordance with any of claims I to 27 37. The gas sampling device or method of any preceding claim wherein the device is disposable after a single use.

   38. The gas sampling device or method of any preceding claim wherein the device is biodegradable. - 45

   39. A gas sampling device substantially as herein described and with reference to any one of the accompanying drawings.

   40. A method of detecting a difference in the amount of a substance present in first and second gas samples substantially as herein described and with reference to any one of the accompanying drawings.