WO2007022895A2 - Measuring device for optical determination of toxic gas concentration by transmission - Google Patents

Measuring device for optical determination of toxic gas concentration by transmission Download PDF

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Publication number
WO2007022895A2
WO2007022895A2 PCT/EP2006/008016 EP2006008016W WO2007022895A2 WO 2007022895 A2 WO2007022895 A2 WO 2007022895A2 EP 2006008016 W EP2006008016 W EP 2006008016W WO 2007022895 A2 WO2007022895 A2 WO 2007022895A2
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WO
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Patent type
Prior art keywords
means
measuring device
detection means
light
transmission
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PCT/EP2006/008016
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German (de)
French (fr)
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WO2007022895A3 (en )
Inventor
Michael Hanko
Jürgen HEINZE
Sara Rentmeister
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Albert-Ludwigs-Universität Freiburg
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/75Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/78Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
    • G01N21/783Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour for analysing gases
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00Sampling; Preparing specimens for investigation
    • G01N1/02Devices for withdrawing samples
    • G01N1/22Devices for withdrawing samples in the gaseous state
    • G01N1/24Suction devices
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/01Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03Cuvette constructions
    • G01N21/031Multipass arrangements
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N31/00Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
    • G01N31/22Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators

Abstract

The aim of the invention is to produce a measuring device by means of which the concentration of a toxic gas can be rapidly and simply determined. According to the invention, said aim is achieved by means of a measuring device for optical determination of the concentration of at least one toxic gas by transmission, comprising a measuring cell which is not transparent to light, with a housing in which a tubular at least partly transparent detection means, at least partly provided on the inner wall thereof with a transparent coating of a given layer thickness made from at least one polymeric material with at least one indicator substance immobilised therein, further comprising a pump or suction device arranged before or after the detection means, which pumps a toxic gas stream through the detection means and at least one light source and at least one receiver means arranged to one and/or more sides of the detection means, by means of which an absorption change for the indicator substance is measured by transmission as a function of time. The receiver means may be connected to an analysis unit.

Description

Measuring apparatus for optically determining a concentration of noxious gas in transmission

description

The present invention relates to a measuring device for optically determining the concentration of at least one harmful gas in transmission, as well as a corresponding method. Under noxious gas according to the present invention, a gaseous and / or vaporous component of a gas mixture is referred to.

The detection of harmful gases is particularly in environmental terms, but also in terms of job security is very important. known from the prior art, the so-called test tube, for example, the Dräger, Luebeck, which are filled with an impregnated with an indicator substance silica gel. Flows through a noxious gas, for which the absorbed in the silica gel indicator substance is sensitive, the test tube, so a gradually colored zone, whose intensity and time course is in communication with the concentration of the gas to be detected is formed due to the reaction with the indicator substance. These color zone is visually evaluated according to their progress in the test tube, and the gas concentration is read off from a scale printed on the tube.

A disadvantage of this prior art that due to the visual evaluation of the test tubes a large Ableseungenauigkeit is given especially in the presence of diffuse color zone boundaries. Another big disadvantage is that the known test tubes have a relatively low sensitivity, and the measurement time should be relatively long, as must be done for a visually perceptible color change, a high molar conversion.

Object of the present invention is therefore to provide a measuring apparatus, with which the concentration of harmful gases quickly and accurately in a simple

As can be determined.

This object is achieved by a measuring device for optically determining the concentration of at least one harmful gas in transmission, comprising a lichtun- permeable measuring cell having a housing in which a tube-shaped, at least partially transparent, preferably optically transparent detecting means that a on its inner wall at least partially comprises light-transmissive, preferably optically transparent feed with a predeterminable layer thickness of at least one po- lymeren material with an immobilized in this indicator substance is arranged, further comprising the detection means upstream or downstream of pumping or suction device which conducts a noxious gas stream through the detection means and at least one light source and at least one receiver means, which are arranged on one and / or more sides of the detection means by means of which in transmission, an absorption change of the indica torsubstanz is measured in function of time, wherein the receiver means to an evaluation unit is connectable. The measuring device according to the invention has the great advantage that, through the line of a constant volume flow by means of pumping or suction device via the detection means reproducible results obtained very fast, on the other hand by the measurement in transmission with high accuracy the noxious gas concentration can be determined. The carrier means of the detection means is preferably disposed at least partially translucent, further preferably made of a transparent and clear, and in particular gas-impermeable material, for example glass and / or suitable plastics. The inventive measuring device is not stationary sensitive with regard to the positioning of the detection means while, as just contrary to the prior art, no ink fountain history is measured.

The polymer, at least partially on the inner wall applied material to be applied to the detection layer is preferably selected from a group comprising polysiloxanes, polycarbonates, polyacrylates, polymethacrylates, Perfluorpo- lyether, polystyrenes, polyolefins, polyisocyanates, polyols, polyamines, polyamides, polyesters, polyvinyls, polyimines, polyglycols, polyphenylene oxides, polysulfones and / or Polyethersul- fone and derivatives thereof. The inventively employed materials can be preferably used as copolymers, block copolymers. Particularly preferred silicone-polycarbonate block copolymers are. The coating of the detection means can contain both pure polymers and polymer blends. Likewise as a synthesis of the polymeric material on the detection means from precursors with simultaneous or subsequent immobilization of the indicator reagent is possible. It can also be provided that the coating of the detection means consists of several layers, these layers may each comprise different indicator substances. However, it can also be provided that several different indicator substances are incorporated in a single layer. The indicator substance is preferably a particularly homogeneous recorded in the polymeric material color indicator, this is preferably soluble in the polymeric material, and is further preferably selected from a group comprising Dipheny- lamin, indigo, o-tolidine, phenylenediamine and / or bromophenol blue and their derivatives, where particularly preferred are diphenylamine, 4,4'-Dinonoxy-7,7'-Dimethoxyindigo, o- tolidine, N, N'-diphenyl-1, 4-phenylenediamine and / or bromophenol blue.

The indicator substance is immobilized in the polymeric material before. The immobilization can be effected in particular via hydrogen bonds. Therefore, as polymeric materials for the purposes of the present invention are those polymers are preferred which have chemical groups for forming hydrogen bonds. As such chemical groups are both CO-groups, which act in the formation of a hydrogen bond acceptors of hydrogen atoms as well as OH, NH, NH 2 - and which act as donors of hydrogen atoms SH-groups, in ques- tion. Preferably in the formed layer, the preferred polymeric material has a high permeability for the component to be detected of the gas mixture, that is, the / the pollutant gases (s) on. However, it is also possible that the immobilization of the indicator substance in the polymeric material made via the dipole-dipole interactions, Van der Waals interactions or even covalent bonds.

The detection means is prepared by coating a support means comprising a polymeric material and the at least one to be immobilized in this indicator substance. The application of the coating can be carried out by any known method, for example by brushing by means of pull knife coating or brushing, atomizing, dipping (dip coating), spraying or molding. Thereby making the detection means can be made inexpensively. Preferably, the coating of the Detekti- onsmittels a total thickness in a range from about 0.1 microns to about 1 mm, preferably the thickness is in a range from about 0.1 micron to about 50 microns, even more preferably in a range of about 1 micron to about 20 microns. The choice of the thickness of the layer of the polymeric material with the immobilized in the indicator substance depends, among other things, from the latter, in particular the quantity of the indicator substance, the polymeric material can be loaded. Preference is given to the quantity of the indicator substance% lies in the polymeric material in a range of about 0.1 wt. To about 120 wt.%, Based on the respectively used polymeric material. The amount of the rial recorded in the polymeric Mate indicator substance depends on one hand on the chemical compatibility of the polymeric material with the respective indicator substance, on the other hand also on the layer thickness of the polymeric material employed. By increasing the quantity of the indicator substance in the polymeric material, the sensitivity can be increased considerably. The indicator substance is preferably applied together with the polymer material on the support means of the detection means. By Aufbrin- supply a coating on the inner wall of the detection means is the flowing noxious gas only a very small volume element with the indicator substance offered to give a quick response is possible. The harmful gas flows preferably essentially by convection through the detection means. This makes the measurement of the noxious gas can be done very quickly.

The measuring device of the invention has a tube-shaped design detection means. The inner wall of the tube-shaped detection means is at least partially, ie, provided in the region of the measurement beam with the coating. The gas impermeable tube serves as a carrier for the coating. Preferably, the coating of the carrier with a polymeric material and at least one takes place in this case in this indicator substance immobilized by means of dip coating. Subsequently, which applied to the outer wall of the tube polymeric layer is then easily removed by a solvent such as acetone, or the tube, is protected during the dip-coating process by a removable medium, such as Scotch tape from the outside. there are preferably used as tubes or support means, those of glass, in particular those made of borosilicate glass. The design of the detection means in the form of a tube has the great advantage that on the one hand the tube before insertion into the measurement device gas-tight manner by means of, for example, films which are arranged on both ends of the detection tube can be closed off by methods according to the prior art. Contamination of the detection means before use in the inventive measuring device is safely avoided. The films are preferably formed such that they can be easily opened by piercing. Appropriate auxiliaries therefor are provided in the receiving of the measuring cell, which act here additionally aufgenom- mene in a groove sealing means against the ends of the tubular sealing detection means. In this way, a change in the volume flow caused by the pump through lateral outflow of gas is also prevented. Instead of a groove, however, any other recording can be provided which is adapted to allow a sealing means for sealing of the detection means within the measuring cell of the measuring device erfindungsgemä- SEN. The sealing means is preferably formed as a sealing ring which can also be formed profiled. In a further preferred embodiment of the measuring device according to the invention the at least one receiver means are designed as a photodiode, phototransistor and / or photoresistor. Preference is given to the receiver means is formed small construction. By this means it is possible to use in combination with a correspondingly small-sized light source, which is preferably designed as LEDs, even relatively small built detection means, in particular in the form of a tube, so that here over the entire light conduit between the light source and receiver means executive a constant volume flow of the gas can be made uniform and above all rapid determination of the noxious gas concentration by means of pumping or suction device. However, it is also possible to use any other light detectors, which are known from the prior art as a receiver means.

The measuring device according to the invention preferably has a pumping or suction device, which with a constant, preferably high flow rate in a range of preferably about 100 to 10,000 ml / min, more preferably about 1000 to 2000 ml / min sucks the noxious gas. The harmful gas is thereby guided smoothly across the sensitive layer of the detection means. Preferably is provided that the pumping and suction device is arranged below the detection means in the inventive measuring device, wherein the pumping and suction device can be arranged with sufficient miniaturization also within the measuring cell. In this way, the noxious gas stream is sucked evenly across the sensitive layer of the detection means. There can be provided a usual known from the prior art pumping or suction device, preferably a suction device.

More preferably, the measuring device of the invention to a humidity and / or temperature and / or mass flow sensor. This can be upstream or below the detection means, preferably below the detection means, but may be arranged before the pumping or suction device. By correlation with the measured humidity and / or temperature and / or the mass flow, the noxious gas concentration can be determined very accurately. The humidity and / or temperature and / or mass flow sensor is preferably connected to the same evaluation as the measuring cell, whereby the pump device can be connected to the evaluation unit additionally. The evaluation unit advantageously comprises an AD converter for digitizing the measurement signal, and advantageously a PC interface for control and evaluation of the measurement data by means of a software or a micro-controller for stand-alone operation on site.

In a preferred embodiment of the present invention, a wall of the receiving of the measuring cell is at least partially provided with a reflective surface. This makes it possible to achieve an increased sensitivity of the measuring device of the invention, as being guided by the reflection inside the receiving the light beam more than once through the coating of the detection means. Thereby the light source and the receiver means on one side, but optionally beispielswei- se also be arranged on opposite sides of the detection means. An increase in the sensitivity of the measuring device of the invention can also be achieved, for example, that several light sources and receiver means are provided. This also light sources with different wavelengths can be used under certain circumstances. determining the noxious gas concentration in the UWVIS- and / or NIR range is preferably done so that corresponding light sources may be used. The wavelength of the respective light sources is matched to the used indicator substance. Therefore, in order to achieve maximum flexibility of the measuring device according to the invention, therefore, are either a plurality of light sources of a specific wavelength selected with regard to the used indicator substance or to be determined noxious gas concentration, but it can also be selected, a light source which operates over a wide wavelength range.

The present invention further relates to a detection tube and a method for the optical determination of at least one harmful gas in transmission, where a noxious gas stream is passed through a valve disposed in a measurement cell detecting means, in the form of a tube with a constant volume flow, which has a coating of at least a polymeric material having, in which at least one indicator substance is immobilized, wherein at least one light beam is guided by the detecting means, and wherein the speed of the measurable transmission or voltage change from which a change in absorbance of the indicator substance can be determined at least in a partial region, and / or rate of absorbance change extends approximately linearly with the measured noxious gas concentration. This makes it advantageously possible to carry out very accurate measurement of harmful gas concentrations. In particular, the calibration of the inventive measuring device is greatly simplified, and thus determined at different gas concentrations and temperatures, and moisture content and / or mass flows measurement data by means of software may be implemented in the evaluation unit, so that here the determination of unknown harmful gas concentrations is easily possible. Harmful gases which chen means of the inventive measuring device and Detektionsröhr- and are preferably determined with the inventive method, nitrogen oxides are, in particular, nitrogen dioxide, sulfur dioxide, ozone, chlorine, ammonia and / or hydrogen sulfide.

the light beam is preferably according to the inventive method at least two times through the detection means. If the detection means tube-shaped Removing formed with a coating applied to the inner wall coating of a poly- meric material having at least one, in this immobilized indicator substance, the light beam by the transmission measurement is at least passed twice through the coating, in addition to the existing through the buckle coating caused magnification of the irradiated sensitive surface additionally contributes to an increase of the sensitivity of the inventive method. Is additionally still performed more times by an at least partially applied to a wall of the receiving reflective layer of the light beam through the particular tube-shaped detection means, a considerable increase in the sensitivity of the method according to the invention is achieved.

These and other advantages of the present invention will be explained in more detail using the following figures. Show it:

Fig. 1 is a perspective view of a detection agent of the invention for an inventive measuring device;

Fig. 2 is a schematic representation of the detection means, together with the coatable at the ends of the gas-tight foil;

Fig. 3 is a schematic representation of the measuring device of the invention;

FIG. 4 shows a sectional view through a measuring cell of the measuring device of the invention in a leading by the light source and the receiver means plane;

FIG. 5 shows a cross section through the measuring cell shown in Fig 4 in a through.

Light source and the receiver means leading level; FIG. 6 shows a second embodiment of a measuring cell; Fig. 7 shows a third embodiment of a measuring cell with a reflective

Wall of the receiving of the detection means;

8 shows a fourth embodiment of the measuring cell using a light guide or the formation of a light entry shaft;. Fig. 9 is a plot of the measured voltage change with the inventive measurement cell to the measurement time in the determination of nitrogen dioxide at a concentration of 2 ppm in Example 1;

Fig. 10 is a plot of FIG 9 at a concentration of nitrogen dioxide.

25 ppb according to Example 1; and FIG. 11 is a plot of the nitrogen concentration determined against

Rate of voltage change according to Example. 1

First, it should be noted that the disclosed in the figures features are not limited to those shown there each specific embodiments. Rather, the features respectively specified in the description, including the description of the figures and the drawings each for training are combined. Incidentally, the same features with the same reference numerals are referred to in the present figures.

Fig. 1 shows a perspective view of an overall denoted by the reference numeral 16 detection means, comprising a tube-like design support means 17 with a load applied to the inner wall 28 coating 18. Inside the detection means 16, a flow channel 40 is provided. Through this flow channel 40, the harmful gas is passed.

Fig. 2 shows for clarity here 16 wherein gas-impermeable films are arranged on the ends 32.1 and 32.2 30.1 and 30.2 of the detection tube the construction of the detection tube 16 in detail. Such reasonably trained Detektionsröhr- chen 16 can be stored for long periods of time and at the same time be sure to avoid any contamination by harmful gases from the atmosphere. It may be filled with a shade gas. The slides 32.1 and 32.2 are preferably formed pierceable.

Fig. 3 shows schematically the structure of an inventive measuring device 10. This comprises a measuring cell 12, a humidity and temperature sensor 34 as well as a pumping device 20, where the above elements are connected with an evaluation unit 26. The connection between the humidity and temperature sensor 34 is via terminals 52, that of the pumping device 20 via terminals 54. The humidity and temperature sensor 34 is 12, and the pump device 20 between the measuring cell, said pumping device 20 below the measuring cell 12 with respect gas stream is arranged on the marked by arrows 50 (pollutants).

The measuring cell 12 comprises a housing 14 in which a tube-shaped design detection means is accommodated sixteenth It is arranged on a longitudinal side of the detection means 16 a light source 22, and the opposite on the other longitudinal side of the detection means 16, a light receiver 24. Between these is a light channel 46, represented by an arrow, arranged. The light source 22 is via terminals 42, the receiver means 24, which is preferably formed as a photodiode, connected via terminals 44 to the evaluation unit 26th The light source 22 is preferably further formed as an LED. Obtained by the detection means 16, which is received in the measuring cell 12, flowing pollutant gas 50 reacts by flowing with a preferably constant and high volume flow generated by the pump device 20, which is arranged on said inner wall 28 of the tube-shaped carrier by means of the de- tektionsröhrchens 16 coating 18 in which a sensitive for the harmful gas indicator substance is immobilized. By transmission measurements in the light channel 46, a voltage change is first determined which integrated in the Auswerteein- umberechnet in a change in transmission 26 and a change in absorption as a function of time can be determined. By means of an evaluation unit 26 implemented in the software an unknown noxious gas concentration can then be determined. Calibration is possible directly via the voltage change.

Fig. 4 shows a longitudinal section through the measurement cell 12 of FIG. 3 in a plane which passes through the light source 22 and the receiver means 24. The measuring cell 12 is formed in two parts, preferably with a fixed part and a movable part 13.1 13.2. The movable part 13.2 can be placed in the direction of arrows 38 on the stationary part 13.1. The movable part 13.2 is releasably connected to the festste- Henden member 13.1, so that the use of a detection means 16 formed of a tubular carrier 17 is provided with a disposed on the inner wall coating 18 allows, said at both ends with a gastight film may be sealed. In the area of ​​a harmful gas inlet 64 and a harmful gas outlet 66 12, the part 13.1 or 13.2 of the measurement cell, a groove 58.1 or 58.2 on which is formed circumferentially. In these grooves 58.1 and 58.2 sealants are added 56.1 and 56.2, which are preferably designed as O-rings having a flattened cross-section. Between these grooves 58.1 and 58.2 and the harmful gas inlet 64 or the noxious gas outlet 66 of the measuring cell 12 is in the fixed part 13.1 a projecting mandrel 60 and formed, a mandrel 62 corresponding to the movable part 30.2 of the measuring cell 12th The mandrels 60 and 62 are preferably formed annularly without interruption. Now, if the detection means used in the direction of arrows 38 16 in the fixed part 13.1 is open, measuring cell 12, facing the fixed part 13.1 end arranged gastight film of the detection means is penetrated 16 by the ring-shaped mandrel 60, in which case the detection means 16 due the disposed in the groove 58.1 56.1 sealant is prevented from contamination with the atmo- sphere within the measuring cell. Subsequently, the movable part 13.2 of the measuring cell is placed 12 in the direction of arrows 38, wherein the at the end facing the detection means 16 arranged foil is pierced by the end annular dome 62nd Here, a protective gas can always be passed through the device 10 degrees. Preferably, when putting the movable part 13.2 a of electrical contact is closed to start the measurement process. Piercing both encryption circuit films when placing the part 13.2 in about the same time is also possible. In this way a continuous flow channel 40 is formed, in which a passed through the detection means 16 noxious gas concentration can be determined by means of the light channel 46 in transmission. The leads to the measuring cell 12 can thereby be pre forth freed of contaminating pollution gases, wherein the supply lines which are not shown in detail here, are in particular provided with check valves, so that from the resulting line pieces simply via a terminal, which also has a valve can be removed, possible harmful gases and replaced by a neutral atmosphere or an inert gas. the gas to be measured can then be in a constant volume flow, generated by means of the pump device 20 are passed through the detection means sixteenth

Fig. 5 shows the measurement cell 12 shown in FIG. 4 in a cross-section through the plane of the light source and the receiver means 24, whereby the principle of determination of a harmful gas concentration in transmission and the guiding of the light channel 46 is illustrated nochmalig.

Fig. 6 now shows an alternative measurement cell 12 which has in contrast to that shown in Fig. 4 a total of three light sources 22 and, correspondingly, three in particular formed as a photodiode receiver means 24. Thereby, the sensitivity of the measuring device 10 may on one hand be considerably increased, but it is also enables light, that with the provision of multiple indicator substances which are sensitive to different noxious gases, here on this tuned different light sources 22 are used, that is, having different wavelengths. Accordingly, the receiver means 24 are then formed here.

Fig. 7 now shows a third embodiment of a measuring cell 12, the inner wall 36 of the tube-shaped receptacle 14 is formed with a reflecting surface here. The light source 22 and the receiver means 24 are disposed on one side of the detection means 16 in the fixed part 13.1 of the measuring cell 12th The arrangement takes place each other slightly angled. With an arrow 48 while the path of an emitted from the light source 22 light beam is represented, which is seven times reflected at the reflecting inner wall 36 of the tubular receptacle 14 in total in the example given before it strikes the receiver means 24th Also accumulate a considerable increase in sensitivity of the measuring device 10 is possible.

Fig. 8 shows a fourth Ausfϋhrungsform a measuring cell 12 wherein at its end face the light source 22 is arranged here in the fixed part 13.1, whereas on the opposite side with respect to the detection means 16, a total of four receiving means 24 are disposed. In this region of the opposite festste- Henden part 13.1 of the measurement cell 12 in one embodiment, a light guide 68 is arranged, which allows over the entire cross-sectional area of ​​a light channel sixteenth In this way, the cross-section of light emitted from the light source 22 light channel is greatly expanded. In an alternative, the light source 22 is formed a light input shaft 68 below which a reflective layer up comprises a wall 70 so that, as exemplarily shown on the two light beams 48, where it is reflected to this wall 70, the light and the receiver means is passed 24th Also This results in a fanning out of the width of light emitted from the light source 22 light beam, so that by means of a plurality of receiver means 24 can be detected a voltage or change in transmission.

The light source 22 may be formed such principle that has these additional focus sierende means whereby a further increase in the sensitivity of the measuring device is achieved 10th Example 1 :

For cleaning the glass tube of borosilicate glass of the Sl MAX ® brand, company Cavalier, Säzava, Czech Republic, of 3 cm in length, with an outer diameter of 6 mm and a wall thickness of 1 mm at room temperature in a solution of 70 vol .-% conc were , Sulfuric acid and 30 vol .-% Wasserstoffproxidlösung (30% in water) for one hour in an ultrasonic bath. The glass tubes were washed three times with distilled water and dried in an oven at 50 0 C overnight.

Under exclusion of UV light 600 mg silicone-polycarbonate membrane were in a rolled rim glass (product name SSP-M213, Company Specialty Silicone Products, Inc., New York, USA) with a solution of 18 mg of N, N'-diphenyl-1 , 4-phenylenediamine (Aldrich, Steinheim, Germany) in 10 ml of chloroform pa (Aldrich, Steinheim, Germany) and stirred until dissolution of the membrane. To produce the detection tube, the glass tubes were attached to one end by a Federarmpinzette on an adjustable in height by means of stepping motor fixture, product name BGS60 the company EAS GmbH, Rheinberg, Germany. With the help of this device, the glass tube at a rate of 36 cm min were "1 immersed in the prepared solution to a depth of 2.8 cm, and after 10 s at a speed of 22.5 cm min" 1 again from the solution pulled out. The inside and outside thus coated glass tubes were dried perpendicular for 30 min at room air. For the removal of the outer coating, the interior and exterior coated glass tube on the outer side were rubbed with a moistened with acetone, lint-free cloth. The detection tube thus prepared with a layer thickness of the coating of about 1 micron were suitable for the determination of nitrogen in gaseous samples.

The measurement cell used in this case for measurement consisted of a LED with 435 nm peak wavelength as a light source and a photodiode with integrated operational amplifier OPT-301 of the firm Burr-Brown (reference: GMS, Karlsruhe, Germany) as Photoempfän- ger. The analog voltage signal of the photodetector was measured using a 12-bit A / D

Converter module LTC 1293 (manufactured by Linear Technology) is converted into a digital voltage signal. The suction created by a miniature diaphragm pump NMP 015 B company KNF Neuberger, Freiburg, Germany, caused in the detection tube a flow of the gaseous sample of 1380 ml min "1, which by means of a mass flowmeter is au- ßerhalb the measuring cell located type F- 1 11 C-HAD-33-P (from Bronkhorst Hi-Tec, Ruurlo, the Netherlands) was determined. temperature and moisture content of the gaseous sample was directly after the outlet of the gas from the detection tube by means of a digital humidity and temperature Sensmitters SHT75 the company Driesen + Kern GmbH, Bad Bramstedt, Germany determined.

The reactivity of the detection tubes prepared to nitrogen dioxide was in dry gaseous samples having an average temperature of 24.7 0 C ± 1, 5 0 C and a volume fraction of nitrogen in synthetic air (20.5% O 2 in N 2 (Messer Griesheim GmbH , Krefeld, Germany)) was investigated between 2 ppm and 25 ppb. The nitrogen dioxide was removed from test gas (Messer Griesheim GmbH, Krefeld, Germany) and the desired concentration and volume flow by dilution with synthetic air with the help of mass flow controllers of the type F-201C-RAA-33-E of the company Bronkhorst Hi-Tec, Ruurlo, Netherlands, set.

It has been found that at the beginning of the measurement, the voltage signal of the photodetector linear change with time (see Fig. 9 and 10), ie the speed with which the voltage signal of the photoreceiver changed was at a given gas concentration in the initial region approximately constant. The speed with which the voltage signal of the photoreceiver changed, s was determined from the area of ​​maximum voltage change of -15 to -200 mV, not reaching the latter value times up to a measurement period of the 180th

There was a linear relationship between the speed with which the voltage signal of the photoreceiver changed, and the concentration of nitrogen dioxide found (see Fig. 11).

The regression parameter here is excellent with R 2 = 0.999. By dividing the voltage value of the photodetector during measurement by the voltage value of the photoreceptor prior to the measurement, the voltage values ​​in transmission values ​​could be converted. This was made possible by the high linearity between voltage signal and the light intensity of the photodetector. With the help of the obtained linear calibration it was possible to determine unknown concentrations of nitrogen dioxide in gaseous samples with high precision and reproducibility with the aid of the detection tube described for the detection of nitrogen dioxide. Due to the high sensitivity very short measurement time of about 180 s resulted in 25 ppb and 22 s at 2 ppm nitrogen dioxide. The detection tubes produced were stable on storage in light exit circuit and under an argon atmosphere over a period of one month. The coating material of the detection tubes used is stable in storage for a period of at least 1 year.

Example 2:

The production of the detection tubes was carried out as in Example 1 except that the loading was coating solution of 800 mg silicone polycarbonate membrane (product name SSP M213, Company Specialty Silicone Products, Inc. New York, USA), with a solution of 4 mg 4,4'-Dinonoxy-7,7-dimethoxy-indigo (Dr. G. Voss, University of Bayreuth, Germany) was added in 10 ml of chloroform pa (Aldrich, Steinheim, Germany) and stirred until dissolution of the membrane. The detection tube thus prepared with a layer thickness of the coating of about 2 micrometers were suitable for the determination of ozone in gaseous samples.

The measuring cell used for the measurements differed from the measuring cell, which was used in Example 1 in the used as the light source. At this point, an LED having a peak wavelength of 650 nm (product name ELD-650-523 Company Roithner Lasertechnik, Vienna, Austria) was used.

The reactivity of the detection tubes prepared to ozone was measured at dry gaseous samples having an average temperature of 22.9 0 C ± 1, 5 0 C and investigated a proportion by volume of ozone in air between 340 ppm and 25 ppb. It was also found to ozone, a linear relationship between the rate at which the voltage signal of the photoreceiver changed at the start of the measurement, and concentration. By means of the hereby obtained linear calibration it was possible to determine unknown concentrations of ozone in gaseous samples with the aid of the detection tube described for the detection of ozone. The coating material of the detection tubes used is stable in storage for a period of at least 6 months.

Claims

claims
1. A measuring device (10) for the optical determination of the concentration of at least one harmful gas in transmission, comprising a light-tight measuring cell (12) having a receptacle (14) in which a tube-shaped, at least partially light-transmitting detection means (16) which at least on its inner wall partially having a light-transmitting coating (18) with a prescribable layer thickness of at least one polymeric material having at least one, in this immobilized indicator substance is arranged, further comprising the detection means (16) comprising upstream or downstream of pumping or suction device (20) which directing a noxious gas stream through the detection means (16), and at least one light source (22) and at least one receiver means (24) which are arranged on one and / or more sides of the Detekti- onsmittels (16) by means of which in transmission, an absorption change in the indicator substance in response to the Zei t is measured, wherein the recipient medium (24) with an evaluation unit (26) is connectable.
2. Measuring device according to claim 1, characterized in that the coating (18) has a thickness in a range from 0.1 .mu.m to 1 mm.
3. Measuring device according to one of the preceding claims, characterized in that said detecting means (16) at its two ends (30.1, 30.2) with a gas-tight sheet (32.1, 32.2) is provided.
4. Measuring device according to one of the preceding claims, characterized gekennzeich- net that the receiver means is formed as a photodiode, phototransistor and / or photoresistor.
5. Measuring device according to one of the preceding claims, characterized in that the pumping and suction device (20) sucks in the harmful gas volume flow with a constant Vo-.
6. Measuring device according to one of the preceding claims, characterized in that it has a humidity and / or temperature sensor and / or a mass flow sensor (34).
7. Measuring device according to one of the preceding claims, characterized in that a wall (36) is at least partially provided the receptacle (14) having a reflective surface.
8. detection means according to one of claims 1 to. 3
9. A method for the optical determination of at least one harmful gas in transmission, wherein arranged with a constant volume flow of a harmful gas stream by one in a measuring cell (12) detecting means (16) is guided, which tung a coating (18) of at least one polymeric material comprises wherein at least one light beam by the detecting means (16) is guided, in which at least one indicator substance is immobilized, and wherein at least in a partial area, the speed of the measurable transmission or voltage change and / or rate of absorption change in approximately linear in the gas concentration runs.
10. The method according to claim 9, characterized in that the light beam at least twice by the detection means (16) is guided.
PCT/EP2006/008016 2005-08-20 2006-08-14 Measuring device for optical determination of toxic gas concentration by transmission WO2007022895A3 (en)

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DE102005039539.2 2005-08-20
DE200510039539 DE102005039539B3 (en) 2005-08-20 2005-08-20 Measuring device, for visually determining of concentration of pollutant gas in transmission, has light source and receiving means by means of which absorption change of indicator substance is measured in dependence upon time

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