WO2006117328A1

WO2006117328A1 - Method and device for detecting substances in aqueous gaseous media

Info

Publication number: WO2006117328A1
Application number: PCT/EP2006/061893
Authority: WO
Inventors: Niko Näther; Michael J. Schöning; Hartmut Henkel; Andreas Schneider; Jörg Berger; Rüdiger Emmerich
Original assignee: Sig Technology Ag
Priority date: 2005-04-29
Filing date: 2006-04-27
Publication date: 2006-11-09
Also published as: DE102005020459A1

Abstract

The invention relates to a method and device for quantitatively determining the concentration of hydrogen peroxide (H2O2) in the gas or vapor phase with at least one sensor, which is placed in direct contact with the medium to be analyzed. The aim of the invention is to enable the device and the method to be used for detecting hydrogen peroxide in vapor-containing or gaseous media and to be integrated on-line in the process sequence of the disinfection or sterilization whereby making the detection of the hydrogen peroxide concentration possible even at elevated temperatures, particularly between 100 °C and 300 °C. To this end, the invention provides that the sensor is designed in such a manner that molecules of the hydrogen peroxide are excited until they decompose, and that the sensor uses the heat resulting from this exothermic reaction for determining the H2O2 concentration. To this end, the sensor (1, 2) is provided in the form of a temperature sensor, which directly converts a change in temperature in the form of a change in resistance, voltage, current or power consumption for measuring the qualitative or quantitative hydrogen peroxide concentration.

Description

Method and device for the detection of substances in aqueous, gaseous media

The invention relates to a method and a device for the quantitative determination of the concentration of hydrogen peroxide (H2O2) in the gas or vapor phase with at least one sensor, which is brought into direct contact with the medium to be investigated.

For sterilization and disinfection in the gas phase or in liquids, reactive substances, in particular hydrogen peroxide, since this is a complete wetting of the sterilization or disinfection material is guaranteed. For optimal sterilization or disinfection with, for example, hydrogen peroxide from the gas phase, an aerosol of air and hydrogen peroxide is often heated, wherein the hydrogen peroxide passes into the gas phase or the liquid hydrogen peroxide is evaporated, which is then mixed with an air stream. Thereafter, the gaseous stream comes directly into contact with the medium to be sterilized. The successful sterilization or disinfection is ensured on the one hand by the temperature of the sterilization or disinfection mixture and on the other hand by the resulting OH radicals. The sterilization or

Disinfection method with occurring, for example, in the gas phase hydrogen peroxide is nowadays, inter alia, for food packaging, medical devices, medical packaging, pharmaceutical Products and packaging generally used. An enormous advantage of this "gas phase sterilization or disinfection" lies in the simple removal of residues of the sterilizing agent with superheated steam.

A principal problem with such Sterilisationsbzw. Disinfection processes is that the effectiveness of the sterilization or

Disinfection procedure among other things crucially related to parameters such as the contact time, the temperature, the pretreatment of the material and the initial concentration of hydrogen peroxide. Therefore, it is necessary to allow the qualitative and quantitative detection of the hydrogen peroxide concentration immediately before contact with the actual sterilization or disinfection, in order to ensure the most accurate adjustment of the hydrogen peroxide concentration after the sterilization or disinfection process at Gut.

In addition to amperometric and potentiometric detection methods for detecting the H ₂ C> ₂ concentration in liquids with the aid of enzymes (eg catalase and horseradish peroxidase), special membranes (eg Nafion, poly-HEMA) or porous materials (eg solid-state electrolytes, nanostructured silicon), there are detection methods such as titration, test strip photometry, semiconductor gas sensors and NIR spectroscopy for determining the hydrogen peroxide concentration in the gas phase.

In the titration method, for example, a defined amount of gas must be sucked in and cooled, which is then passed into a glass frit, in the a defined amount of bidistilled water is submitted. After this "gas scrubbing", the resulting solution is mixed with 20% sulfuric acid After addition of a certain amount of potassium iodide and ammonium molybdenum solution, titration is carried out with the addition of sodium thiosulfate solution "colorless". From a resulting equation, the mass of hydrogen peroxide in the solution can then be calculated. This mass specification can be used to calculate the concentration in the intake gas. A disadvantage of this method is the relatively high expenditure on equipment and the "off-line" methodology, which does not allow continuous recording of the hydrogen peroxide concentration (research project: "Durability extension of dairy products by optimizing the activation of germs in food and packaging materials", Technical University of Munich, 2004 ).

Another variant describes an apparatus for "on-line" determination of the concentration of hydrogen peroxide vapor during sterilization or disinfection.It is based on the use of known metal-oxide-semiconductor sensors (eg of commercially available Snθ ₂ gas sensors or sensors based on TiO ₂ , Fe ₂ O ₃ , ZnO, etc.) [DE 198 55 120 Al; US Pat. No. 5,608,156; I. Taizo, A. Sinichi, K. Kawamura, J. Pharmaceutical Sci. Technol , 52 (1998) 13] In such semiconductor gas sensors, a heated semiconductor, which is heated to 200 to 400 ^° C. operating temperature, reacts to reducing or oxidizing gases with a change in conductivity Procedure is that the sensor signal is strongly influenced by the humidity and the Temperature of the analyte and must be corrected with a set of previously recorded and specific correlation data. Consequently, such a sensor can only be used if the environmental variables temperature and humidity are known or measured constantly and / or separately with sensors of a different type and associated other measuring signals. This links the use of a more sophisticated measuring electronics. Furthermore, it is not known in the proposed arrangement how the flow velocity affects the sensor signal.

Another method represents near-infrared (NIR) spectroscopy, in which a light beam of known wavelength and intensity distribution is passed through the analyte to be examined and then recorded by a detector in such a way that the absorption of the analyte can be calculated. This very fast method, which has a very low detection limit, is used, for example, by the company GuidedWave in an "H ₂ O ₂ vapor monitor." In this apparatus, the gas to be examined is taken out of the process and then in a measuring unit. " measured off-line. A disadvantage of this method, however, is the need for a high and cost-intensive, equipment and the need for very long light paths through the analyte (not infrequently 10 m), so that an integration into existing process equipment, which include an additional sterilization or disinfection unit is made difficult, and also makes a continuous "online" analytics difficult to realize. Another way to determine vapor phase H ₂ O ₂ is the use of test paper, known as a test strip photometry method. This procedure is performed by means of a test paper wherein the test paper has been specially treated with a chemical so that it changes color upon contact with H ₂ O ₂ vapor. By the subsequent optical color detection, the concentration of H ₂ θ2 vapor can be determined. However, such chemoindicators or test strips can only be used as "disposable" sensors for one sterilization process and therefore represent relatively expensive consumables. Moreover, it is not possible with them to determine the course of sterilization and thus the time-dependent measurement of the various parameters during sterilization Another disadvantage is the duration of the color change process (about 1-12 min., [S. Corveleyn, GMR Vandenbossche, JP Remon, Pharmaceutical Research, 14 (1997), 294; VM Ostrovskaya, YA Zolotov, AV Davydov, J. Anal 54 (1999), 764], ie the Anpsrechzeit and the fact that these sensors can not be used at elevated operating temperature (> 100 ⁰ C) and that in most cases the required concentration ranges is not reached ..

It is therefore an object of the present invention to reduce or avoid the disadvantages described above for the detection of hydrogen peroxide in the gas or vapor phase. A corresponding device or a method for the detection of hydrogen peroxide to

- can be used in vaporous or gaseous media, - can be integrated "on-line" in the process of disinfection or sterilization,

- The detection of the hydrogen peroxide concentration even at elevated temperatures, in particular between

Allow 100 ⁰ C and 300 ⁰ C.

The object is achieved by a method or a device according to the totality of the features of claims 1 and 5, respectively. Further expedient or advantageous embodiments can be found in the subclaims referring back to one of these claims.

The invention is described in more detail below with reference to three different transducer variants for detecting the hydrogen peroxide concentration in the vapor phase:

Version 1 :

A possible transducer principle is the use of a catalytically active material such as platinum, copper, copper-nickel compounds, rhodium, Rhutenium, Hexacyanoferraten etc., in particular a manganese-containing compound, in combination with a physical sensor. This used as a detector physical sensor can, for example Thermocouple, resistance thermometer, thermistor, pellistor, NTC, PTC, etc., but in particular a stainless steel sheathed thermocouple or

RTDs. The catalytically active material is deposited or applied to the physical transducer for this purpose. The deposition or binding of the catalytically active material may be physical or chemical nature. Thus, for example, the catalytically active material can be separated from the gas phase by known CVD and / or PVD methods. In addition, methods of thin-film or thick-film technology can generally be used. Alternatively, the deposition of the catalytically active material from a liquid, for example as Precipitation done or by conventional manufacturing techniques such as gluing, soldering, welding or the like. be attached.

If an exothermically reacting gas now reaches the surface of the catalytically active material, the dissociation energy is reduced, so that, for example, hydrogen peroxide would decompose even at room temperature. This decay releases heat which causes a temperature increase on the temperature sensor acting as a physical transducer. This temperature increase can be detected directly in the form of a change in resistance, voltage, current or in a change in the power consumption of the detector and quantitatively or qualitatively (via a calibration) be assigned to the existing hydrogen peroxide concentration. A great advantage of this method is the high temperature resistance of the used cataltic layer, ie the detector can be used even at elevated process temperatures during sterilization in real time operation. Furthermore, temperature fluctuations in the analyte do not influence the exothermic reaction caused by the catalytic reaction and thus the sensitivity of the sensor. Variant 2 :

Another possible approach is to use a calorimetric gas sensor, such as a pellistor, NTC, PTC, etc., particularly a hot wire sensor that is suitable for the detection of exothermically reactive gases, despite or because of its insufficient selectivity. Such a calorimetric sensor exists realized from a heated element, usually by a current flow in a conductor whose conductivity varies depending on the temperature. If under normal conditions in the gas phase exothermically reactive gases are stable, takes place at the heated element, an energy transfer to the single gas molecule, which is sufficient to stimulate the molecule to decay. The heat released in the exothermic decomposition then leads to a temperature increase of the heated element, which in turn leads to a change in conductivity of this element. This conductivity change is used directly as a measurement signal and can be detected according to the above variants as current, voltage, resistance, conductivity change or as a change in frequency, the optical properties, the waveform or as a change in power consumption of the sensor. Since it is dispensed with the additional use of a catalyst, no selective detection of the hydrogen peroxide concentration can take place. On the other hand, taking into account the exact process parameters during the disinfection or sterilization process, it is possible to carry out an indirect qualitative and quantitative calibration of the existing hydrogen peroxide concentration on the basis of a fixed, defined parameter set. Variant 3:

Another possible approach involves the use of thermocouple-like arrangements whose temperature measuring point is in direct contact with the medium to be investigated (H2O2). If one of the metals or both metals of the temperature-sensitive metal pairing of the thermoelement-like arrangement is one or more catalytically active materials, such as Fe / CuNi, NiCr / Ni, PtRh / Pt, NiCr / CuNi, IrRh / Ir, Wo / Ta , NiCrSi / NiSiMg, etc., however, especially around Cu / CuNi, decomposes due to the catalytic effect of the exothermic gas and the heat energy released is detected directly as a temperature increase at the thermocouple. This temperature increase can be detected directly in the form of a resistance, conductivity, impedance, voltage, current change or in a change in frequency, the optical properties, the waveform or as a change in power consumption of the detector and qualitatively or (via a calibration ) are quantitatively assigned to the existing hydrogen peroxide concentration. A great advantage of this method is the high temperature resistance of the catalytic arrangement used, ie, the detector can be used even at elevated process temperatures during sterilization in real-time operation. Furthermore, temperature fluctuations in the analyte do not influence the exothermic reaction caused by the catalytic reaction and thus the sensitivity of the sensor. The abovementioned solutions (variants) can be used individually, linked together in the form of an array and / or together with one or more temperature sensors of identical and / or different construction, in order to compensate for possible interfering influences due to the temperature or moisture of the analyte.

The invention will be described in more detail below with reference to preferred embodiments. In the drawing show:

1 shows a first embodiment of a device according to the invention in a schematic representation,

Fig. 2 shows a second embodiment of a device according to the invention in a schematic representation and

Fig. 3 shows a further embodiment of a device according to the invention in a schematic representation.

Spaced sensors 1 and 2 of the previously explained in more detail and thus particularly preferred variants can be mounted according to FIG. 1 in a closed on one side and / or on both sides, partially or completely open vessel 3. In this case, either 1 and / or 2 represents an arbitrary sensor of the variants presented. In addition, sensor 1 or 2 can also represent a further temperature sensor. The sensors are at a defined distance, in the case of sensor 1 in a defined Li or in the case of Sensor 2 mounted at a defined distance from L ₂ of the wall of the vessel 3, or protrude in the illustrated case of the sensor 1 with the defined length Li and of the sensor 2 with the defined length L ₂ in the vessel 3 into it. The sensors 1, 2 are arranged at a defined distance from each other.

According to FIG. 2, the sensors 1 'and 2' can also be attached to a vessel 3 'closed on one side and / or on both sides, partially or completely opened. The sensors 1 ', 2' are located in cells 4 and / or 5 which are arranged at a defined distance from one another and which are connected to the vessel 3 'via an opening (not shown) of a defined cross-section which ensures a gas exchange are.

Here, too, sensor 1 'and / or sensor 2' can represent a sensor described above in more detail variants or else also a further temperature sensor, as already described for FIG. 1 or as explained below for FIG. 3. The sensors 1 'and / or 2' can protrude significantly into the cells 4 or 5. Furthermore, a compound 6 with a defined cross section between the cells 4 and 5 may be attached. Furthermore, the cells may additionally be equipped with heating elements or channels (not shown) for heating.

Fig. 3 corresponds substantially to the embodiment of Fig. 2 with the change that in the case of a flowing medium, the vessel 3 '' includes a change in the diameter of internals 7. This change in diameter is constructed so that the cross section H of the vessel in a defined manner to the cross-section Hi in the region of the cell 4 'and / or on the cross-section H ₂ in the region of the cell of the cell 5' reduced. In or on the cross-sectional changes, an opening 8 with a defined cross-section Ai in the region of the cell 4 'or with a defined cross-section A ₂ in the region of the cell 5' in such a manner that a gas exchange between the vessel 3 '' and each cell 4 ', 5' can take place. Again, the cells 4 'and 5' again with a connection channel 6 are in communication.

A further, not shown exemplary embodiment takes into account that, in addition to the embodiments according to FIG. 1, 2 or 3, an additional reference system with the same structure according to FIG. 1 and / or 2 and / or 3 is constructed, which is acted on by a reference medium. This is done in such a way that in addition to the device with the medium to be examined another device of the embodiments of FIG. 1 and / or 2 and / or 3 is constructed, in or through which a medium (eg gas stream) passed other composition becomes, so that from the measurement results of both systems, a difference signal can be detected. In this case, the reference arrangement may be constructed as a separate system and / or be integrated into the illustrated embodiments in such a way that an arbitrary sensor of the described variants or a temperature sensor is supplied with a reference gas.

Claims

PATENT AT SPRU

A method for the quantitative determination of the concentration of hydrogen peroxide (H2O2) in the gas or vapor phase with at least one sensor, which is brought into direct contact with the medium to be examined, characterized in that the sensor is designed so that molecules of hydrogen peroxide for Decay and that the sensor uses the heat generated during this exothermic reaction to determine the H2O2 concentration.

2. The method according to claim 1, characterized in that a catalytically active material is brought in the vicinity of the at least one sensor, which reduces the dissociation energy of the exothermic gas when it comes into contact with the surface, so that a decomposition of the hydrogen peroxide can also be carried out at low temperatures ,

3. The method according to claim 1, characterized in that for determining the H ₂ C> ₂ concentration, an active sensor is used, the energy supplied stimulates the decomposition of the molecules of hydrogen peroxide.

4. An apparatus for the quantitative determination of the concentration of hydrogen peroxide (H2O2) in the gas or vapor phase with at least one sensor which is in direct contact with the medium to be investigated, characterized in that the sensor (1, 2, 1 ', 2' , 1 ", 2") is a temperature sensor, which is a

Temperature change immediately converts into an evaluable size for measuring the quantitative or qualitative hydrogen peroxide concentration.

5. The device according to claim 4, characterized in that the sensor (1, 2, 1 ', 2', 1 ", 2") is a temperature sensor, which is a temperature change directly in the form of a change in resistance, impedance, voltage, of the current, the power consumption, the frequency, the signal shape or the optical properties for measuring the quantitative or qualitative hydrogen peroxide concentration.

6. Apparatus according to claim 4 or 5, characterized in that the sensor (1, 2, 1 ', 2', 1 '', 2 '') is arranged in spatial proximity to a catalytically active substance.

7. The device according to claim 6, characterized in that the sensor (1, 2, 1 ', 2', 1 '', 2 '') is a thermocouple.

8. Device according to claim 6, characterized in that the sensor (1, 2, 1 ', 2', 1 ", 2") is a resistance thermometer.

9. Device according to claim 6, characterized in that the sensor (1, 2, 1 ', 2', 1 ", 2") is a thermistor.

10. The device according to claim 6, wherein the catalytically active substance consists of platinum, copper, copper-nickel compounds, rhodium, ruthenium, hexacyanoferrate or a manganese-containing compound.

11. Device according to claim 5, characterized in that the sensor (1, 2, 1 ', 2', 1 ", 2") is a calorimetric gas sensor whose conductivity changes as a function of temperature.

12. Device according to claim 11, wherein the sensor (1, 2, 1 ', 2', 1 ", 2") is a pellistor.

13. The device according to claim 5, characterized in that the sensor (1, 2, 1 ', 2', 1 ", 2") is a thermocouple, wherein one of the metals or both metals of the temperature-sensitive metal pairing of one or more catalytically active materials.

14. The device of claim 13, wherein the catalytically active materials are CuNi, Fe, Ni, NiCr, Pt, PtRh, NiCr, IrRh, Ir, Wo, Ta, NiSiMg or NiCrSi.

15. Device according to claim 5, characterized in that the sensors (1, 2, 1 ', 2', 1 '', 2 '') are used individually or directly linked in the form of an array.

16. Device according to one of claims 5 to 15, characterized in that two sensors (1, 2, 1 ', 2', 1 '', 2 '') are present, which are arranged at a defined distance from each other in the medium to be examined ,

17. The apparatus according to claim 16, characterized in that the two spaced-apart sensors (1, 2, 1 ', 2', 1 '', 2 '') in an at least partially closed measuring section (3, 3 ', 3' ') are arranged.

18. Device according to claim 16 or 17, wherein the arrangement of the sensors (1, 2, 1 ', 2', 1 '', 2 '') is chosen such that a reliable contact with the medium to be examined takes place.