DE102022128472A1 - Arrangement and method for determining the concentration of one or more substances in a liquid or gaseous medium - Google Patents

Abstract

An arrangement for determining the concentration of one or more substances in a liquid or gaseous medium has a measuring chamber into which the medium can be introduced or through which the medium can flow, as well as a number of measuring channels, each of which is formed by a light source and one or more detectors assigned only to this light source. The number of measuring channels corresponds at least to the number of a selection of characteristic absorption peaks that is at least required to determine the concentration of the one or more substances. Each measuring channel is designed in such a way that it measures an absorption of optical radiation in the liquid or gaseous medium in the measuring chamber for a different characteristic absorption peak of the selection, in that the light source of this measuring channel emits narrow-band radiation that corresponds to a wavelength of the respective absorption peak. The arrangement enables selective analysis of even complex samples in the sub-ppb range, can be implemented cost-effectively and can be adapted modularly to the corresponding application.

Description

Technical application area

The present invention relates to an arrangement for determining the concentration of one or more substances in a liquid or gaseous medium which have characteristic absorption peaks when illuminated with optical radiation. The invention also relates to a method for determining the concentration using such an arrangement.

The analysis of liquid or gaseous media with regard to the concentration of individual substances in these media plays an important role in many technical and scientific applications. Many substances have characteristic optical absorption peaks that form a fingerprint of the respective substance, so that the substances can be clearly identified or determined using optical absorption spectroscopy, for example. Photoacoustic spectroscopy can also be used to determine the concentration of substances in a liquid or gaseous medium. In photoacoustic spectroscopy, the specific light absorption at an absorption peak creates a pressure change or acoustic wave in the medium, which is recorded with a detector and converted into an electrical signal. A microphone, for example, can be used as a detector. The recorded pressure change is a measure of the concentration of the corresponding substance. However, the measurements always require the wavelength of the incident optical radiation to be adapted to the substance or substances to be measured. The required wavelength can be set for this purpose, for example, using a spectral filter or by using a tunable laser.

State of the art

For example, the EP3508836B1 a photoacoustic gas sensor in which radiation from a broadband IR light source is passed through a bandpass filter into a measuring chamber containing the gas to be measured. The optical bandpass filter only allows a certain part of the light spectrum to pass through. The central wavelength is adjusted to the absorption maximum of the gas to be detected. By temporally modulating the IR light source up to 100 Hz, a sound wave is created within the measuring chamber by the absorption of the radiation in the gas, which is measured by a highly sensitive pressure sensor on the measuring chamber and is a measure of the concentration of the absorbing gas. However, the gas sensor in this arrangement can only detect a gas with an absorption maximum at the corresponding filter wavelength.

From the DE 102021108745 A1 An arrangement for multispectral light emission and a multispectral sensor equipped with it are known, with which a simple and quick adjustment or change of the emitted wavelengths is possible. This arrangement has a broadband light source in conjunction with a filter array made up of several spectral filters and a switching device for controlling the passage of the light emitted by the light source through individual filters of this filter array. This enables an adjustment or variation of the wavelength or spectral distribution of the emitted optical radiation according to the number and characteristics of the different filters of the filter array. This allows the spectral distribution of the emitted light to be adapted for the respective application, for example to characteristic absorption peaks in optical absorption spectroscopy or photoacoustic spectroscopy for determining the concentration of substances in a medium. The arrangement has one or more broadband light sources, a filter array, a switching device and a common detector.

Especially for the selective analysis of complex samples in the sub-ppb range, many substances in a liquid or gaseous medium must be determined with high sensitivity in terms of their concentration. This should be done as cost-effectively as possible. One example is wine aroma analysis, in which a large number of aromatic substances in the wine are to be determined. The object of the present invention is to provide an arrangement and a method for determining the concentration of one or more substances in a liquid or gaseous medium, which can be implemented cost-effectively and adapted to the respective application.

Description of the invention

The object is achieved with the arrangement and the method according to patent claims 1 and 12. Advantageous embodiments of the arrangement and the method are the subject of the dependent patent claims or can be taken from the following description and the embodiments.

The proposed arrangement is designed to determine the concentration of one or more substances, in particular pure substances, in a liquid or gaseous medium, which have characteristic absorption peaks when illuminated with optical radiation. The arrangement comprises at least one measuring chamber into which the liquid or gaseous medium can be introduced or through which the liquid or gaseous medium can flow, and a number of measuring channels, which are each formed by a light source and one or more detectors assigned only to this light source. The number of measuring channels corresponds at least to the number of a selection from the characteristic absorption peaks that is at least required to determine the concentration of the one or more substances in the liquid or gaseous medium. This takes advantage of the fact that in many cases not all of the characteristic absorption peaks of this substance have to be measured in order to clearly identify and determine the concentration of this substance, but measuring a smaller number of absorption peaks, i.e. a selection from the characteristic absorption peaks, is sufficient. Each measuring channel is designed in such a way that it measures an absorption of optical radiation in the liquid or gaseous medium in the measuring chamber for one of the characteristic absorption peaks of the selection. For this purpose, the light source of this measuring channel is selected so that it emits narrow-band radiation at a wavelength that corresponds to the wavelength of the respective absorption peak. Narrowband means that the bandwidth of the emitted radiation is small enough to detect only one of the characteristic absorption peaks of the substances in the liquid or gaseous medium. The bandwidth of the emitted radiation of the respective light source is preferably < 300 nm, particularly preferably < 100 nm. Each measuring channel is designed to measure a different characteristic absorption peak of the selection made.

In the present patent application, the light source is understood to mean a light-emitting unit that emits narrow-band optical radiation at the corresponding wavelength. This can be a single light emitter, for example a laser diode or a light-emitting diode (LED), which emits the narrow-band radiation directly. However, the light source can also be formed by a broadband emitting light emitter with one or more upstream spectral filters, with the filter or filters then having the corresponding narrow-band passband at the desired wavelength. Additional optical elements, for example lenses or optical fibers, can also be part of the light source.

The proposed design of the arrangement allows it to be easily adapted to the respective measurement task, i.e. it can be specially designed for the substances to be determined in the liquid or gaseous medium by selecting the required number and emission wavelength of the measuring channels. This modular principle and the independence of the individual measuring channels enable a cost-effective and simple structure. The arrangement can also be used to measure more complex samples cost-effectively, for example in wine aroma analysis.

In the proposed arrangement, each measuring channel is designed for a specific wavelength. One or more detectors with different measuring principles can be used per measuring channel. A combination of photoacoustic spectroscopy (PAS) and absorption spectroscopy is particularly preferred in the proposed arrangement. It is of course also possible to implement only one measuring principle in the respective measuring channel, for example only photoacoustic spectroscopy or only absorption spectroscopy. In principle, different types of detectors can be used in measuring channels, for example microbolometers, pyroelectric detectors, resistive detectors (MOX), thermal conductivity detectors (TCD), catalytic converters, photodetectors or pressure detectors or microphones. Depending on the light source and detector, the detectors can also be integrated in the light source or in the light emitter. This applies in particular to types of detectors that require a heating element (e.g. MOX, TCD, pellistor). Depending on the detector, these are arranged inside the measuring chamber, as in the case of a microphone or pressure sensor, but can also be arranged outside the measuring chamber, as in the case of a photodetector. A photodetector can of course also be arranged inside the measuring chamber. The measuring chamber itself must be designed to be permeable to the optical radiation at least at the corresponding coupling or decoupling points.

In the preferred embodiment, the measuring chamber is tubular and connected to a pump, via which the liquid or gaseous medium to be measured is sucked or pumped through the measuring chamber. The corresponding measuring channels are then arranged next to one another along the tubular measuring chamber. In a special embodiment, the tubular measuring chamber, which can also have a non-circular, for example rectangular, cross-section, has several tubular extensions along its length, each of which extends transversely to the longitudinal axis of the measuring chamber and into which the medium to be measured diffuses as it flows through the measuring chamber. Such extensions, which each form separate measuring volumes, are also possible with a non-tubular measuring chamber. The measuring channels are then arranged on these extensions, as shown in more detail in a later embodiment. At the transition to these extensions, A membrane or a filter must be present that only allows certain substances to diffuse into the mixture. This allows a pre-separation of the substances.

In an advantageous embodiment, at least one of the light emitters of the measuring channels is formed by a heating element, i.e. a radiant heater that emits radiation in the IR range. In a particularly preferred embodiment, this radiant heater is simultaneously used as a thermal conductivity sensor by detecting its electrical resistance change in the respective measuring channel. The measuring channel has a diffusion opening at the corresponding point in the area of this light emitter, through which a small part of the medium flowing through the measuring chamber diffuses out and is guided over the light emitter. The diffusion opening can also be implemented by an optical filter if this is designed accordingly, for example as a plasmonic filter. This means that CO ₂ or hydrogen, for example, can be detected with this light emitter. Alternatively, another sensor, for example to form a MOX sensor, a thermal conductivity sensor or a heat tone sensor, can be arranged near the light emitter designed as a radiant heater, which is then heated via the light emitter, i.e. does not require its own heating element. In this case, the medium flows over this additional sensor, so that _CO2 or hydrogen, for example, can be detected.

The design described above, in which a radiant heater is used as a light emitter and is simultaneously used as a thermal conductivity sensor or in conjunction with an additional MOX sensor, thermal conductivity sensor or heat tone sensor, can also be used independently of the present arrangement as a measuring device, which, for example, comprises only one light source or also an arrangement of several light sources or measuring channels that share a common detector.

In the proposed method, the proposed arrangement is designed in such a way that the individual measuring channels are adapted to the selection of absorption peaks of the substances to be measured in terms of the number and light sources. The liquid or gaseous medium is then introduced into the measuring chamber or sucked or pumped through the measuring chamber. The detectors of the measuring channels are used to measure the absorption at the corresponding wavelength or the respective characteristic absorption peak in order to derive the concentration of the corresponding substances. In order to avoid mutual interference between the individual measuring channels, a temporally serial measurement is preferably carried out in which the individual measuring channels are operated at different times so that only one measuring channel is active at a time, i.e. only the light source of this one measuring channel is switched on at a time. In another embodiment, which requires the use of photoacoustic spectroscopy as a detection principle, the light sources of the individual measuring channels are modulated with different frequencies in order to generate acoustic waves with different frequencies that do not interfere with each other. This also avoids mutual interference between the individual measuring channels when they are operated at the same time.

The proposed arrangement and the associated method can be used in many areas of application, for example in medicine, the environmental sector, process engineering and civil security. This includes, for example, the analysis of industrial processes and parameters (process monitoring), quality assurance, early fire detection, aroma analysis, the detection of off-odors, breath gas analysis, security applications, environmental analysis, and use as an electronic nose or electronic tongue. This is of course not an exhaustive list.

Short description of the drawings

• 1 ein Beispiel für charakteristische Absorptionspeaks von EtOH und Ethylacetat;
• 2 ein Beispiel für charakteristische Absorptionspeaks von CO und CO₂;
• 3 ein erstes Beispiel für eine Ausgestaltung der vorgeschlagenen Anordnung;
• 4 ein Beispiel für eine besondere Ausgestaltung eines Messkanals;
• 5 ein weiteres Beispiel für eine besondere Ausgestaltung eines Messkanals;
• 6 ein weiteres Beispiel für eine Ausgestaltung der vorgeschlagenen Anordnung;
• 7 ein weiteres Beispiel für eine Ausgestaltung der vorgeschlagenen Anordnung;
• 8 eine schematische Darstellung einer zeitversetzten Betriebsweise der einzelnen Messkanäle bei einer Ausgestaltung der vorgeschlagenen Anordnung;
• 9 eine schematische Darstellung einer Ansteuerung unterschiedlicher Messkanäle mit unterschiedlicher Frequenz;
• 10 zwei weitere Beispiele für die Ausgestaltung eines Messkanals;
• 11 eine weitere beispielhafte Ausgestaltung der vorgeschlagenen Anordnung; und
• 12 eine beispielhafte Realisierung der Lichtquellen sowie des weiteren Sensors bei der Ausgestaltung der 5.

The proposed arrangement and the associated method are explained in more detail below using exemplary embodiments in conjunction with the drawings. Here:

• 1 an example of characteristic absorption peaks of EtOH and ethyl acetate;
• 2 an example of characteristic absorption peaks of CO and CO ₂ ;
• 3 a first example of a design of the proposed arrangement;
• 4 an example of a special design of a measuring channel;
• 5 another example of a special design of a measuring channel;
• 6 another example of a design of the proposed arrangement;
• 7 another example of a design of the proposed arrangement;
• 8th a schematic representation of a time-delayed operation of the individual measuring channels in an embodiment of the proposed arrangement;
• 9 a schematic representation of a control of different measuring channels with different frequencies;
• 10 two further examples for the design of a measuring channel;
• 11 a further exemplary embodiment of the proposed arrangement; and
• 12 an exemplary realization of the light sources and the additional sensor in the design of the 5 .

Ways to implement the invention

The proposed arrangement uses the fact that individual substances have one or more characteristic optical absorption peaks (so-called fingerprint) to determine individual substances in a liquid or gaseous medium, by means of which they can be clearly identified and by means of which their concentration in a medium can also be determined. 1 shows an example of characteristic absorption peaks of EtOH (ethanol) and ethyl acetate. The left-hand part of the image shows the characteristic absorption peaks of ethanol, and the right-hand part shows the characteristic absorption peaks of ethyl acetate. To distinguish between these two substances, a measurement at three different wavelengths is sufficient, namely at 3.4 µm, 8 µm and 9.4 µm. With the proposed arrangement, the concentrations of these two substances in a liquid or gaseous medium can therefore be determined using three measuring channels, each of which has a narrow-band light source with a central wavelength of 3.4 µm, 8 µm and 9.4 µm. The concentrations of the two substances can then be determined using the absorption strength recorded by the detector of the respective measuring channel and the ratio of this absorption strength at the three wavelengths. The proposed arrangement and the associated procedure assume that the individual characteristic absorption peaks of the substances to be determined are known.

2 shows another example of characteristic absorption peaks of CO (carbon monoxide) and CO ₂ (carbon dioxide). As can be seen from the left-hand part of the figure, CO has a characteristic absorption peak at a wavelength of 4.5 µm. From the right-hand part of the figure it can be seen that CO ₂ has a characteristic absorption peak at a wavelength of 4.2 µm. To differentiate and determine the concentration of these two substances, measurement at two wavelengths (4.5 µm and 4.2 µm) is therefore sufficient. For this purpose, the proposed arrangement has only two measuring channels for these two wavelengths.

3 shows an example of a possible design of the proposed arrangement. The measuring chamber 5 is tubular. The individual measuring channels (Ch1, ... Chx) are arranged next to one another along the measuring chamber. In this example, each measuring channel (Ch1, ... Chx) is formed by a light source (1(1), ... 1(x)) and a detector unit (2(1) ... 2(x)). Each light source (1(1), ... 1(x)) is designed for a specific wavelength that corresponds to the wavelength of a characteristic absorption peak of the substance to be determined. The individual light sources (1(1), ... 1(x)) can each be formed by a narrow-band light source (e.g. laser diode, LED) or a broadband light source with one or more upstream optical filter(s). The detector unit (2(1) ... 2(x)) can comprise one or more detectors. An optical absorption detector and/or a PAS detector can be used as a detector, for example. The individual measuring channels (Ch1, ... Chx) can be arranged modularly next to each other.

The media passed through the measuring chamber 5 are not converted in the respective measuring channel. The detectors can be arranged inside and/or outside the measuring chamber 5. During the measurement, the sample is sucked through the measuring chamber by a pump 6 using a sampling system 4 from a sample reservoir 3. While the sample flows through the measuring chamber 5, the measurement is carried out using the individual measuring channels.

The light sources (1(1), ... 1(x)) of the measuring channels (Ch1, ... Chx) can be designed in different ways. 4 shows an example of a specially designed measuring channel, which in turn is designed for a specific wavelength. In this example, a heating element 10 is used as a broadband IR light emitter. This heating element 10 is combined with an optical filter 11, which only allows optical radiation at the corresponding wavelength to pass through. In this example, the heating element 10 is also used as a detector. For this purpose, diffusion of the medium flowing through the measuring chamber 5 is made possible via corresponding diffusion openings 12 on the measuring chamber 5 over the heating element 10. By measuring the resistance on the heating element 10, this can be used as a thermal conductivity detector in order to detect, for example, CO ₂ or hydrogen. The heating element 10 thus serves both as an IR emitter and as a thermal conductivity detector. An optical absorption detector 7(1) is opposite the heating element 10 on the measuring chamber 5. Furthermore, a microphone 8(1) is arranged within the measuring chamber 5 near the point at which absorption takes place in order to detect, in addition to the optical In addition to the chemical absorption measurement, a PAS measurement can also be carried out.

5 shows an alternative design to 4 , in which the heating element 10 is not used as an additional detector, but rather another sensor 10a next to or below the heating element 10. This additional sensor 10a can be, for example, a MOX sensor, a thermal conductivity sensor or a heat tone sensor (each without its own heating element), which is heated via the heating element 10 used as an IR emitter. In this example, the medium emerging via the diffusion opening 12 thus flows over this additional sensor 10a in order to detect, for example, CO ₂ or hydrogen.

6 shows a further exemplary embodiment of the proposed arrangement, in which the measuring chamber is again tubular and the individual measuring channels (Ch1, ... Chx) are arranged along this measuring chamber. Here, too, the medium is sucked through the measuring chamber via a pump 6. In this example, the individual measuring channels (Ch1, ... Chx) each have a corresponding light source, an opposite optical absorption detector (7(1), ... 7(x)) and/or a microphone (8(1), ... 8(x)) as a PAS detector and are arranged along the horizontally arranged measuring chamber.

The measuring chamber itself can also have special tubular attachments designed for the measurement, as in the example of the 7 is shown. These attachments along the tubular measuring chamber form separate measuring volumes, at each of which the measuring channels are arranged. The medium is in turn preferably sucked in from a reservoir via a pump. The concentration equalization in the individual attachments takes place via diffusion through a membrane and/or a filter (9(1) ... 9(x)). Optionally, a gas-selective membrane or a gas-selective filter, for example made of thermoplastic polycondensate, such as PEEK, PEI, or of a fluoropolymer, such as FEP, ECTFE or PFA, can also be integrated into the respective attachment in order to increase the selectivity of the measurement. Such a membrane or such a filter can also be attached to the diffusion openings 12 of the embodiments of the 4 and 5 The membrane or filter can then be used - in the case of a gaseous medium - for pre-separation in the gas phase, or - in the case of a liquid medium - to measure gas dissolved in the liquid. The individual measuring channels each have a light source and one or more detectors, as was already apparent from the previous embodiments.

If several measuring channels with PAS detectors are used and the light in the individual measuring channels is modulated with the same frequency f(1), there is a risk of mutual interference between the individual channels, since the acoustic waves generated may interfere with each other. In one embodiment of the proposed method, the individual measuring channels are therefore operated one after the other in this case, so that at a certain point in time (t(1), ... t(x)) only one measuring channel is active, i.e. only one light source is switched on. This is shown schematically in 8th The individual measuring channels can be operated in any order.

Alternatively, the light sources of the individual measuring channels can also be modulated with different frequencies (f(1), ... f(n)) when using PAS detectors. This enables the simultaneous operation of all measuring channels, so that all measuring channels are active at any one time, since acoustic waves with different frequencies do not interfere with each other. This is shown schematically in 9 for two measuring channels Ch1, Ch2, which schematically shows the modulation signals for the light sources of the two channels Ch1, Ch2 in the right-hand part of the figure. The acoustic waves induced by this do not interfere with each other, as they are modulated differently. With additional electronics, the interfering signal of the other channel can be filtered out at each of the detectors 8(19, 8(2). This mode of operation can also be combined with the mode of operation of the 8th be combined.

When using photodetectors, i.e. the direct measurement of the optical absorption of the light emitted by the light source, measurements can be made both in reflection and in transmission. This is shown in the two partial figures of the 10 for the different designs already described above. In this example, the respective measuring channel has two photodetectors 7 for each light source 1. Only the absorption detector on the opposite side requires direct irradiation and must be arranged opposite the light source 1. The second detector measuring in reflection can be arranged next to the light source 1 on the same side of the measuring chamber or the measuring volume, as shown schematically in the two partial figures.

11 finally shows an exemplary embodiment of the proposed arrangement, in which the PAS detector (14(1) ... 14(x)) (pressure sensor, e.g. microphone) is arranged outside the measuring chamber, but is acoustically coupled to it. The narrow-band light source (13(1) ... 13(x)) has in this example an additional optical system, for example a collimating lens, as shown schematically in the figure. In this example, the medium to be measured is again sucked in from a reservoir via a pump.

12 shows an exemplary implementation of several light sources with additional sensors of the design of the 5 , in particular the miniaturization of the optical filter 11, the heating element 10 and the additional sensor 10a from 5 . The miniaturization can be done using semiconductor technology. All other elements of the 5 The values of the measuring channels shown remain unchanged.

In the realization of the 12 On one side of the wafer 15 there is an array of micro heaters (16(1) ... 16 (x)). Under the respective heater 16, for example, a MOX sensor, a thermal conductivity sensor or a heat tone sensor can be integrated as an additional sensor 17. These sensors 17(1) ... 17(x) can be of the same type. However, different sensor principles or heaters without an additional sensor can also be combined. On the other side of the wafer 15 there is an optical filter array with several filters (18(1) ... 18 (x); e.g. plasmonic filters). The heater 16 radiates broadband through the wafer 15 in the direction of the optical filters 18. The functional principle of the front side of this implementation has already been described in the EN 10 2021 108 745 A1 in connection with the 4 described in this patent publication. The additional sensors 17 on the back are new.

List of reference symbols

1

Light source

2

Detector unit

3

reservoir

4

Withdrawal system

5

Measuring chamber

6

pump

7

optical absorption detector

8th

PAS detector

9

Membrane, filter

10

IR heating element

10a

additional sensor

11

filter

12

Diffusion opening

13

Light source with optical system

14

PAS detector

15

Wafer

16

Micro heating element

17

additional sensor

18

filter

Ch

Measuring channel

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely to provide the reader with better information. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• EP 3508836 B1 [0003]
• DE 102021108745 A1 [0004, 0030]

Claims (16)

Arrangement for determining the concentration of one or more substances in a liquid or gaseous medium which have characteristic absorption peaks when illuminated with optical radiation, at least comprising - a measuring chamber (5) into which the liquid or gaseous medium can be introduced or through which the liquid or gaseous medium can flow, and - a number of measuring channels (Ch1, ... Chx), each of which is formed by a light source (1(1), ... 1(x)) and one or more detectors (7(1), ... 7(x), 8(1), ... 8(x)) assigned only to this light source, - wherein the number of measuring channels (Ch1, ... Chx) corresponds at least to the number of a selection from the characteristic absorption peaks which is at least required for determining the concentration of the one or more substances in the liquid or gaseous medium, and - wherein each measuring channel (Ch1, ... Chx) is designed such that it detects an absorption of optical radiation in the liquid or gaseous medium in the measuring chamber (5) for one of the characteristic Absorption peaks of the selection are measured by the light source (1(1), ... 1(x)) of this measuring channel emitting narrowband radiation that corresponds to a wavelength of the respective absorption peak. Arrangement according to Claim 1 , characterized in that the measuring channels (Ch1, ... Chx) each have an optical detector (7(1), ... 7(x)) and/or an acoustic detector (8(1), ... 8(x)) as a detector. Arrangement according to Claim 1 or 2 , characterized in that the measuring chamber (5) is connected to a pump (6) by which the liquid or gaseous medium can be conveyed through the measuring chamber (5). Arrangement according to one of the Claims 1 until 3 , characterized in that the measuring chamber (5) is tubular. Arrangement according to Claim 4 , characterized in that the measuring channels (Ch1, ... Chx) are arranged side by side along the measuring chamber (5). Arrangement according to one of the Claims 1 until 5 , characterized in that the light sources (1(1), ... 1(x)) are formed by narrow-band light emitters or by broadband light emitters with upstream narrow-band optical filter(s). Arrangement according to Claim 6 , characterized in that at least one of the broadband light emitters is a heating element (10) arranged outside the measuring chamber (5) which emits radiation in the IR range. Arrangement according to Claim 7 , characterized in that the measuring chamber (5) has at least one diffusion opening (12) in the region of the heating element (10), through which the liquid or gaseous medium can diffuse over the heating element (10), wherein the heating element (10) is simultaneously designed as a thermal conductivity detector. Arrangement according to Claim 7 , characterized in that an additional sensor (10a) is arranged on the heating element (10), in particular to realize a MOX sensor, a thermal conductivity sensor or a heat tone sensor, and the measuring chamber (5) in the region of the heating element (10) has at least one diffusion opening (12) through which the liquid or gaseous medium can diffuse via the additional sensor (10a). Arrangement according to one of the Claims 1 until 9 , characterized in that the measuring chamber (5) has a plurality of tubular projections which form separate measuring volumes, wherein a measuring channel (Ch1, ... Chx) is arranged on each of these projections. Arrangement according to Claim 10 , characterized in that the approaches are separated from the main volume of the measuring chamber (5) by a membrane or a filter (9(1) ... 9(x)) which allows only certain substances to diffuse into the approaches. Method for determining the concentration of one or more substances in a liquid or gaseous medium which exhibit characteristic absorption peaks when illuminated with optical radiation, using an arrangement according to one or more of the Claims 1 until 11 , in which - the liquid or gaseous medium is introduced into the measuring chamber (5) or is sucked or pumped through the measuring chamber (5), - on which a number of measuring channels (Ch1, ... Chx) is arranged which corresponds at least to the number of a selection from the characteristic absorption peaks which is at least required for determining the concentration of the one or more substances in the liquid or gaseous medium, - wherein each measuring channel (Ch1, ... Chx) is designed such that its light source (1(1), ... 1(x)) emits narrow-band radiation at a wavelength which corresponds to a wavelength of one of the absorption peaks corresponds to the selection, and - the absorption at the characteristic absorption peaks of the selection is measured with the measuring channels (Ch1, ... Chx). Procedure according to Claim 12 , characterized in that the measurement is carried out using the measuring principle of optical absorption spectroscopy and/or photoacoustic spectroscopy. Procedure according to Claim 12 or 13 , characterized in that the measurement with the individual measuring channels (Ch1, ... Chx) is carried out in chronological sequence. Method according to one of the Claims 12 until 14 characterized in that the radiation emitted by the light sources (1(1), ... 1(x)) of the measuring channels (Ch1, ... Chx) is modulated with different frequencies using the measuring principle of photoacoustic spectroscopy. Method according to one of the Claims 12 until 15 for determining the concentration of aroma components of a product, especially wine.

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