Assembly and method for determining the concentration of one or more substances in a liquid or gaseous medium
Patent Information
- Application Number
- EP2023798885
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-10-27
- Filing Date
- 2023-10-19
- Publication Date
- 2025-09-03
AI Technical Summary
Existing methods for determining the concentration of substances in liquid or gaseous media are limited in their ability to efficiently and cost-effectively analyze complex samples, particularly in the sub-ppb range, as they often require precise wavelength adjustment and are not adaptable to various substances with different absorption peaks.
The proposed arrangement features multiple measuring channels with narrow-band light sources and detectors, each optimized for specific characteristic absorption peaks, allowing for selective measurement of substances with minimal interference and cost-effective setup, using photoacoustic and absorption spectroscopy in combination.
This approach enables accurate and cost-effective determination of substance concentrations in complex samples by focusing on a selection of characteristic absorption peaks, enhancing sensitivity and adaptability for applications like wine aroma analysis and environmental monitoring.
Smart Images
Figure 1.1
Abstract
Description
[0001] Arrangement and procedure for determining the
[0002] Concentration of one or more substances in a liquid or gaseous medium
[0003] Technical application area
[0004] The present invention relates to an arrangement 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. The invention also relates to a method for determining the concentration using such an arrangement.
[0005] 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. This wave is recorded by a detector and converted into an electrical signal. A microphone, for example, can be used as a detector.The detected pressure change is a measure of the concentration of the corresponding substance. However, the measurements require an adjustment of the wavelength of the incident optical radiation to the substance(s) being measured. The required wavelength can be adjusted, for example, using a spectral filter or a tunable laser.
[0006] State of the art
[0007] For example, EP 3508836 B1 shows 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 adapted to the absorption maximum of the gas to be detected. By temporal modulation of the IR light source up to 100 Hz, the absorption of the radiation in the gas creates a sound wave within the measuring chamber. This sound wave 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.
[0008] DE 102021108745 A1 discloses an arrangement for multispectral light emission and a multispectral sensor equipped therewith, which enable simple and rapid adaptation or modification of the emitted wavelengths. This arrangement comprises a broadband light source in conjunction with a filter array comprising a plurality of 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 adaptation or variation of the wavelength or spectral distribution of the emitted optical radiation according to the number and characteristics of the different filters in the filter array.This allows the spectral distribution of the emitted light to be adapted to 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 comprises one or more broadband light sources, a filter array, a switching device, and a common detector.
[0009] Especially for the selective analysis of complex samples in the sub-ppb range, the concentration of many substances in a liquid or gaseous medium must be determined with high sensitivity. 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 that can be implemented cost-effectively and adapted to the respective application.
[0010] Description of the invention
[0011] This object is achieved by 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 derived from the following description and the exemplary embodiments.
[0012] 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, 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 which is at least necessary for determining the concentration of the one or more substances in the liquid or gaseous medium.This takes advantage of the fact that in many cases it is not necessary to measure all of the characteristic absorption peaks of a substance in order to clearly identify and determine the concentration, but rather it is sufficient to measure a smaller number of absorption peaks, i.e. a selection of the characteristic absorption peaks. Each measuring channel has at least one acoustic detector as the detector or one of the detectors and is designed such 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 such that it emits narrowband radiation at a wavelength which 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 measurement channel is designed to measure a different characteristic absorption peak of the selected sample.
[0013] In the present patent application, the light source is understood to be a light-emitting unit which emits narrowband 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 narrowband 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(s) then having the corresponding narrowband passband at the desired wavelength. Additional optical elements, for example lenses or optical fibers, can also be part of the light source.
[0014] The proposed design of the
[0015] This arrangement can be easily adapted to the respective measurement task, i.e., it can be specifically designed for the substances to be determined in the liquid or gaseous medium by selecting the required number and emission wavelength of the measurement channels. This modular principle and the independence of the individual measurement channels enable a cost-effective and simple setup. With this arrangement, even more complex samples can be measured cost-effectively, for example, in wine aroma analysis.
[0016] In the proposed arrangement, each measuring channel is designed for a specific wavelength. Either one acoustic detector for photoacoustic spectroscopy or several 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. In principle, in addition to the acoustic detectors, in particular pressure detectors or microphones, different types of detectors can be used in the measuring channels, for example microbolometers, pyroelectric detectors, resistive detectors (MOX), thermal conductivity detectors (TCD), catalytic detectors or photodetectors. Depending on the light source and detector, the detectors can also be integrated into the light source or the light emitter.This applies especially 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 transparent to the optical radiation, at least at the corresponding coupling or decoupling points.
[0017] 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 a plurality of tubular extensions along its longitudinal extent, 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 each arranged on these extensions, as is shown in more detail in a later exemplary embodiment.At the transition to these approaches, a membrane or filter can also be present, allowing only certain substances to diffuse into the approaches. This allows for a preliminary separation of the substances.
[0018] 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 which emits radiation in the IR range. In a particularly preferred embodiment, this radiant heater is simultaneously used as a thermal conductivity sensor in that its change in electrical resistance is recorded in the respective measuring channel. The measuring channel has a diffusion opening at the corresponding point in the region of this light emitter, through which diffusion opening a small part of the medium flowing through the measuring chamber is diffused out and guided over the light emitter. The diffusion opening can also be realized by an optical filter if this is designed accordingly, for example as a plasmonic filter. This means that CO2 or hydrogen, for example, can be detected using this light emitter.Alternatively, another sensor, such as an MOX sensor, a thermal conductivity sensor, or a thermal tone sensor, can be arranged near the light emitter designed as a heater. This sensor is then heated by the light emitter and therefore does not require its own heating element. In this case, the medium flows over this additional sensor, allowing CO2 or hydrogen, for example, to be detected.
[0019] The design described above, in which a heater is used as a light emitter and at the same time as a thermal conductivity sensor or in conjunction with an additional MOX sensor, thermal conductivity sensor or chromaticity sensor, can also be used independently of the existing arrangement as a measuring device which, for example, comprises only one light source or also an arrangement of several light sources or measuring channels which share a common detector.
[0020] In the proposed method, the proposed arrangement is designed in such a way that the number and light sources of the individual measuring channels are adapted to the selection of absorption peaks of the substances to be measured. 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 measure the absorption at the corresponding wavelength or the respective characteristic absorption peak in order to derive the concentration of the corresponding substances. 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.In another embodiment, the light sources of the individual measurement channels are modulated at different frequencies to generate acoustic waves with different frequencies that do not interfere with each other. This also prevents mutual interference between the individual measurement channels when they are operated simultaneously.
[0021] The proposed arrangement and the associated method can be used in many fields 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.
[0022] Short description of the drawings
[0023] The proposed arrangement and the associated method are explained in more detail below using exemplary embodiments in conjunction with the drawings. Herein:
[0024] Fig. 1 shows an example of characteristic absorption peaks of EtOH and ethyl acetate;
[0025] Fig. 2 shows an example of characteristic absorption peaks of CO and CO2;
[0026] Fig. 3 shows a first example of an embodiment of the proposed arrangement;
[0027] Fig. 4 shows an example of a special design of a measuring channel;
[0028] Fig. 5 shows a further example of a special design of a measuring channel;
[0029] Fig. 6 shows a further example of an embodiment of the proposed arrangement;
[0030] Fig. 7 shows a further example of an embodiment of the proposed arrangement; Fig. 8 shows a schematic representation of a time-shifted operation of the individual measuring channels in an embodiment of the proposed arrangement;
[0031] Fig. 9 is a schematic diagram of a control of different measuring channels with different frequencies;
[0032] Fig. 10 two further examples of the design of a measuring channel;
[0033] Fig. 11 shows a further exemplary embodiment of the proposed arrangement; and
[0034] Fig. 12 shows an exemplary implementation of the light sources and the further sensor in the embodiment of Figure 5.
[0035] Ways to implement the invention
[0036] The proposed arrangement takes advantage of the fact that individual substances in a liquid or gaseous medium have one or more characteristic optical absorption peaks (a so-called fingerprint) that can be used to clearly identify them and also to determine their concentration in a medium. Figure 1 shows an example of characteristic absorption peaks for EtOH (ethanol) and ethyl acetate. The left-hand part of the image shows the characteristic absorption peaks for ethanol, and the right-hand part shows the characteristic absorption peaks for ethyl acetate. To differentiate between these two substances, one measurement at three different wavelengths is sufficient: 3.4 pm, 8 pm, and 9.4 pm.With the proposed arrangement, the concentrations of these two substances in a liquid or gaseous medium can be determined using three measurement channels, each with a narrowband light source with a central wavelength of 3.4 pm, 8 pm, and 9.4 pm. The concentrations of the two substances can then be determined using the absorption intensity detected by the detector of the respective measurement channel and the ratio of this absorption intensity at the three wavelengths. The proposed arrangement and the associated method assume that the individual characteristic absorption peaks of the substances to be determined are known.
[0037] Figure 2 shows another example of characteristic absorption peaks of CO (carbon monoxide) and CO2 (carbon dioxide). As can be seen from the left-hand part of the figure, CO exhibits a characteristic absorption peak at a wavelength of 4.5 pm. The right-hand part of the figure shows that CO2 exhibits a characteristic absorption peak at a wavelength of 4.2 pm. Therefore, to differentiate between and determine the concentration of these two substances, measurements at two wavelengths (4.5 pm and 4.2 pm) are sufficient. For this purpose, the proposed arrangement accordingly has only two measurement channels for these two wavelengths.
[0038] Figure 3 shows an example of a possible design of the proposed arrangement. The measuring chamber 5 is tubular. The individual measuring channels (Chi, ... Chx) are arranged next to one another along the measuring chamber. In this example, each measuring channel (Chi, ... 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 narrowband light source (e.g. laser diode, LED) or a broadband light source with one or more upstream optical filters. The detector unit (2 (1) ... 2 (x)) can comprise one or more detectors. A PAS detector is used as the detector or one of the detectors.If there are multiple detectors per measuring channel, an additional optical absorption detector can also be used. The individual measuring channels (Chi, ... Chx) can be arranged next to one another in a modular manner. 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, depending on the measuring principle. During the measurement, the sample is sucked from a sample reservoir 3 through the measuring chamber by a pump 6 using a withdrawal system 4. While the sample flows through the measuring chamber 5, the measurement is carried out with the individual measuring channels.
[0039] The light sources (1 (1), ... 1 (x)) of the measuring channels (Chi, ... Chx) can be designed in different ways. Figure 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 that only transmits optical radiation at the corresponding wavelength. 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 via corresponding diffusion openings 12 on the measuring chamber 5 over the heating element 10 is enabled. By measuring the resistance on the heating element 10, the heating element can be used as a thermal conductivity detector, for example to detect CO2 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 positioned opposite the heating element 10 in the measuring chamber 5. Furthermore, a microphone 8 (1) is arranged within the measuring chamber 5 near the point where absorption occurs in order to perform a PAS measurement in addition to the optical absorption measurement.
[0040] Figure 5 shows an alternative embodiment to Figure 4, in which the heating element 10 is not used as an additional detector, but rather a further sensor 10a next to or below the heating element 10. This additional sensor 10a can be, for example, an MOX sensor, a thermal conductivity sensor, or a chromatic emission sensor (each without its own heating element), which is heated by the heating element 10 used as an IR emitter. In this example, the medium exiting through the diffusion opening 12 thus flows over this additional sensor 10a to detect, for example, CO2 or hydrogen.
[0041] Figure 6 shows a further exemplary embodiment of the proposed arrangement, in which the measuring chamber is again tubular and the individual measuring channels (Chi, ... 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 (Chi, ... Chx) each have a corresponding light source, an opposite optical absorption detector (7 (1), ... 7 (x)), and a microphone (8 (1), ... 8 (x)) as a PAS detector, and are arranged along the horizontally arranged measuring chamber.
[0042] The measuring chamber itself can also have tubular extensions specially designed for the measurement, as shown in the example in Figure 7. These extensions 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 extensions 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 extension in order to increase the selectivity of the measurement. Such a membrane or filter can also be used at the diffusion openings 12 of the embodiments in Figures 4 and 5.The membrane or filter can then be used for pre-separation in the gas phase – in the case of a gaseous medium – or to measure gas dissolved in the liquid – in the case of a liquid medium. The individual measuring channels each have a light source and one or more detectors, as already evident from the previous embodiments.
[0043] If multiple measurement channels are used, as in the proposed arrangement with a PAS detector, and the light in the individual measurement channels is modulated with the same frequency f(l), there is a risk of mutual interference between the individual channels, as the generated acoustic waves may interfere with each other. In one embodiment of the proposed method, the individual measurement channels are therefore operated sequentially, so that at a given time (t(l), ... t(x)), only one measurement channel is active at a time, i.e., only one light source is switched on at a time. This is shown schematically in Figure 8. The individual measurement channels can be operated in any order.
[0044] Alternatively, the light sources of the individual measuring channels can also be modulated with different frequencies (f (l), ... f (n)). This enables the simultaneous operation of all measuring channels; thus, all measuring channels are active at any one time, since resulting acoustic waves with different frequencies do not interfere with one another. This is shown schematically in Figure 9 for two measuring channels Chi, Ch2, which in the right-hand part of the figure schematically shows the modulation signals for the light sources of the two channels Chi, Ch2. The acoustic waves induced in this way do not interfere with one another because they are modulated differently. With additional electronics, the interfering signal from 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 in Figure 8.
[0045] If photodetectors are also used, i.e. if the optical absorption of the light emitted by the light source is measured directly, measurements can be taken both in reflection and in transmission. This is shown in the two partial images in Figure 10 for the different embodiments already described above. In this example, each measuring channel additionally has two photodetectors 7 for a light source 1. Only the absorption detector on the opposite side requires direct irradiation and must therefore 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 measuring volume, as shown schematically in the two partial images.
[0046] Finally, Figure 11 shows another 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 narrowband light source ( 13 ( 1 ) ... 13 (x ) ) in this example additionally has an optical system, e.g. a collimating lens, as is schematically indicated in the figure. In this example too, the medium to be measured is sucked in from a reservoir via a pump.
[0047] Figure 12 shows an exemplary implementation of multiple light sources with additional sensors of the configuration shown in Figure 5, in particular the miniaturization of the optical filter 11, the heating element 10, and the additional sensor 10a from Figure 5. The miniaturization can be achieved using semiconductor technology. All other elements of the measuring channel shown in Figure 5 remain unchanged.
[0048] In the implementation shown in Figure 12, an array of microheaters (16(1) ... 16(x)) is located on one side of the wafer 15. For example, an MOX sensor, a thermal conductivity sensor, or a chromatic emission sensor can be integrated as an additional sensor 17 beneath the respective heater 16. 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 DE 10 2021 108 745 A1 in conjunction with Figure 4 of this patent publication. New are the additional sensors 17 on the rear. Reference symbols
[0049] 1 light source
[0050] 2 detector unit
[0051] 3 Reservoir
[0052] 4 Withdrawal system
[0053] 5 Measuring chamber
[0054] 6 Pump
[0055] 7 optical absorption detector
[0056] 8 PAS detector
[0057] 9 Membrane, filter
[0058] 10 IR heating element
[0059] 10a additional sensor
[0060] 11 filters
[0061] 12 Di f fusion opening
[0062] 13 Light source with optical system
[0063] 14 PAS detector
[0064] 15 wafers
[0065] 16 Micro heating element
[0066] 17 additional sensors
[0067] 18 filters
[0068] Ch measuring channel
Claims
Patent claims 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 consisting of - 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 (Chi, ... Chx), each 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 (Chi, ... Chx) corresponds at least to the number of a selection from the characteristic absorption peaks which is at least necessary for determining the concentration of the one or more substances in the liquid or gaseous medium, - wherein the measuring channels (Chi, ... Chx) each have at least one acoustic detector (8 (1), ... 8 (x)) as detector(s), and - wherein each measuring channel (Chi, ... Chx) is designed to measure 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 by the light source (1 (1), ... 1 (x)) of this measuring channel Narrowband radiation is emitted that corresponds to a wavelength of the respective absorption peak. Arrangement according to claim 1, characterized in that the measuring channels (Chi, ... Chx) each also have at least one optical detector (7 (1), ... 7 (x)) as detectors. 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 claims 1 to 3, characterized in that the measuring chamber (5) is tubular. Arrangement according to claim 4, characterized in that the measuring channels (Chi, ... Chx) are arranged side by side along the measuring chamber (5). Arrangement according to one of claims 1 to 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 filters (n). 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 via 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 implement an MOX sensor, a thermal conductivity sensor, or a chromaticity sensor, and 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 via the additional sensor (10a).Arrangement according to one of claims 1 to 9, characterized in that the measuring chamber (5) has a plurality of tubular projections which form separate measuring volumes, with a. Measuring channel (Chi, ... Chx) is arranged. Arrangement according to claim 10, characterized in that the attachments are separated from the main volume of the measuring chamber (5) by a membrane or a filter (9(1) ... (x)) which allows only certain substances to diffuse into the attachments. 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, with an arrangement according to one or more of claims 1 to 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 (Chi, ... Chx) is arranged which corresponds at least to the number of a selection of the characteristic absorption peaks which is at least necessary for determining the concentration of the one or more substances in the liquid or gaseous medium, - wherein each measuring channel (Chi, ... Chx) is designed such that its light source (1 (1), ... 1 (x)) emits narrow-band radiation at a wavelength corresponding to a wavelength of one of the absorption peaks of the selection, and - with the measuring channels (Chi, ... Chx) the absorption at the characteristic Absorption peaks of the selection are measured. Method according to claim 12, characterized in that the measurement is carried out using the measuring principle of photoacoustic spectroscopy. Method according to claim 13, characterized in that the measuring principle of optical absorption spectroscopy is additionally used for the measurement. Method according to one of claims 12 to 14, characterized in that the measurement is carried out with the individual measuring channels (Chi, ... Chx) in chronological sequence. Method according to one of claims 12 to 15, characterized in that the radiation emitted by the light sources (1 (1), ... 1 (x)) of the measuring channels (Chi, ... Chx) is modulated with different frequencies when using the measuring principle of photoacoustic spectroscopy. Method according to one of claims 12 to 16 for determining the concentration of aroma components of a product, in particular of wine.