DEVICE AND METHOD FOR VARIABLE PRESSURE-DEPENDENT ENRICHEMENT AND SPECTROSCOPIC DETERMINATION OF AN ANALYTE IN A GAS OR VAPOR SAMPLE

Description

[0001] The invention relates to a device and a method for the spectroscopic measurement of analytes in a gaseous or vaporous sample. The invention further relates to a device and a method for the qualitative and quantitative spectroscopic determination of substances present in a gaseous or vaporous phase, for example, pollutants, which often occur in minute quantities and therefore place high demands on the sensitivity of the optical measuring devices. The invention particularly relates to a corresponding device and a method with which the measurement-specific sensitivity of the device can be varied by defined, predetermined, pressure-dependent enrichment of an analyte in a gaseous or vaporous sample and thus adapted to the properties of the analyte to be measured. This also makes analyses of, for example, hydrogen, CO₂ (containing <14C), or explosives and chemical warfare agents possible.

[0002] Spectroscopy is a proven and rapid method for the qualitative and quantitative analysis of many elements and compounds in aqueous, gaseous, or solid phases. It is mostly based on the attenuation of radiation through interaction with atoms and / or molecules. Optical analysis methods are increasingly replacing conventional chemical analysis of gases. They utilize the effect that atoms and molecules absorb light at specific wavelengths and have the advantage of rapid results. The detection of gases and the determination of their concentrations are possible in situ, without the need for sample extraction. Such methods are therefore generally well-suited for transient chemical processes or rapidly flowing gases.

[0003] The measuring instruments used for this purpose essentially consist of a light source, an open or closed cuvette through which the fluid to be measured flows, a system of analyzer and detector for spectral analysis of the incident light, and a device for data acquisition and transmission.

[0004] Methods and devices for determining gaseous analytes are known in the prior art.

[0005] WO 2001 / 27596 A1 describes a carbon monoxide sensor for the spectroscopic determination of carbon monoxide / carbon dioxide as a component of reformed gases in

[0006] The gas composition is determined by applying pressure to a measuring cell and varying the pressure within the cell. This system allows for the qualitative and quantitative determination of gases with high accuracy.

[0007] US Patent 2003 / 0098419 A1 describes a device and method for the qualitative and quantitative spectroscopic determination of halogen gases. It states that high accuracy and sensitivity of the measurement can be achieved by varying the pressure of the gas sample in the measuring cell or by changing the optical path length of the measuring cell.

[0008] US Patent 2003 / 0015019 A1 discloses, among other things, a spectroscopic method for analyzing gases, in particular using "pneumatic focusing." This means that the gas sample is compressed to a smaller volume in the measuring cell before measurement in order to achieve an enhanced signal and higher sensitivity. Further relevant devices for the spectroscopic analysis of a gaseous or vaporous sample under increased pressure in the sample measuring chamber are disclosed in DE 20 2022 000633 U1, WO 01 / 27596 A1, and US Patent 2011 / 147592 A1.

[0009] The underlying spectroscopic methods of the state of the art all utilize a physical phenomenon that can be expressed, for example, by the Lambert-Beer law, which is described below.

[0010] Broadband emitters are often used as light sources for measuring molecules, or line emitters with a narrowband emission line resonant with the analyte.

[0011] The absorption of light when passing through a sample depends mainly on the composition / structure of the sample and the frequency of the light (wavelength).

[0012] The intensity of the light passing through the sample changes proportionally to the absorption coefficient and the optical path length (sample layer thickness). A monochromatic light source with intensity I0 passes through a dilute solution of a specific chemical substance with layer thickness d, resulting in an intensity I1. E λ = log 10 I 0 I 1 = ε λ ⋅ c ⋅ d . or I 1 = I 0 xe -ε(xcxd)< where: I₀: Intensity of the incident light beam; I₁: Intensity of the transmitted light beam through the layer thickness; dd: Layer thickness d, or optical path length (cm); c: Concentration of the absorbing substance : Molar extinction coefficient at specific wavelength for this substance : Extinction at a specific wavelength e : Euler's number (approximately 2.72)

[0013] The extinction coefficient ε is an inherent material constant whose numerical value can vary over many orders of magnitude depending on the material. The concentration c to be measured depends on the specific analytical question and can also vary over many orders of magnitude. Ideally, under controlled measurement conditions (e.g., temperature, solvent, pH), ε depends only on the type of absorbing substance and the wavelength λ.

[0014] If the optical path length d and the chemical substance are known (i.e., ε), the unknown concentration c of a substance can be determined by measuring the absorbance E at a specific wavelength. It follows that, for a given concentration c of a specific analyte, the sensitivity of the measurement for a given detector system ideally depends solely on the optical path length of the irradiated sample, typically the path length (OPL) of the measuring cuvette. Therefore, the sensitivity for a specific substance in a measuring device with the same detector system can only be increased by increasing the optical path length, or the cuvette length d. Corresponding cuvettes of any length and made of any material, equipped with appropriately prefabricated and easily attachable cuvette end pieces, are known in the prior art.These cuvette end pieces in the form of standard ground glass cores are equipped with integrated input and output coupling optics and fiber optic connections or light sources and detectors, so that the cuvette length can be easily adapted to the measuring system or the analyte to be measured (DE 20 2012 003 739 U1).

[0015] However, changing the optical path or cuvette length is not always possible or advantageous, particularly when, for example, the necessary long cuvette length for evaluable absorbances at low analyte concentrations is not feasible due to space constraints or other technical reasons. Conversely, with certain analytes in specific concentration ranges and certain detector systems, it may be necessary to significantly shorten the optical path length to obtain usable measurement results. In this case, too, there may be technical limitations to any reduction in cuvette length.

[0016] The object of the present invention was therefore to provide a spectroscopic device and a spectroscopic method for the quantitative and / or qualitative measurement of analytes in a gaseous or vaporous sample using a device which is not only available at a defined cuvette length in a

[0017] The aim is not only to demonstrate that the sensitivity or absorbance of a given optical measuring system can be increased, and thus the detection limit lowered, by means of, for example, higher pressure or volume reduction under pressure in a measuring cell, but also to propose measures that go beyond the known physical relationships of the affected parameters and lead to a further increase in sensitivity or a reduction of the detection or quantification limit of the measuring system. Other important boundary conditions should also be considered, namely volume minimization, length minimization of the measuring cell, weight optimization, a simple, insensitive optical arrangement, the supply of the sample containing the analyte from the environment or industrial processes of any kind, and the adjustment of the sensitivity to the operating range of the selected analytical system.

[0018] The problems were solved by the device according to the invention, as described in the claims and below.

[0019] It was found that the sensitivity of spectroscopic measurement and the detection / quantification limit of an analyte in a gaseous or vaporous process environment can be increased if the analyte to be determined is first compressed from the process that produces it by a compressor device before being transferred to the measuring cell, thereby enriching it or significantly increasing its concentration, and then subsequently or during this process transferred to the measuring cell at a pressure that can be regulated via the compressor device and analyzed there spectroscopically in a qualitative and quantitative manner.

[0020] The invention relates to an analytical device operable with variable sensitivity for the spectroscopic determination of the chemical, physical, or physicochemical properties of an analyte from a gaseous or vaporous sample taken from a defined process environment. The device according to the invention is defined in claim 1 and essentially comprises: a light source, a pressure-stable sample measuring chamber (e.g., cuvette) for holding the sample containing the analyte, which is illuminated by the light of the light source and has adjustable inlet and outlet openings for supplying the sample containing the analyte and for variable pressurization and pressure relief of the sample measuring chamber, a detector system equipped with input and / or output coupling optics or with other adjustable optical or optoelectronic means, which is capable of spectrometric analysis of the light transmitted, reflected, or emitted in the sample measuring chamber, as well as devices for automatic acquisition and evaluation of the measurement data, wherein according to the invention the analysis device is equipped with a compressor device which is connected to an inlet opening of the sample measuring chamber in such a way that the gaseous or vaporous sample with the contained analyte is drawn in from the process environment on the inlet side and thereby enriched in the compressor and transferred on the outlet side to the sample measuring chamber at a preset selectable pressure or compressed within the measuring chamber, thereby simultaneously achieving a corresponding variable enrichment of the analyte in the sample measuring chamber adapted to the selected or available working range.

[0021] In contrast to the aforementioned prior art documents, the pressure increase of the sample to be analyzed does not occur in or immediately before its introduction into the measuring cuvette, but rather in a separate device using a compressor, at any point before the transfer to the actual sample measuring chamber. This results not only in a pressure-compressed sample, which, as described in the prior art, already initiates a lower detection limit and thus higher sensitivity for physical reasons (Lambert-Beer), but also, and crucially, in a significant and technically very controllable enrichment of the quantity or concentration of the gaseous sample to be determined, and thus of the analyte. This enrichment can then be controlled and transferred from the separate compressor device to the sample measuring chamber in a more concentrated form than before.This significantly lowers the detection and quantification limits for the analyte without requiring any optimization or modification of the spectroscopic measurement method.

[0022] According to the invention, the compressor device comprises at least one collection or storage container which, on the input side, receives and temporarily stores a gaseous or vaporous sample containing the analyte to be determined directly from the process environment generating it via at least one first adjustable feed, and on the output side, feeds the compressor device with the temporarily stored sample containing the analyte via at least one second adjustable feed.

[0023] From the compressor device, the gaseous or vaporous sample, pressurized and containing the simultaneously enriched analyte, can now be transferred in a targeted and controllable manner into the sample measuring chamber via mechanical or electronic valves and analyzed spectroscopically.

[0024] This device thus makes it possible to easily determine the working range of the analyte to be determined in relation to the selected measuring system and the existing measuring conditions by targeted pressure changes.

[0025] The invention therefore also relates to a method for increasing the sensitivity of a spectroscopic measurement according to claim 8.

[0026] A method for the spectroscopic qualitative and / or quantitative determination of an analyte in a gaseous or vaporous sample for a defined spectroscopic measuring system using this device is also described, whereby the concentration of the enriched sample and thus of the enriched analyte in the sample measuring chamber is changed by targeted pressure changes via the compressor device until the detection or quantification limit of the analyte is reached and the analyte can thus be determined.

[0027] By finding the maximum upper and lower concentrations of the analyte, the working range of the spectroscopic measurement for this analyte for the selected measuring system and under the selected measuring conditions can be determined by simply changing the pressure above or through the compressor device.

[0028] With the aid of the device according to the invention, the spectroscopic determination of an analyte can also be very easily subjected to calibration with respect to a given measuring system.

[0029] Therefore, the use of the device according to the invention described here for calibrating a spectroscopic measurement of the concentration of an analyte to be determined in a gaseous or vaporous sample in a selected measurement environment is also described, taking into account in particular pressure, temperature, length of the sample measurement chamber and type of analyte, by considering the possible

[0030] The working range of the measuring system is determined by changes in the concentration of the sample or analyte in the sample measuring chamber by means of targeted pressure changes via the compressor device.

[0031] According to the invention, the term "analyte" refers to a substance to be determined that is present (or optionally absent) in a gaseous or vaporous sample and is typically found in the sample alongside other substances not intended for measurement (matrix). This substance can be an atom, a molecule, or a more complex chemical compound in gaseous or particulate form.

[0032] According to the invention, the term "limit of quantification" refers to the lowest concentration of an analyte that can be quantitatively determined with a defined precision. Quantitative analytical results are only reported above the limit of quantification. The limit of quantification always has a higher accuracy than the limit of detection.

[0033] According to the invention, the term "detection limit" refers to the extreme value of a measurement method up to which the measured quantity can still be reliably detected.

[0034] According to the invention, the term "working range" is understood to be the range between the lower and upper concentration of a quality assurance analysis, in which the measurement error is still within the acceptable range.

[0035] According to the invention, the term "process environment" refers to the conditions under which the sample and the analyte to be determined are formed, processed, and / or analyzed. These conditions can be not only physical in nature but can also include, for example, environmental influences (e.g., pollution).

[0036] Using a compressor device according to the invention with an upstream storage tank, the following possibilities are therefore available: Pressure increase, pressure reduction (if necessary), pressure control, flow control. Supply of the sample with the analyte via an intermediate container allows independence from process conditions (e.g., process has 0.6 MPa (6 bar), measuring cell 5 MPa (50 bar), or vice versa, process has 8 MPa (80 bar), the operating range is optimal at 3 MPa (30 bar)). Enrichment: Adjustment of the sensitivity to the operating range of the analysis system via the preselected pressure.

[0037] As already mentioned, the device according to the invention offers an elegant and simple way of calibrating a measuring system as a function of a multidimensional characteristic map, for example, comprising parameters such as temperature, pressure, the linear expansion of the sample measuring chamber, and the concentration of the analyte. For calibration-dependent measurement techniques, knowledge of the variable parameters, such as pressure, temperature, and concentration, is essential for the measurement. In particular, when using a compressor device according to the invention, the ratio of pressure to concentration concentration plays a crucial role.

[0038] The method, in its spectroscopy-based version, therefore offers the possibility of finding an optimal setting for a selected analyte within a defined configuration of the measuring system (system setup consisting of light source, detector, OPL measuring cell, etc.) by adjusting the runtime and power of the compressor and the pressure generated thereby, which makes it possible to to determine and set the detection and quantification limit by adjusting the pressure, and to adapt and optimize the working range of the intended measuring system to the preselected pressure, wherein The pressure is set so that the working area is within the range of validity of Lambert Beer's law or can be linearized using simple methods.

[0039] After determining and subsequently defining the relevant parameters, operations can then be carried out within this optimized workspace.

[0040] Further metrologically relevant coordinates arise when the analyte or parts of the matrix are capable of undergoing chemical reactions, such as carbon dioxide and water reacting to form carbonic acid, or of condensing under certain conditions. To account for these latter possible effects and events metrologically, most known methods often require a separation process, such as gas chromatography, prior to the actual analysis. The method according to the invention allows such complex pretreatments to be avoided to a greater extent than with conventional techniques.

[0041] Furthermore, solvatochromic effects must be taken into account, as they arise from both the composition of a sample and from simple variables. It is generally known that the pressure within a sample influences (e.g., Lorenz broadening) the spectral absorption and emission behavior of the particles contained in the sample, which normally has to be considered, among other things, during the calibration of the measuring instrument used. Solvatochromic effects are currently not precisely predictable in science, neither for the coordinates of composition nor for the influence of pressure. In addition, there is the change in concentration due to enrichment. Therefore, the calibration model must be completely determined for each individual application.

[0042] This invention makes it possible to use these effects to change sensitivity.

[0043] Of course, it remains possible to significantly shorten the optical path length and thus the cuvette length while maintaining constant sensitivity. The device according to the invention preferably has a light source with a wavelength range of preferably 180–2700 nm. The light source can include optical fibers and corresponding optics. In one embodiment of the invention, the optical fiber connections can be replaced by suitable integrated light sources or, conversely, by integrated detectors. Absorption or emission spectrometers for visible light, or for IR, UV, or X-ray radiation, or Raman spectrometers can be used as the detector system.

[0044] The optics used can include input and / or output coupling optics or other optical or optoelectronic means for optimizing and controlling the light traversing the sample chamber. Such optical means are known in the prior art. The device according to the invention can be used for qualitative and quantitative analyses by means of system calibration, using defined standards (e.g., optical filters or turbidity standards), or by means of reference samples with known properties.

[0045] The measuring fluid is guided through suitable, adjustable process connections, which are preferably located at opposite ends of the pressure-stable measuring chamber. For this purpose, a device for the preferably automatic provision of the analyte and / or for increasing the analyte concentration in the sample to be measured is expediently provided. According to the invention, the process connections, or the device for providing the gaseous analyte, are connected to a pressure-generating device, for example, a compressor or a pneumatic cylinder as commonly used in the prior art.

[0046] The sample measuring chamber of the device according to the invention is preferably a thin tube or a capillary, preferably made of steel or another suitably pressure-resistant material, generally of any length, for example from 5 to 2000 cm, preferably 10 to 300 cm. The tubes, as well as the optical and other connections, should be designed to withstand pressures > 1 MPa (10 bar), preferably > 2 MPa (20 bar), or even > 20 MPa (200 bar). Several tubes can also be connected in series in a pressure-tight manner, for example, to perform several measurement tasks simultaneously.

[0047] It is advantageous to use thin tubes or capillaries with prefabricated end pieces as sample measuring chambers. In their simplest design, these end pieces consist of a cone containing a fiber optic coupling and input / output optics. For example, two such cones—one with a fiber optic connection and input optics, and the other with a fiber optic connection and output optics—can be connected to the front and rear sleeves of a tube of a length suitable for the measurement task. Fiber optic connections can then be coupled to a light source or, on the opposite side, to a detector (e.g., a spectrometer) in a known manner. Preferably, the cones have standard ground glass joint dimensions (e.g., NS 29 / 32) with corresponding standard ground glass joints, so that, if necessary, several pressure-resistant tubes can be inserted one after the other and clamped pressure-tight to complete the measuring system.

[0048] FIG. 1 Figure 1 schematically shows the structure of an embodiment of the device according to the invention, including a compressor unit for enriching a gaseous sample or an analyte contained therein and its spectroscopic determination. The compressor unit comprises the actual compressor and a storage container connected to it.

[0049] Outside the scope of the present invention, a gaseous sample containing the analyte (1) is drawn from a process environment (e.g., room air, breathing air, industrial gases, exhaust gases, other gases) into a compressor (3) or drawn in by it (arrow b). According to the invention, the sample containing the analyte to be determined is fed into an upstream storage container (2) and collected there (arrow a) until a sufficient quantity is available for compression. From the compressor device, the sample thus enriched, or the analyte thus enriched, is directed via an inlet valve (4) into a tubular sample measuring chamber (5) of defined optical length, preferably made of steel, which is equipped with optical connections (input and output coupling optics 7, 8), a light source (9), and a detector (10). The optical paths are indicated by narrow arrows. Furthermore, a control and evaluation unit (11) is provided, e.g.,a computer equipped with control and management software and data lines.

[0050] Fig. 2 (a) shows the absorption of acetone in a gaseous sample under normal pressure in a wavelength range of approximately 250 nm to 600 nm without the use of the device according to the invention.

[0051] In contrast, using the device according to the invention, as described, acetone-containing gas is drawn from a storage container and fed into a measuring cell / sample measuring chamber at a pressure of 3 bar (b) and 5 bar (c).

[0052] This demonstrates how the signal for acetone changes over time and at the set pressure as the pressure increases with concentration. At P = 0.3 MPa (3 bar), acetone is already clearly detectable and could be reliably evaluated by expressing its peak. At P = 0.5 MPa (5 bar), acetone is very pronounced and easily evaluable, and this within an optimal (proportional) range.

[0053] Spectra (a), (b) and (c) show how the optimal sensitivity range can be set by adjusting the pressure. It is self-evident that the pressure setting must be precise, and preferably a pressure-dependent calibration should be performed in the defined measuring system.

[0054] The increased sensitivity achieved through pressure increase and enrichment, which can be achieved according to the invention using a compressor, is demonstrated by comparison with the results from US 2003 / 0015019 A1 cited above, which concerns the measurement of acetone in ambient air in a UV / VIS measuring cell (see in particular Figures 45, 46 and 49 therein). In this prior art experiment, a compressor is indeed used, but only to increase the pressure by simply displacing the existing gas and not for targeted enrichment, as is possible with the device and method described here according to the invention.

[0055] The difference is significant: According to the aforementioned US application, a pressure increase of 500 psi (equivalent to 3.437 MPa or 34.37 bar) is required to double a signal of sufficient quality (Fig. 46). In contrast, the system described here according to the invention requires only a pressure increase of 2 bar, from 3 to 5 bar, to obtain a similarly good signal. The path length (OPL) in the measuring cell only secondarily influences the signal quality. The lower detection limit is primarily determined by the selected pressure and the associated enrichment of the analyte in the sample by means of a compressor. This means that a similarly good signal compared to the prior art is achieved at approximately one-tenth of the pressure (comparison between FIG. 46 of US 2003 / 0015019 A1 and Fig 2 this invention).

[0056] Regarding sensitivity, US patent 2003 / 0015019 A1 describes that increasing the pressure by a further 500 psi (corresponding to 3.437 MPa or 34.37 bar) results in a doubling of the intensity, whereas this is achieved with the described method according to the invention with a pressure increase of less than 2 bar. In comparison, the increase in sensitivity and thus also the achievable lower detection limit of the method according to the invention should therefore be emphasized.

[0057] The example of "acetone" shows that a significant increase in sensitivity can be achieved by increasing the pressure, including enrichment via a compressor according to the invention.

Claims

1. Device operable with variable sensitivity for spectroscopically determining the chemical, physical or physicochemical properties of an analyte as a component of a gaseous or vaporous sample taken from a predetermined process environment, comprising: - a light source (9), - a pressure-stable sample-measuring chamber (5) for receiving the sample containing at least one analyte to be determined, which sample is irradiated with the light from the light source (9), - a detector system (10) which is equipped with input and / or output coupling optics or with other adjustable optical or optoelectronic means (7, 8), and is capable of spectrometrically analyzing the light transmitted, reflected or emitted in the sample-measuring chamber (5), and - devices for automatically capturing and evaluating the measurement data (11), and - a compressor device connected to an inlet opening of the sample-measuring chamber (5), the sample-measuring chamber (5) having adjustable inlet and outlet openings for supplying the sample containing the analyte and for variable pressurization and pressure relief of the sample-measuring chamber (5), characterized in that the compressor device comprises a compressor (3) and at least one collection or storage container (2), which, on the inlet side, receives a sample of the gaseous or vaporous analyte directly from the process environment (1) via a first adjustable feed and temporarily stores said sample, and, on the outlet side, supplies the compressor (3) with the temporarily stored sample containing the analyte to be determined via a second adjustable feed, the compressor (3) being provided for enriching the gaseous or vaporous sample containing the analyte, which is drawn from the collection or storage container (2), under compression with a preset selectable pressure and, after enrichment has taken place, for transferring the sample via mechanical or electronic valves in a targeted and adjustable manner into the sample-measuring chamber (5), whereby a corresponding variable increase in concentration of the analyte in the sample-measuring chamber (5) is simultaneously achieved, which increase is adapted to the selected or available working range.

2. Device according to claim 1, characterized in that the sample-measuring chamber (5) is designed in the form of a tubular measuring cell which is suitable for pressures from 10 kPa to at least 200 MPa.

3. Device according to claim 2, characterized in that the sample-measuring chamber (5) has a defined length of 3 to 300 cm.

4. Device according to any of claims 1 - 3, characterized in that the light source (9) and detector system (10) are equipped with optical waveguides (7, 8).

5. Device according to any of claims 1 - 4, characterized in that light having a wavelength range of 160 - 35000 nm is provided as a broadband light source (9).

6. Device according to any of claims 1 - 5, characterized in that a Raman spectrometer, a fluorescence spectrometer or an absorption or emission spectrometer for visible light, or for IR, UV or X-ray radiation, is provided as the detector system (10).

7. Device according to any of claims 1 - 6, characterized in that the gaseous or vaporous sample containing the analyte to be determined is a portion of a protective gas or of air.

8. Method for increasing the sensitivity of a spectroscopic measurement and thus lowering the detection and determination limit of an analyte in a gaseous or vaporous sample by means of a device; which comprises - a light source (9), - a pressure-stable sample-measuring chamber (5), provided with adjustable inlet and outlet openings, for receiving the sample which is irradiated with the light from the light source (9), - a detector system (10) which is equipped with input and / or output coupling optics or with other adjustable optical or optoelectronic means (7, 8), and is capable of spectrometrically analyzing the light transmitted, reflected or emitted in the sample-measuring chamber (5), - devices for automatically capturing and evaluating the measurement data (11), and - a compressor device connected to an inlet opening of the sample-measuring chamber (5), characterized in that the compressor device comprises a compressor (3) and at least one collection or storage container (3), and in that the sample of the gaseous or vaporous analyte from a process environment (1) is introduced into the collection or storage container (2) and enriched under compression by means of the compressor (3) with a preset selectable pressure, and, after enrichment, is transferred via mechanical or electronic valves in a targeted, adjustable manner and in a concentrated form into the sample-measuring chamber (5) and analyzed spectroscopically.

9. Method according to claim 8, characterized in that the concentration of the enriched sample is changed by a targeted pressure change by means of the compressor device (3), before transfer into the sample-measuring chamber (5), until the detection or determination limit of the analyte is reached and the analyte can thus be determined.

10. Method according to claim 9, characterized in that the working range of the spectroscopic measurement for the analytes in the sample and for the selected measuring system and the selected measuring conditions is determined by finding the maximum upper and lower concentration of the analyte.

11. Method according to any of claims 8 - 10, characterized in that a sample-measuring chamber (5) is used, which is designed in the form of a tubular measuring cell having a defined length of 3 to 300 cm and is suitable for pressures from 10 kPa to at least 200 MPa.

12. Method according to any of claims 8 - 11, characterized in that a light source (9) and a detector system (10) having optical waveguides (7, 8) are used.

13. Method according to any of claims 8 - 12, characterized in that light having a wavelength range of 160 - 35000 nm is used as a broadband light source (9).

14. Method according to any of claims 8 - 13, characterized in that a Raman spectrometer, a fluorescence spectrometer or an absorption or emission spectrometer for visible light, or for IR, UV or X-ray radiation, is used as the detector system (10).

15. Method according to any of claims 8 - 14, characterized in that the gaseous or vaporous sample containing the analyte to be determined is a portion of a protective gas or of air.