Method for determining the concentration of at least one target analyte in a liquid using a measurement signal in a gaseous sample composition, use of an adaptation function, and gas detection device for carrying out the method

Abstract

The invention relates to a method (500) for determining the concentration of at least one target analyte (ZA) in a liquid (52), said liquid (52) containing at least one other chemical compound (CV). The method has the steps of: drawing (S501) a gaseous sample composition (gP) from a region located in the vicinity of the liquid (52), in particular above the liquid; determining (S502) a quantitative measurement signal of the target analyte (ZA) in the gaseous sample composition (gP); determining (S503) or inputting at least one other characteristic value of the at least one other chemical compound (CV) of the liquid (52); and converting (S504) the measurement signal of the target analyte (ZA) determined in the gaseous sample composition (gP) into a concentration of the target analyte (ZA) in the liquid (52) using an adaptation function (AF), wherein the measurement signal of the target analyte (ZA) and the at least one characteristic value of the at least one other chemical compound (CV) of the liquid (52) are used as input parameters for the adaptation function (AF).

Description

[0001] Method for determining the concentration of at least one target analyte in a liquid by means of a measurement signal in a gaseous sample composition and use of an adaptation function and gas detection device for carrying out the method

[0002] DESCRIPTION:

[0003] The invention relates to a method for determining the concentration of at least one target analyte in a liquid, wherein the liquid contains at least one further chemical compound, comprising the steps of: taking a gaseous sample composition from a region located in the vicinity of, in particular above, the liquid; determining a quantitative measurement signal of the target analyte in the gaseous sample composition; converting the measurement signal of the target analyte determined in the gaseous sample composition into a concentration of the target analyte in the liquid by means of an adjustment function, wherein the measurement signal of the target analyte and the at least one characteristic value of the at least one further chemical compound of the liquid are used as input parameters for the adjustment function.

[0004] Analysis in an area close to, particularly above, a liquid, especially in the headspace of a container, also known as headspace analysis, is a well-known procedure in analytical chemistry. This involves quantifying the concentration of one or more target analytes, particularly in the saturated headspace above the sample liquid. The sample liquid itself, which can also be referred to as the sample matrix, can be a single component (e.g. water) or a mixture of several components (e.g. water with ethanol, water with ethanol and methanol, water and salt, water and sugar, or the like). The concentration of target analytes and other chemical compounds, which can also be referred to as matrix components, in the gas phase is proportional to the concentration in the liquid and is described by a partition coefficient.The partition coefficient of a particular compound depends on the composition and concentration of the liquid. For some simple sample liquids (sample matrix), such as water, the partition coefficients for a variety of analytes are known and can be obtained from the corresponding tables.

[0005] See, for example, Sander, R.: Compilation of Henry's law constants (version 5.0.0) for water as solvent, Atmos. Chem. Phys., 23, 10901-12440, https: / / doi.org / 10.5194 / acp-23-10901-2023, 2023.

[0006] These known distribution coefficients allow a simple conversion of the concentration of a target analyte in the gaseous sample, especially in the headspace, into liquid concentration (concentration of the target analyte in the liquid (matrix)).

[0007] For more complex sample compositions, such as water, ethanol, and methanol, such partition coefficients are generally unavailable and must be determined empirically for each specific sample composition, making headspace analysis difficult or even impossible. This is particularly problematic for applications or measurement series where the composition of the liquid under investigation is not constant, for example, changing water-ethanol ratios during distillation.

[0008] The object underlying the invention is to provide a method by which the above disadvantages in a headspace analysis of liquid sample compositions with several chemical compounds can be reduced or avoided.

[0009] This object is achieved by a method and a gas detection device having the features of the respective independent patent claim. Advantageous embodiments with useful further developments are specified in the dependent patent claims.

[0010] A method is therefore proposed for determining the concentration of at least one target analyte in a liquid, wherein the liquid contains at least one further chemical compound, comprising the steps of: taking a gaseous sample composition from a region located in the vicinity of, in particular above, the liquid; determining a quantitative measurement signal of the target analyte in the gaseous sample composition; converting the measurement signal of the target analyte determined in the gaseous sample composition into a concentration of the target analyte in the liquid by means of an adaptation function.It is provided that the method comprises the further steps of: determining or entering at least one characteristic value of the at least one further chemical compound of the liquid; wherein the measurement signal of the target analyte and the at least one characteristic value of the at least one further chemical compound of the liquid are used as input parameters for the adaptation function.

[0011] The sensor signal or measurement signal of the target analyte is converted into the corresponding concentration of the target analyte in the liquid using a fitting function. In addition to the functional relationship between the measurement signal and the concentration, the fitting function also takes into account the functional relationship between the concentration in the gaseous and liquid sample using corresponding distribution coefficients.

[0012] For measurements of liquids with different compositions, in addition to the sensor signal of the target analyte, additional input parameters containing information on the composition of the liquid are required for the adaptation function to correctly determine the concentration of the target analyte in the liquid. This is achieved by the method proposed here. The proposed method thus enables simple and automated analysis of target analytes in liquid samples with varying sample compositions. This is achieved by considering not only the headspace concentration of at least one target analyte, but also at least one other characteristic value of at least one other chemical compound (matrix component).From the knowledge of the quantitative measurement signal of the target analyte and the characteristic value of the at least one further chemical compound as well as their individual distribution coefficients depending on the liquid sample composition, the correct concentration of the at least one target analyte in the liquid sample can be calculated from the determined or measured value of the concentration of the target analyte in the gaseous sample composition using the fitting function.

[0013] Thus, the concentration of the target analyte in the liquid can be accurately quantified regardless of the composition of the liquid sample.

[0014] In the method, the adaptation function can be configured to adapt a measurement signal of the target analyte determined in the gaseous sample composition as a function of the at least one characteristic value of the further chemical compound in the liquid.

[0015] Such a characteristic of the further chemical compound can be, for example, its concentration in the liquid or gaseous sample composition. Such a characteristic can also be, for example, the color, mass density, electrical conductivity, heat capacity, thermal conductivity, refractive index, or pH value of the liquid.

[0016] In the method, the at least one characteristic value of the at least one further chemical compound can be provided by a user when carrying out the method and / or determined in the gaseous sample composition as a further measurement signal; and / or measured directly in the liquid.

[0017] In the method, the input parameters and / or further parameters of the adaptation function can be provided or improved by means of a calibration using liquids with a known composition which contain at least the target analyte and in particular which contain at least one further chemical compound.

[0018] In the method, the fitting function can be determined using a first liquid with a known first composition having a first content of the target analyte and having a first content of the at least one further chemical compound, and a second liquid with a known second composition having a second content of the target analyte and having a second content of the at least one further chemical compound.

[0019] In the method, the partition coefficient associated with the target analyte for the first liquid and for the second liquid can be known during calibration.

[0020] In the method, the liquid can be contained in a container and the gaseous sample composition can be taken from a headspace formed in the vicinity, in particular above the liquid in the container.

[0021] Further proposed is a gas detection device comprising at least one gas detector configured to quantify at least one target analyte in a gaseous sample composition and to output a corresponding measurement signal; and comprising a control unit configured to carry out the method described above.

[0022] The gas detector can be a sensor, in particular a chemo-resistive, capacitive, potentiometric, amperometric, thermal, thermochemical, thermal-physical, gravimetric, optical, or biochemical gas sensor. However, the gas detector can also be a flame ionization detector, a mass spectrometer, or an infrared spectrometer.

[0023] The gas detection device can be connected directly or indirectly to a container containing the liquid and can be connected to carry out the method.

[0024] The gas detection device may have a gas inlet and gas outlet, with a conveying unit which takes the gaseous sample from the headspace and conveys it to the at least one gas detector for carrying out the method.

[0025] The gas detection device may further comprise: a separation column arranged between the gas inlet and the gas outlet, which is configured to separate molecules contained in the gaseous sample; at least one conveying device, in particular a pumping device, which is configured to actively convey the gaseous sample from the gas inlet to the gas outlet through the separation column. The pump may be, among others, a diaphragm pump, a rotary piston pump, a piston pump, or a peristaltic pump.

[0026] The gas detection device can have an input unit configured to allow a user to enter or select one or more parameters related to the liquid. The input unit could be, for example, a keyboard or a touchscreen. Wireless transmission of parameters (e.g., Bluetooth or Wi-Fi) to the control unit via an external input unit such as a smartphone or computer is also conceivable.

[0027] In addition to the at least one gas detector, the gas detection device can contain additional detectors and sensors for determining characteristic values ​​of the liquid. The determination of the additional characteristic values ​​of the liquid can be carried out simultaneously or sequentially with the measurement of the gaseous sample. Examples of additional detectors and sensors include a U-shaped oscillator for measuring the density of the liquid, a pH meter for determining the pH value of the liquid, several electrodes, in particular a pair of electrodes, for determining the electrical conductivity of the liquid, and an optical sensor for determining the color or transparency of the liquid.

[0028] In particular, a gas detection device as known from WO 2020 144 059 A1 can be used as the gas detection device.

[0029] In particular, a gas detection device such as that described in the German application filed at the same time by the same applicant with the title “Gas detection device with temperature-dependent flow rate control and method for determining a chemical compound by means of such a gas detection device” can also be used as the gas detection device.

[0030] Further advantages and details of the invention will become apparent from the following description of embodiments with reference to the figures.

[0031] Fig. 1 is a simplified and schematic representation of an example of a gas detection device;

[0032] Fig. 2 is a simplified representation of a method for determining the concentration of at least one target analyte in a liquid present in a container;

[0033] Fig. 3 is a simplified and schematic diagram illustrating measured concentrations in a gaseous sample composition and explaining the method. In Fig. 1, a simplified and schematic representation of a gas detection device 10 is shown as an example, a rectangle. The rectangle can also be understood as the housing 12 of the gas detection device 10.

[0034] The gas detection device 10 is configured to determine at least one target analyte in a gaseous sample composition, which is simplified as a white contour arrow gP.

[0035] The gas detection device has a gas inlet 14 and a gas outlet 16. A separation column 18 is arranged between the gas inlet 14 and the gas outlet 16, which is designed to separate molecules contained in the gaseous sample composition gP. The separation column 18 is highlighted here in a simplified manner with a dotted pattern.

[0036] Furthermore, the gas detection device 10 comprises at least one gas detector 20, which is configured to quantify the at least one target analyte after passing through the separation column 18. In particular, the concentration of the at least one target analyte in the gaseous sample composition gP can be determined.

[0037] The flow through the separation column 18 is achieved by generating an active gas flow. For this purpose, the gas detection device 10 can have at least one conveying device 22 configured to actively convey the gaseous sample gP from the gas inlet 14 to the gas outlet 16 through the separation column 18.

[0038] In Fig. 1, the conveying device 22 is shown as an example as a pumping device.

[0039] The position of the conveying device 22 shown here (downstream of the separation column 18) is purely exemplary. It can also be arranged upstream of the separation column 18 with respect to the flow direction of the gaseous sample gP. The gas detection device 10 further comprises a control unit 24 which is configured to control the conveying device 22.

[0040] For example, a flame ionization detector or a gas sensor, such as an optical sensor, metal oxide sensor or the like, can be used as the gas detector 20.

[0041] The gas detection device shown in Fig. 1 shows one possible embodiment. It should be noted that a gas detection device with fewer components can also be used to carry out the method described in more detail below.

[0042] In particular, it may be sufficient if the gas detection device comprises a gas detector 20 and a control unit 24. This may be the case, for example, with a gas detection device having an optical sensor as the gas detector 20.

[0043] In other words, in certain embodiments, the gas inlet 14, gas outlet 16, separation column 18 and conveying device 22 do not represent mandatory features that must be present in a gas detection device in order to carry out the method according to the invention.

[0044] The gas detection device 10 can also have a display and / or input device 28. This can, for example, have a display and / or several buttons. Combined functionality is also conceivable, for example in the form of a touchscreen. Such a display device 28 can, for example, display results of the determination of the at least one chemical compound and / or a time sequence symbol while the gaseous sample gP flows through the separation column 18.

[0045] The input device 28 can, for example, be used by the user to enter or specify characteristic values ​​of other chemical compounds of the liquid, for example sugar-salt content of the sample, type of beverage (beer, wine, liquor) and the like.

[0046] The gas detection device 10 can have an energy storage unit 32, for example in the form of a rechargeable battery, for supplying energy to the control unit 24 and the conveying device 22 connected thereto as well as to the gas detector 20 and / or further optional sensors not shown here.

[0047] For charging the energy storage unit 32 and / or for external power supply and / or for data communication, the gas detection device 10 can have at least one interface 34. Such an interface 34 can be wired or wireless. Reference is made purely as examples to the following interfaces: USB, Bluetooth, WLAN. Even though only one interface 34 is symbolically represented in Fig. 1, the gas detection device 10 can also have multiple interfaces, in particular a wired and a wireless interface.

[0048] The control unit 24 is configured to perform a method 500, which is described in more detail below with reference to Fig. 2.

[0049] The method 500 serves to determine the concentration of at least one target analyte ZA in a liquid 52, wherein the liquid 52 contains at least one further chemical compound (CV). Even though the method does not necessarily have to be carried out in conjunction with a container 50 shown, such an embodiment variant is described in more detail below.

[0050] According to the method, in a step S501, a gaseous sample composition gP is taken from a region located near, in particular above, the liquid 52, in particular a headspace 54 formed in the container 50, which can also be referred to as headspace. According to a step S502, a quantitative measurement signal of the target analyte ZA in the gaseous sample composition gp is determined.

[0051] In a step S503, at least one characteristic value of the at least one further chemical compound CV of the liquid 52 is determined or entered.

[0052] According to a step S504, the measurement signal of the target analyte ZA determined in the gaseous sample composition gP is converted into a concentration of the target analyte ZA in the liquid 52 by means of an adaptation function AF.

[0053] In the conversion according to step S504, a provided adaptation function AF is used, which uses the measurement signal of the target analyte ZA and the at least one characteristic value of the liquid 52 as input parameters

[0054] In the method 500, the adaptation function AF is configured to adapt a measurement signal of the target analyte ZA measured in the gaseous sample composition gP as a function of the at least one characteristic value of the further chemical compound CV in the liquid 52.

[0055] In the method 500, in step S503, the at least one characteristic value of the at least one further chemical compound (CV) can be provided by a user when carrying out the method, and / or determined in the gaseous sample composition (gP) as a further measurement signal, and / or measured directly in the liquid.

[0056] In the method 500, the input parameters and / or further parameters of the adaptation function AF can be provided or improved based on a calibration (S505) using liquids with a known composition, which contain at least the target analyte ZA and can contain at least one further chemical compound CV.

[0057] The adaptation function AF can be determined, for example, using a first liquid with a known first composition with a first content of the target analyte ZA and with a first content of the at least one further chemical compound CV, and a second liquid with a known second composition with a second content of the target analyte ZA and with a second content of the at least one further chemical compound CV.

[0058] In calibration S505, the partition coefficient assigned to the target analyte ZA can be known for the first liquid and for the second liquid.

[0059] According to the method 500 described above, the individual quantitative measurement signals of the target analyte ZA and the further chemical compound CV in the gaseous sample composition gP in the headspace 54 can be determined, for example, using the gas detector 20. The measurement signal of the further chemical compound serves as a characteristic value.

[0060] The control unit 24 stores the calibration of the gas detector and the functional relationship between the individual ratio coefficients and the sample composition, referred to here as the adaptation function AF. Given the quantitatively determined measurement signal of the target analyte ZA in the gaseous sample gP and at least one characteristic value of another chemical compound CV (matrix component), a calculation or conversion into the concentration of the target analyte ZA in the liquid 52 is performed.

[0061] The method 500 generally described above will be explained using an example, which is illustrated in Fig. 3. The example in Fig. 3 relates to alcoholic beverages. One application of the proposed invention is described as an example, namely the measurement of toxic methanol (a byproduct of alcoholic fermentation) in alcoholic beverages.

[0062] Figure 3 shows, as an example, the chromatographic headspace measurement of three liquid samples, all containing the same concentration of methanol (0.1 vol.% in liquid) in different sample compositions or sample matrices. In addition to the constant 0.1 vol.% methanol, these sample compositions contain 5 vol.% (solid line), 40 vol.% (dashed line), or 80 vol.% (dashed-dotted line) ethanol in water.

[0063] The diagram shown in Fig. 3 shows the time on the horizontal x-axis and a detector signal of the gas detector 20 on the vertical y-axis, which illustrates the concentration of the target analyte (ZA) methanol and the further chemical compound (CV) ethanol in the gaseous sample composition.

[0064] Although the methanol concentration for these samples is the same in the liquid phase, namely 0.1 vol.%, the methanol concentration in their headspace 54, i.e. in the gaseous sample composition, increases with increasing ethanol concentration in the liquid (sample matrix), which can be seen from the curves in the diagram at a time of around 50 seconds.

[0065] In the gaseous sample composition, at an ethanol content of 80 vol.% in the liquid, a methanol concentration is measured or determined that is approximately 1.4 times the methanol concentration in the gaseous sample composition at an ethanol content of 5 vol.% in the liquid, even though the liquid always contains the same methanol content of 0.1 vol.%. Thus, the methanol concentration determined in the gaseous sample composition cannot be used to simply determine the (correct) methanol content in the liquid.

[0066] However, the measurement quantifies not only methanol (as the target analyte ZA) in the gas phase, but also ethanol (as another chemical compound CV). In this example, the sample matrix essentially contains only ethanol and water, with the methanol concentration being so low that the ethanol distribution coefficient is not affected or only negligibly.

[0067] Thus, the ethanol concentration measured in the gaseous sample composition (quantitative measurement signal) can be directly converted into the concentration of ethanol in the liquid sample using the calibration of the detector and a constant partition coefficient (ethanol-water) tabulated in the literature.

[0068] From this, the methanol concentration in the liquid can be determined using a fitting function AF, which uses the measured methanol signals in the headspace and the ethanol concentration in the liquid as input parameters. Consequently, the same methanol concentration in the sample is predicted, particularly based on the fitting function.

[0069] The described example can be represented in a table as follows:

[0070] What has been described above with reference to Figures 1 to 3 can, for example, be used in a portable device (gas detection device 10) for detecting methanol in ethanol-water mixtures. The detector (20 in Figure 1) selectively measures both methanol and ethanol in the headspace of liquid samples.

[0071] Since the methanol concentration is typically low (<2 vol%), it can be neglected for the correct quantification of ethanol. The measured ethanol concentration in the headspace is therefore directly converted to the corresponding concentration in the liquid sample using the calibration curve (adaptation function AF) stored in the device.

[0072] If the liquid sample composition (matrix composition; ethanol-water ratio) is known, the measured methanol headspace sensor signal (measurement signal) can be converted into the corresponding concentration in the liquid sample via the adaptation function stored in the control unit (24 in Fig. 1).

[0073] The adjustment functions for methanol and ethanol are determined by measuring two calibration liquids containing different concentrations of methanol (between 0.05-2 vol%) and ethanol (between 20 and 100 vol%) in water.

[0074] Since the matrix composition of calibration fluids is known a priori, the corresponding partition coefficients for correlating the methanol headspace concentration with the concentration in the liquid are also determined a priori and incorporated into the algorithm for calculating the correct fitting function. As a result, the detector correctly quantifies the methanol concentration in liquid samples or sample matrices with different ethanol-to-water ratios using the same instrument calibration. For example, the instrument is first calibrated with two provided calibration fluids, so that after calibration, the methanol concentration in samples containing 20, 40, and 80 volume percent ethanol in water is correctly predicted using the fitting function.

[0075] Another example without a figure is described below.

[0076] Headspace concentrations also depend on the concentration of solutes (e.g. salt or sugar) contained in a sample fluid.

[0077] The functional relationship depends on the type of analyte (e.g. methanol), the liquid sample composition (matrix; e.g. water) and the solute (e.g. salt).

[0078] For example, a seawater sample containing 100 ppm (mg / L) methanol and a salt concentration of 35 g / L has a methanol concentration in the gaseous sample composition (headspace) that is approximately 15% higher than the headspace concentration in a sample with the same methanol concentration in pure water.

[0079] One embodiment of this invention may be a gas detection device (see also Fig. 1 and the related description above) for measuring the methanol concentration in water samples with varying salt concentrations. The device is calibrated with headspace samples of varying methanol concentrations in pure water. The gas detection device also stores the functional relationship between the sample's salt concentration and the partition coefficient between the methanol headspace and liquid concentration.

[0080] A water sample with any methanol and salt concentration is measured using the gas detection device, with the salt concentration entered (by a user) as a parameter. The gas detection device measures the methanol concentration in the headspace and calculates the corresponding correct concentration in the liquid using the internally stored functional relationship (fitting function) between the partition coefficient and salt concentration. As a result, the device correctly predicts the methanol concentration regardless of the sample's salt content.

[0081] In a further embodiment, the salt content could be measured simultaneously by the gas detection device (e.g. via a density measurement).

[0082] The described example can be presented in tabular form as follows

[0083] Another application example involves the measurement of methanol in soft drinks after cold sterilization with dimethyl dicarbonate. Dimethyl dicarbonate is added to beverages before bottling and canning to sterilize and stabilize the beverage. Dimethyl dicarbonate decomposes into methanol and water within a few hours. The correct dosage of dimethyl dicarbonate can therefore be determined by determining the methanol content of the beverages.

[0084] Soft drinks often have an increased sugar content of up to 400 g / L, which strongly influences the distribution coefficient of methanol in the headspace (analogous to that described above for salt).

[0085] One embodiment of this invention can be a gas detection device that allows the user to enter the sugar content before, during, or after a measurement. The sugar content serves as a (further) characteristic value of the liquid for the implementation of the method and flows into the stored adjustment function as an input parameter. Thus, the correct methanol concentration is output regardless of the sugar content of the measured liquid.

[0086] Alternatively, the sugar content could also be determined by another detector, e.g. by measuring the density or refractive index of the liquid.

Claims

PATENT CLAIMS: 1 . Method (500) for determining the concentration of at least one target analyte (ZA) in a liquid (52), wherein the liquid (52) contains at least one further chemical compound (CV), comprising the steps: Taking (S501) a gaseous sample composition (gP) from a region located near, in particular above, the liquid (52), Determining (S502) a quantitative measurement signal of the target analyte (ZA) in the gaseous sample composition (gP); Determining (S503) or entering at least one characteristic value of the at least one further chemical compound (CV) of the liquid (52); Converting (S504) the measurement signal of the target analyte (ZA) determined in the gaseous sample composition (gP) into a concentration of the target analyte (ZA) in the liquid (52) by means of an adaptation function (AF), wherein the measurement signal of the target analyte (ZA) and the at least one characteristic value of the at least one further chemical compound (CV) of the liquid (52) are used as input parameters for the adaptation function (AF).

2. The method (500) according to claim 1, wherein the adaptation function (AF) is configured to adapt a measurement signal of the target analyte (ZA) determined in the gaseous sample composition (gP) as a function of the at least one characteristic value of the further chemical compound (CV) in the liquid (52).

3. Method according to claim 1 or 2, wherein the at least one characteristic value of the at least one further chemical compound (CV): is provided by a user when carrying out the method and / or in the gaseous sample composition (gP) is determined as an additional measurement signal; and / or is measured directly in the liquid.

4. Method (500) according to one of the preceding claims, wherein the input parameters and / or further parameters of the adaptation function (AF) are provided or improved on the basis of a calibration (S505) using liquids with a known composition which contain at least the target analyte (ZA) and in particular which contain at least one further chemical compound (CV).

5. The method according to claim 4, wherein the fitting function (AF) is determined using a first liquid with a known first composition with a first content of the target analyte (ZA) and with a first content of the at least one further chemical compound (CV), and a second liquid with a known second composition with a second content of the target analyte (ZA) and with a second content of the at least one further chemical compound (CV).

6. The method (500) according to claim 5, wherein during the calibration (S505) the distribution coefficient associated with the target analyte (ZA) is known for the first liquid and for the second liquid.

7. The method (500) according to any one of the preceding claims, wherein the liquid is contained in a container (50) and the gaseous sample composition (gP) is withdrawn from the headspace (54) formed in the container (50).

8. Gas detection device (10) with at least one gas detector (20) which is designed to detect at least one target analyte in a gaseous sample composition. tion (gP) and to output a corresponding measurement signal; a control unit (24) which is configured to carry out the method according to one of the preceding claims.

9. Gas detection device (10) according to claim 8, characterized in that it is further connectable directly or indirectly to a container (50) containing the liquid (52) and is connected for carrying out the method (500).

10. Gas detection device (10) according to claim 8 or 9, further comprising a gas inlet (14) and a gas outlet (16) and a separation column (18) arranged between the gas inlet (14) and the gas outlet (16), which is configured to separate molecules contained in the gaseous sample (gP); at least one conveying device (22), in particular a pumping device, which is configured to actively convey the gaseous sample (gP) from the gas inlet (14) to the gas outlet (16) through the separation column (18); wherein the control unit (24) is configured to control the conveying device (22), and wherein the gas detector (22) is arranged downstream of the separation column (18).

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