Gas detection device with temperature-based flow rate control, and method for determining a chemical compound using such a gas detection device

Abstract

The invention relates to a gas detection device (10) which is designed to determine at least one chemical compound in a gaseous sample (gP), comprising a gas inlet (14) and a gas outlet (16); a separating column (18) between the gas inlet (14) and the gas outlet (16), said separating column being designed to separate molecules contained in the gaseous sample (gP); at least one gas detector (20) which is designed such that the at least one chemical compound is quantified after passing through the separating column (18), in particular the concentration of the at least one chemical compound in the gaseous sample is determined; at least one conveyor device (22) which is designed to actively convey the gaseous sample (gP) from the gas inlet (14) to the gas outlet (16) through the separating column (18); a control unit (24) which is designed to actuate the conveyor device (22); and at least one temperature sensor (26) which is designed to detect the state temperature in the region of the separating column (18) or in the separating column (18). According to the invention, the control unit (24) is designed to actuate the conveyor device (22) on the basis of the detected state temperature. The invention additionally relates to a method for quantitatively determining a chemical compound in a gaseous sample.

Description

[0001] Gas detection device with temperature-dependent flow rate control and method for determining a chemical compound by means of such a gas detection device

[0002] DESCRIPTION:

[0003] The invention relates to a gas detection device configured to determine at least one chemical compound in a gaseous sample, comprising a gas inlet and a gas outlet; 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 gas detector configured to quantify the at least one chemical compound after it has passed through the separation column, in particular to determine the concentration of the at least one chemical compound in the gaseous sample; at least one conveying device configured to actively convey the gaseous sample from the gas inlet to the gas outlet through the separation column; a control unit configured to control the conveying device;and at least one temperature sensor configured to detect a state temperature in the region of the separation column or in the separation column. Furthermore, the invention relates to a method for the quantitative determination of a chemical compound in a gaseous sample.

[0004] Such a gas detection device is known, for example, from DE 10 2019 100 587 A1.

[0005] In gas chromatography, molecules are separated over time in a chromatographic separation column and then sequentially quantified by a detector. If the various analytes or chemical compounds present in the sample are sufficiently separated, the detector can be nonspecific because the analytes do not need to be identified but only quantified at the specific times (retention times) at which they have passed through the separation column. The retention times of the analytes depend heavily on the physicochemical interaction between the analyte molecules and the material and type of separation column used. Furthermore, the retention time is a function of the flow rate or volume of the carrier gas that transports the sample through the column to the detector, and the temperature of the separation column.If the temperature of the column is not kept constant within a narrow temperature range, the separation of different analytes is not guaranteed and the retention times of the analytes fluctuate greatly, resulting in low reproducibility of the measurements.

[0006] The object underlying the invention is to provide a gas detection device with a separation column and a method for the quantitative determination of a chemical compound in a gaseous sample, which can be used independently of a narrow temperature range and at different locations.

[0007] This object is achieved by a gas detection device and a method having the features of the respective independent patent claims. Advantageous embodiments with useful further developments are specified in the dependent patent claims.

[0008] What is proposed is a gas detection device which is designed to determine at least one chemical compound in a gaseous sample, comprising a gas inlet and a gas outlet; a separation column arranged between the gas inlet and the gas outlet, which is designed to separate molecules contained in the gaseous sample; at least one gas detector which is designed to quantify the at least one chemical compound after it has passed through the separation column, in particular to determine the concentration of the at least one chemical compound in the gaseous sample; at least one conveying device which is designed to actively convey the gaseous sample from the gas inlet to the gas outlet through the separation column; a control unit which is designed to control the conveying device;and a temperature sensor configured to detect a state temperature in the region of the separation column or in the separation column. The control unit is configured to control the conveying device depending on the detected state temperature.

[0009] This allows flexible use of the gas detection device at locations with changing (ambient) temperatures or different locations with different (ambient) temperatures, whereby instead of a separation column with essentially constant temperature, the delivery volume or flow velocity (flow rate) can be adjusted, so that temperature-related effects when determining the chemical compound can be almost excluded.

[0010] By means of the temperature sensor, the current temperature in the area of ​​the separation column can be determined before or during the determination of a chemical compound in a gaseous sample, so that the state temperature is available depending on the location of the gas detection device and the ambient conditions there.

[0011] The at least one temperature sensor can be, for example, a thermocouple, an RTD (resistance temperature detector), a thermistor, a semiconductor-based sensor, a thermostat or an infrared sensor.

[0012] The temperature sensor can be configured to determine a change in temperature in the region of the separation column with an accuracy of ±2°C or better. The temperature can be measured continuously, for example, or within five minutes or less before the start of a determination of the at least one chemical compound.

[0013] The gas detection device may be designed as a portable device.

[0014] In other words, the gas detection device can be a device held in one hand during measurement. For the purposes of this application, the term "portable" means that the gas detection device is designed, in terms of its weight and / or external dimensions, such that it can be held and operated by a person with one or both hands.

[0015] The gas detection device can also be designed as a stationary device. A stationary gas detection device, like a portable device, can be designed to be compact in terms of its dimensions.

[0016] For example, a stationary gas detection device can be designed so that it can be positioned and set up in one location, but due to its compact dimensions, it can be easily transported so that it can be set up and used again at another location.

[0017] The outer dimensions can, for example, be within an imaginary cuboid surrounding the gas detection device, with a length of 10 cm to 50 cm, a width of 2 cm to 30 cm, and a height of 2 cm to 20 cm. The volume occupied by a housing of the gas detection device can therefore, for example, range from 40 cm 3 up to 30,000cm 3 be.

[0018] The weight can, for example, range from 25g to 20,000g, in particular 250g to 750g.

[0019] The temperature sensor can be located, for example, a few millimeters or centimeters away from the separation column or directly on its housing. The temperature sensor can be located, for example, in a housing of the gas detection device in which the separation column is also arranged or housed.

[0020] The control unit can be configured to adjust the conveying volume of the conveying device as a function of the detected state temperature, such that the gaseous sample is conveyed from the gas inlet to the gas outlet at different state temperatures with different flow velocities.

[0021] As already mentioned, this enables the flexible use of the gas detection device in locations with changing (ambient) temperatures or different locations with different (ambient) temperatures, whereby instead of a separation column with an essentially constant temperature, an adjustment of the delivery volume or the flow velocity (flow rate) can be carried out, so that temperature-related effects when determining the chemical compound can be almost excluded.

[0022] In the gas detection device, the control unit can be configured to control the conveying device such that the quantitative determination of the at least one chemical compound is completed for each detection process of such a chemical compound after a predetermined, substantially constant period of time since the start of the detection process. The constant period of time should refer in particular to the time of detection or the retention time of the chemical compound. The output of a measurement result on a display or a device connected to the gas detection device is not included in this period of time.

[0023] In other words, by taking the state temperature into account, the conveying device can be set to a conveying volume or flow rate that results in a result being available after a predetermined and essentially constant period of time for each detection or measurement process. For the gas detection device, it can therefore be assumed, even before a measurement or determination of a chemical compound is to be carried out, that the desired measured value will be available after the known (predetermined) period of time. The control unit can, for example, have stored information (formula, lookup table, or the like) that serves to set the conveying device to a conveying volume or flow rate depending on an input variable from the at least one temperature sensor.

[0024] The control unit may also be configured to use current and previously stored temperature input variables from the at least one temperature sensor so that a temperature of the separation column can be predicted during the determination of the at least one chemical compound.

[0025] The input variable from the temperature sensor can, for example, be the current temperature of the separation column. Alternatively, it can also be a current change in the temperature of the separation column or / and the temperature trend of the separation column over a certain period of time.

[0026] In the case of the gas detection device, the time duration can be approximately 10 to 600 seconds, in particular approximately 40 to 120 seconds. In particular, it is intended that the time duration Tdet lies within a narrow time window, for example, Tdet ± 15 seconds, in particular ± 5 seconds.

[0027] A concrete example, which does not have to be understood as restrictive, can be described as follows: The determination of a chemical compound in a gaseous sample can be completed after, for example, 37 to 43 seconds, i.e., for example, Tdet = 40 seconds ± 3 seconds.

[0028] In the gas detection device, the state temperature can be from -10°C to 50°C, in particular from 10°C to 35°C.

[0029] The gas detection device can comprise at least one sensor, for example, a pressure sensor, whose signal allows the flow volume through the separation column to be quantified. This allows the determination and maintenance of a desired flow volume or flow rate of the gaseous sample to be optimized.

[0030] An optional pressure sensor is configured to detect the pressure prevailing in the flow path between the separation column and the conveying device. This allows for the optimization of determining and maintaining a desired conveying volume or flow rate of the gaseous sample. In particular, the control unit can be configured to also control the conveying device taking the detected pressure into account.

[0031] With the gas detection device, the chemical compound to be determined can be methanol, ethanol, acetone, isoprene, formaldehyde, benzene, ammonia, acetic acid, or hydrogen cyanide. Please note that the chemical compounds mentioned here are not an exhaustive list. Rather, a gas detection device with a separation column and temperature sensor can also be used to determine other chemical compounds.

[0032] The gas detection device can be used in particular in the following specialist areas: breath analysis and / or gas space analysis and / or air monitoring.

[0033] A flame ionization detector or a gas sensor, such as an optical sensor, metal oxide sensor, electrochemical sensor, or the like, can be used as a gas detector. The metal oxide sensor can, in particular, be a sensor with an active sensor material made of tin oxide, tungsten oxide, zinc oxide, or titanium oxide.

[0034] The delivery device can, for example, be a pumping device. The delivery volume can be controlled directly via the pumping device. The pumping device can be, among other things, a diaphragm pump, a rotary piston pump, a piston pump, or a peristaltic pump. The delivery device can, for example, be formed by a pumping device in combination with an adjustable outlet valve or mass flow controller. In such a case, the delivery volume can be controlled by controlling the outlet valve or the mass flow controller and / or the pumping device.

[0035] The conveying device can in particular be designed to convey a carrier gas or carrier gas mixture to which the gaseous sample is added.

[0036] It is also conceivable for the conveying device to be formed by a pressure vessel with an adjustable or controllable outlet valve or mass flow controller, from which pressurized carrier gas flows, to which the gaseous sample is mixed. In such a case, the adjustable outlet valve or mass flow controller can be adjusted depending on the measured temperature.

[0037] The carrier gas can be, for example, (purified) air, an inert gas such as nitrogen, or the like. If the carrier gas is air, it can be either direct room air or room air purified by a zero-air filter. A zero-air filter could, for example, be a packed bed of adsorbent, such as activated carbon, zeolite, silica, or a mixture of at least two such filter materials.

[0038] The separation column can be a gas chromatography column or a type of filter device with adsorbent materials, in particular with a packed bed of polymer adsorbent such as Tenax TA.

[0039] Also proposed is a method for the quantitative determination of a chemical compound in a gaseous sample, comprising the steps of: detecting a state temperature in the region of or in a separation column; determining a delivery volume as a function of the detected state temperature; adjusting a delivery device to the determined delivery volume and conveying the gaseous sample with the delivery volume through the separation column from a gas inlet to a gas outlet; detecting the at least one chemical compound after a predetermined period of time, which period remains substantially the same for each detection process of such a chemical compound, since the start of the detection process.

[0040] The process can be carried out at a temperature of -10°C to 50°C, in particular from 10°C to 35°C. In other words, the process can be carried out particularly at normal ambient or indoor temperatures.

[0041] The procedure can be carried out during the period of about 10 to 600 seconds, in particular about 40 to 120 seconds.

[0042] The described method may include further steps, which are also disclosed in particular by the structure of the gas detection device described above. The method can therefore be carried out by means of or using the gas detection device described above. In other words, the gas detection device described above is particularly configured to carry out the method described above.

[0043] The field of application of the gas detection device or method described above can be very diverse. In particular, the following are conceivable: detection of biomarkers in breath, especially exhaled air; detection of chemical compounds, especially toxic ones, in ambient air, exhaust gases, or general environmental monitoring; detection of analytes in liquids (vapor space analysis), such as the detection of methanol in liquids, especially in containers containing alcoholic beverages.

[0044] Further advantages and details of the invention will become apparent from the following description of embodiments with reference to the figures. Figure 1 shows a simplified and schematic representation of an example of a gas detection device;

[0045] Fig. 2 is a simplified representation of a method for determining a chemical compound;

[0046] Fig. 3 shows a comparison diagram for the determination of methanol as an example of a chemical compound;

[0047] Fig. 4 a comparison diagram for the determination of acetone as an example of a chemical compound.

[0048] In Fig. 1, a simplified and schematic representation of a gas detection device 10 is shown as a rectangle. The rectangle can also be understood as the housing 12 of the gas detection device 10.

[0049] The gas detection device 10 is designed to determine at least one chemical compound in a gaseous sample, which is simplified as a white contour arrow gP.

[0050] 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 the molecules contained in the gaseous sample gP. The separation column 18 is highlighted here in a simplified manner with a dotted pattern.

[0051] Furthermore, the gas detection device 10 comprises at least one gas detector 20, which is configured to quantify the at least one chemical compound after it has passed through the separation column 18. In particular, the concentration of the at least one chemical compound in the gaseous sample gP can be determined.

[0052] 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.

[0053] In Fig. 1, the conveying device 22 is shown as an example as a pumping device.

[0054] 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.

[0055] The gas detection device 10 further comprises a control unit 24 which is configured to control the conveying device 22.

[0056] The gas detection device 10 has at least one temperature sensor 26 configured to detect a state temperature in the region of the separation column 18 or in the separation column 18. It should be noted that a temperature sensor 26 can be arranged at different locations in the gas detection device 10 or along the separation column 18. This is illustrated purely by way of example by the dotted rectangles with the reference numeral 26.

[0057] It is also possible for the gas detection device 10 to have, for example, two temperature sensors 26 at different locations on the gas detection device 10, so that their respective detected temperature values ​​can be averaged or weighted and used further.

[0058] The temperature of the separation column 18 can therefore either be measured with a temperature probe / temperature sensor 26 directly inside or outside the separation column or approximated by another temperature measurement performed by the gas detection device 10 (e.g., measurement of the ambient temperature). 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 touch-sensitive display (touchscreen). On such a display device 28, for example, results of the determination of the at least one chemical compound and / or a time sequence symbol can be displayed while the gaseous sample gP flows through the separation column 18.

[0059] The gas detection device 10 may have at least one further sensor 30 which is configured to quantify the flow volume through the separation column 18.

[0060] This can be, for example, a flow sensor that directly determines the conveyed volume in the flow path upstream or downstream of the separation column 18. It can also be, for example, a pressure sensor that detects, for example, a pressure prevailing in the flow path between the separation column 18 and the conveying device 22, from which a corresponding conveyed volume can be calculated or derived.

[0061] 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 various (optional) sensors 20, 26, 30.

[0062] 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. In the gas detection device 10, the control unit 24 is configured to control the conveying device 22 depending on the detected state temperature.

[0063] The control unit 24 can receive a measured value for the state temperature from the at least one temperature sensor 26. The state temperature can, for example, be adopted directly or, depending on the position of the temperature sensor 26 in / on the gas detection device 10, it can be subjected to an (empirical) correction before being further processed.

[0064] The control unit 24 is configured to adjust the delivery volume of the delivery device 22 depending on the detected temperature. The gaseous sample gP is delivered from the gas inlet 14 to the gas outlet 16 at different flow velocities at different temperatures.

[0065] The control unit can in particular be configured to control the conveying device 22 in such a way that the quantitative determination of the at least one chemical compound is present in each detection process of such a chemical compound after a predetermined, substantially constant period of time since the start of the detection process.

[0066] Fig. 2 shows a simplified and schematic flow diagram of a method 500 for the quantitative determination of a chemical compound in a gaseous sample, in particular using a gas detection device 10 described above.

[0067] In the method 500, in a step S501, a state temperature in the region or in a separation column 18 is detected.

[0068] In step S502, a delivery volume is determined as a function of the detected state temperature. In step S503, the delivery device 22 is adjusted to the determined delivery volume, and the gaseous sample gP is delivered at the delivery volume through the separation column 18 from the gas inlet 14 to the gas outlet 16.

[0069] According to a step S504, the at least one chemical compound is detected after a predetermined period of time, which remains substantially the same for each detection process of such a chemical compound, since the start of the detection process.

[0070] The method 500 can be carried out in particular at a state temperature of -10°C to 50°C, in particular of 10°C to 35°C.

[0071] The method 500 can be carried out during a period of approximately 10 to 600 seconds, in particular approximately 40 to 120 seconds.

[0072] With the gas detection device 10 and / or the method 500 described above, in particular methanol or ethanol or acetone can be provided as the chemical compound to be determined.

[0073] A functional relationship, not explicitly shown in the process steps, between the state temperature of the separation column 18 and the flow rate of the gaseous sample to maintain the retention time of the analytes constant is stored in the device software of the control unit 24. For a given temperature input (state temperature), the control unit calculates the required flow rate of the gaseous sample, which is then controlled by the conveying device 22.

[0074] Figures 3 and 4 show two test examples conducted using the same gas detection device 10. Figure 3 relates to the determination of methanol as a chemical compound, while Figure 4 relates to the determination of acetone as a chemical compound. In Figures 3 and 4, time is plotted in seconds on the horizontal x-axis. The measured concentration of the respective chemical compound (methanol or acetone) is plotted on the vertical y-axis in a standardized manner.

[0075] In the gas detection device 10 used, a miniature vacuum pump serves as the conveying device 22 and flow regulator. A packed bed of 200 mg polymer adsorbent (Tenax TA) serves as the separation column 18. A sensor 20 for volatile organic compounds (VOC) is used.

[0076] Sampling was performed in the same way for all measurements by taking 10 ml of saturated headspace samples from a vial. For the example in Fig. 3: 1 vol% methanol in water at 25 °C, for the example in Fig. 4: 1 vol% acetone in water at 25 °C.

[0077] The measurements were carried out at different ambient temperatures of 20°C (solid line), 25°C (dashed line) and 30°C (dash-dotted line).

[0078] The upper panel (A) shows the curve progression (peak determination) of the chemical compound of interest (methanol or acetone) without flow correction. From panels (A) it can be seen that the determination of the chemical compound occurs at very different times depending on the temperature, and that a maximum concentration can be detected at different times.

[0079] The lower panel B) shows the curve (peak determination) of the chemical compound of interest (methanol or acetone) with flow correction.

[0080] From panels B) of Figs. 3 and 4 it can be seen that the flow rate adjusted as a function of temperature results in a respective maximum of the concentration of the compound to be determined (methanol or acetone) occurring essentially at the same time or within a narrow time window.

[0081] It should be noted that the required flow rate correction is slightly different for methanol and acetone. The correction is not linear with the increase in temperature. It should also be noted that the corrections for other GC columns or separation columns would be different.

[0082] As already mentioned above, the required correction functions or correction quantities are stored in the control unit 24 and automatically applied to correct the signal.

[0083] In general, it can be observed that without flow rate correction (panels A of Fig. 3 and 4), the peaks of the analytes shift to later time points, are broader and their maximum is lower with decreasing column temperature.

[0084] The flow rate correction (panels B of Figs. 3 and 4) counteracts this so that all peaks recorded at different temperatures match.

[0085] In panels B) of Figures 3 and 4, the time of peak occurrence is indicated by an arrow, along with an indicated band within which the peaks occur. For Figure 3, the time can be identified at approximately 40 seconds, specifically within a range of approximately 37 to 43 seconds. For Figure 4, the time can be identified at approximately 60 seconds, specifically within a range of approximately 55 to 65 seconds.

[0086] The flow rates at temperatures of 20°C, 25°C, and 30°C shown in the figures, particularly in panel B, correspond to measured values, but may also assume different values ​​in other configurations. Despite the high analytical performance of gas chromatography in the selective measurement and quantification of target analytes (chemical compounds such as methanol or acetone in the examples above), this technology has so far been limited to analytical laboratories. One of the reasons for this is the need for precise control of the column temperature in a heated space, such as an oven. This required temperature control of GC columns limits miniaturization in terms of space, cost, and energy consumption.

[0087] With the proposed gas detection device 10 and the described method 500, a complex control of the column temperature can be dispensed with, whereby a reliable and reproducible determination of chemical compounds can be ensured by means of temperature detection and changing the flow rate as a function of a current (room) temperature through the separation column.

Claims

PATENT CLAIMS:

1. A gas detection device (10) configured to determine at least one chemical compound in a gaseous sample (gP), comprising a gas inlet (14) and a gas outlet (16); 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 gas detector (20) configured to quantify the at least one chemical compound after it has passed through the separation column (18), in particular to determine the concentration of the at least one chemical compound in the gaseous sample; at least one conveying device (22), in particular a pumping device, configured to actively convey the gaseous sample (gP) from the gas inlet (14) to the gas outlet (16) through the separation column (18);a control unit (24) which is designed to control the conveying device (22) at least one temperature sensor (26) which is designed to detect a state temperature in the region of the separation column (18) or in the separation column (18), characterized in that the control unit (24) is designed to control the conveying device (22) depending on the detected state temperature.; 2. Gas detection device (10) according to claim 1, characterized in that the control unit (24) is designed to adjust the conveying volume of the conveying device (22) as a function of the detected state temperature, such that the gaseous sample (gP) is conveyed from the gas inlet (14) to the gas outlet (16) at different state temperatures with different flow velocities.

3. Gas detection device (10) according to claim 1 or 2, characterized in that the control unit (24) is designed to control the conveying device (22) in such a way that the quantitative determination of the at least one chemical compound is present in each detection process of such a chemical compound after a predetermined, substantially constant period of time since the start of the detection process.

4. Gas detection device (10) according to claim 3, characterized in that the time period is approximately 10 to 600 seconds, in particular approximately 40 to 120 seconds.

5. Gas detection device (10) according to one of the preceding claims, characterized in that the state temperature is from -10°C to 50°C, in particular from 10°C to 35°C.

6. Gas detection device (10) according to one of the preceding claims, characterized in that it has at least one sensor (30) whose signal allows the delivery volume through the separation column (18) to be quantified.

7. Gas detection device (10) according to one of the preceding claims, characterized in that the chemical compound to be determined is methanol, ethanol, acetone, isoprene, formaldehyde, benzene, ammonia, acetic acid or hydrogen cyanide.

8. A method (500) for the quantitative determination of a chemical compound in a gaseous sample (gP), comprising the steps of: detecting (S501) a state temperature in the region or in a separation column (18); Determining (S502) a delivery volume as a function of the detected state temperature; Setting (S503) a conveying device (22) to the specific conveying volume and conveying the gaseous sample (gP) with the conveying volume through the separation column (18) from a gas inlet (14) to a gas outlet (16); Detection (S504) of the at least one chemical compound after a predetermined period of time, which remains substantially the same for each detection process of such a chemical compound, since the start of the detection process.

9. The method (500) according to claim 8, wherein it is carried out at a state temperature of -10°C to 50°C, in particular of 10°C to 35°C.

10. The method (500) according to claim 8 or 9, wherein it is carried out during the period of about 10 to 600 seconds, in particular about 40 to 120 seconds.

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