Gas chromatographic apparatus for measuring the concentration of volatile markers

Abstract

The present invention relates to a gas chromatography device 2 for measuring the concentration of a volatile marker. The device 2 comprises a first chromatographic column 8 and a first detector 12. It has been found that the retention times and peak heights of all compounds in a chromatogram are not universal constants of nature, but are strongly dependent on many parameters such as column dimensions, materials and operating conditions. By utilizing an additional detector 22 or an additional chromatographic column 24 (the additional detector 22 differing from the first detector 12 in detector characteristics and / or the additional chromatographic column 24 differing from the first chromatographic column 8 in column characteristics), these redundancies can be utilized to determine a reliable consensus concentration value for the marker and its confidence level can be determined.

Description

[Technical field]

[0001] The present invention relates to a gas chromatography apparatus, a method and a computer program for determining the concentration of a volatile marker. [Background technology]

[0002] A gas chromatography apparatus is a known device for detecting and determining the concentration of gaseous compounds. It consists of a chromatography column capable of separating a mixture of gases into its individual components, and a detector that outputs a signal depending on the concentration and / or type of gas passing through it.

[0003] Chromatography columns are limited in the number of gas compounds they can separate. Usually, this varies with the square root of the length of the column. This means that for shorter length columns, which are useful for so-called process gas chromatographs and even more so for micro gas chromatographs, the recorded chromatograms do not consist only of isolated peaks, but of a superposition of partially or completely overlapping peaks. This means that it can be difficult to identify the actual peak corresponding to the marker of interest and to determine the peak area of ​​the marker of interest, corrected for the overlapping contributions of neighboring peaks. This leads to inaccuracies and errors in the determination of the marker concentration. Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the present invention to provide a gas chromatography apparatus, method and computer program for more accurately determining the concentration of a volatile marker. [Means for solving the problem]

[0005] In a first aspect, a gas chromatography apparatus for determining the concentration of a volatile marker is presented, the apparatus having a sampling device, a first chromatography column, a process flow path connecting the sampling device to the chromatography column, and a first detector connected to the first chromatography column, the chromatography apparatus having at least one of an additional detector and an additional chromatography column, the additional detector differing from the first detector by a detector characteristic and / or the additional chromatography column differing from the first chromatography column by a column characteristic.

[0006] It has been found that the retention times and peak heights of all compounds in a chromatogram are not universal constants of nature, but are strongly dependent on many parameters such as column dimensions, materials and operating conditions. By combining concentration determinations from multiple non-identical chromatographic conditions, their redundancy can be exploited to determine a reliable consensus concentration value for the marker, and its confidence level can be determined.

[0007] In a preferred embodiment, the gas chromatography apparatus further comprises a sample flow path configured to direct the fluid to be sampled to the sampling device, and a valve device for connecting either the sample flow path or the process flow path to the sampling device, such that in the sampling mode the sampling device is connected to the sample flow path, and in the analysis mode the process flow path and the chromatography column are connected to the sampling device. The fluid may be either a gas or a liquid that is converted to a gas.

[0008] The gas sampling device is preferably configured as one of the following: a sample loop, a thermal desorber. Sample loops are widely available in commercial gas chromatography devices. It is recognized that a thermal desorber allows for the division of the adsorbed sample into multiple fractions that are injected into the column during successive chromatographic runs. In this way, a thermal desorber allows for the generation of multiple, particularly sequential, chromatographic conditions even when using a single sample, a single column, and a single detector.

[0009] The column characteristics can be at least one of the following: column dimensions, in particular column length, column diameter, column film thickness, column material, or a combination thereof; column operating conditions, in particular column temperature, column pressure, column flow rate, or a combination thereof. The underlying principle of this multiple column embodiment is to allow the generation of multiple chromatographic conditions with different peak patterns, such that the marker concentration can be determined independently from each condition. This allows for greater robustness and reliability of the final concentration estimate.

[0010] The detector characteristics can be at least one of the following: detector principle, sensing material, sensor operating conditions. Preferably, the first detector is connected in parallel or in series to the additional detector. In this regard, it is recognized that there is no detector that has universal sensitivity for all gas compounds, in the sense of a universal conversion factor of peak area to ppb concentration, independent of the gas compound. Thus, two non-identical detectors give different information, different peak heights for different compounds. Thus, even if the first detector already gives information that allows the determination of the marker concentration, there is an advantage to adding a second, especially non-identical, detector, since this adds different information. From the combination of these two detectors, a more reliable determination of the marker concentration can be obtained due to the combined information.

[0011] According to one embodiment, the first column is connected in parallel or in series to an additional column. The additional column can be connected to a first detector. The additional column can be connected to a second detector.

[0012] In another aspect of the invention, a method for determining the concentration of a volatile marker using gas chromatography is presented, the method including the steps of providing a first chromatogram under first chromatographic conditions, providing a second chromatogram under second chromatographic conditions, the second chromatographic conditions being different from the first chromatographic conditions, identifying a peak corresponding to the marker in each chromatogram, determining a peak area and / or peak height of the peak corresponding to the marker for each chromatogram, determining an estimate of the marker concentration based on the peak area and / or peak height for a known marker concentration using predetermined calibration information for each chromatogram, and determining a consensus value for the marker concentration from two estimates of the marker concentration from the two chromatograms.

[0013] In other words, for both chromatographic conditions, the markers of interest are fitted to expected peak positions taking into account the expected peak widths from their calibration chromatograms. From the comparison between the determined marker concentrations of both chromatograms, a robust estimation of the marker concentration and its confidence level can be made.

[0014] The first and second different chromatographic conditions can be established by utilizing a single sample and non-identical detectors for each chromatographic condition, preferably connected in parallel with each other or in series with each other.

[0015] The first and second different chromatographic conditions can be established by utilizing a single sample and non-identical columns for each chromatographic condition. Preferably, a separate detector is utilized for each non-identical column and / or a common detector is utilized for the two non-identical columns. The columns can be connected in parallel to each other or in series to each other.

[0016] In one embodiment, the first and second different chromatographic conditions are established by utilizing multiple sequential injections of a single sample, for example from a thermal desorber, and a chromatogram is determined for each sequential injection.

[0017] In a further embodiment, the first and second different chromatographic conditions are established by utilizing multiple sequential samples and different operating conditions, which can be characterized by at least one of the following: injection conditions, column flow rate, column pressure rate, column temperature, detector operating conditions, e.g., the temperature of a detection layer in a detector based on a chemiresistive detection principle.

[0018] Preferably, the identification of a peak corresponding to a marker is based on predetermined calibration information, hi one embodiment, the predetermined calibration information comprises a peak retention time and a peak conversion factor.

[0019] In this regard, the peak retention time is the time between the injection of the sample into the column and its maximum response measured at the detector. This retention time depends on the type of gas compound, polar / non-polar, boiling point, etc., the column material, e.g. polarity of the stationary phase, the column dimensions, the flow rate through the column and the column temperature, especially the dynamic temperature. The peak conversion factor h, especially the peak area per marker concentration, indicates the detector sensitivity of the detector for that particular marker.

[0020] Preferably, the predetermined calibration information further comprises at least one of: a peak width of a Gaussian standard deviation, a time constant of an exponential peak broadening.In one embodiment, the method includes determining a confidence level of the consensus value of the marker concentration.

[0021] Peak width is due to diffusional broadening in the column, which is typically proportional to the square root of the peak retention time. The exponential broadening time constant may be due to the gas volume inside the detector behaving as a continuous stirred tank reactor (CSTR), and therefore even if the marker enters as an ideal spike waveform, especially a Dirac spike waveform, the concentration in the detector volume follows an exponential decay with a time constant given by the detector volume divided by the volumetric flow rate. In practice, especially in short columns such as micro gas chromatographs, the exponential broadening time constant is significant compared to the Gaussian peak width.

[0022] In a further aspect of the invention, a gas chromatography apparatus is provided, comprising a providing unit configured to provide a first chromatogram under first chromatographic conditions and to provide a second chromatogram under second chromatographic conditions different from the first chromatographic conditions, and a processor configured to execute the steps of the method according to any of claims 6 to 13.

[0023] In yet another aspect, a computer program for determining the concentration of a marker in a sample is presented, the computer program comprising program code means for causing a computer to perform the steps of the method according to any of claims 6 to 13.

[0024] It is to be understood that the gas chromatography apparatus of claims 1 and 14, the method for determining the concentration of a volatile marker using gas chromatography of claim 6 and the computer program of claim 15 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0025] It is to be understood that a preferred embodiment of the invention can be any combination of the dependent claims or the above embodiments with the respective independent claim.

[0026] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0027] [Figure 1] 1A and 1B are schematic and exemplary diagrams illustrating embodiments of a gas chromatography apparatus for determining the concentration of a volatile marker; [Diagram 2] FIG. 2 shows a schematic and exemplary embodiment of a gas chromatography apparatus for determining the concentration of a volatile marker; [Diagram 3] FIG. 2 illustrates, in a schematic and exemplary manner, another embodiment of a gas chromatography apparatus in an alternative configuration. [Figure 4] FIG. 2 shows a schematic and exemplary embodiment of a gas chromatography apparatus for determining the concentration of a volatile marker; [Diagram 5] FIG. 1 illustrates another embodiment of a gas chromatography apparatus for determining the concentration of a volatile marker. [Figure 6] 1 illustrates yet another embodiment of a gas chromatography apparatus. [Figure 7] FIG. 1 illustrates a method for determining the concentration of a volatile marker using a gas chromatography device. [Figure 8] 1 illustrates another embodiment of a gas chromatography apparatus. [Figure 9] FIG. 2 shows sample chromatograms a to d obtained with multiple detectors, illustrating the method according to the present invention. [Figure 10] FIG. 2 shows sample chromatograms a to d obtained on multiple columns, illustrating the method according to the present invention. [Figure 11] FIG. 1 shows sample chromatograms a-d obtained with multiple injections illustrating the method according to the present invention. [Figure 12]FIG. 2 shows sample chromatograms a-d obtained on a number of samples illustrating the method according to the present invention. [Figure 13] 1 illustrates the method according to the invention. Alternative sample chromatograms a-d obtained on several samples are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] FIG. 1 exemplarily and diagrammatically shows a first embodiment of a gas chromatography device 2 for determining the concentration of a volatile marker. The gas chromatography device 2 allows the monitoring of continuous gas mixtures in industrial processes. The gas chromatography device 2 comprises a sampling device 4 configured as a sample loop 26. The sample loop 26 comprises a defined internal volume that can be switched between two modes with the aid of a valve device 14, namely a sampling mode and an analysis mode. In the sampling mode, the sample loop 26 is connected to a sample flow path 6. This is shown in FIG. 1 with the help of dotted lines. When the valve device 14 is switched to the analysis mode, the sample loop 26 is connected to a first chromatographic column 8. This is shown in FIG. 1 with the help of dashed lines. The gas chromatography device 2 is operated as follows:

[0029] The valve device 14 is initially switched to a sampling mode, meaning that the gas to be sampled is sent through the sample loop 26. After a sufficient time has elapsed for the composition of the gas in the sample loop 26 to be representative of the gas to be analyzed, the valve device 14 is switched to an analysis mode. By means of the pressure controller 18, the carrier gas provided by the carrier gas source 16 transports the gas sample in the sample loop 26 through the process flow path 10 into the first chromatographic column 8, where the gas sample is separated into gaseous compounds, particularly by interaction with the stationary phase of the column 8, which exit the column 8 at different times and are recorded by the first detector 12.

[0030] The first detector 12 provides a first chromatogram under first chromatographic conditions. The first detector 12 is connected to a second detector 22. The second detector 22 provides a second chromatogram under second chromatographic conditions. In other words, the first detector 12 and the second detector 22 output non-identical signals. The second detector 22 is connected to a gas outlet 20.

[0031] For example, the detectors 12, 22 can be selected from detectors of different types, such as photoionization, flame ionization, chemiresistive, amperometric, thermal conduction, capacitive, or, in the case of chemiresistive and amperometric detectors, from the same type but based on different materials, or from the same type and material but used under different conditions, e.g., two identical chemiresistive detectors used at different hotplate temperatures.

[0032] The first detector 12 and the second detector 22 are arranged in series. In the first embodiment, only a single sample, a single column 8, and a single chromatographic separation are required to generate a first chromatogram under first chromatographic conditions and a second chromatographic separation under second chromatographic conditions.

[0033] Figure 2 shows an alternative embodiment of a gas chromatography apparatus 2 similar to the embodiment shown in Figure 1. The main difference between the embodiments of Figures 1 and 2 is that the first detector 12 and the second detector 22 in Figure 2 are connected in parallel. And the first detector 12 and the second detector 22 differ with respect to detector characteristics such as detector type, materials utilized or operating conditions as described with reference to Figure 1. The first detector 12 and the second detector 22 are connected to a gas outlet 20.

[0034] 3 illustrates an alternative embodiment of a gas chromatography apparatus 2, in which the apparatus 2 includes at least two columns 8, 24, namely a first chromatographic column 8 and a second chromatographic column 24. In the embodiment of FIG. 3, the first chromatographic column 8 is connected in parallel with the second chromatographic column 24. The first chromatographic column 8 is connected to a first detector 12. The second chromatographic column 24 is connected to a second detector 22. The first detector 12 and the second detector 22 are connected to a gas outlet 20.

[0035] The underlying principle of the embodiment shown in FIG. 3 is to allow the creation of multiple chromatographic conditions with different peak patterns so that the marker concentration can be determined independently from each condition to allow for more robustness and confidence in the estimated final concentration, as will be explained with particular reference to FIG. 7.

[0036] FIG. 4 shows an alternative embodiment of a gas chromatography apparatus 2 utilizing multiple columns 8, 24. In the embodiment of FIG. 4, a first chromatographic column 8 is connected to a sample loop 26. Furthermore, the first chromatographic column 8 is connected to a first detector 12. The first detector 12 is connected to a second chromatographic column 24. The second chromatographic column 24 is connected to a second detector 22. The second detector 22 is connected to a gas outlet 20. In other words, compared to the embodiment of FIG. 3, the columns 8, 24 and the detectors 12, 22 are connected in series. In the embodiments of FIGS. 3 and 4, the first detector 12 is different from the second detector 22 and the first chromatographic column 8 is different from the second chromatographic column 24. The embodiment of FIG. 4 benefits from a higher detection limit since the sampled gas is not split into two streams and the complete sample volume is available to both detectors.

[0037] FIG. 5 shows another alternative multi-column embodiment including a first chromatographic column 8 and a second chromatographic column 24. Both chromatographic columns 8, 24 are connected to a common detector 12, which is in turn connected to a gas outlet 20. The columns 8, 24 can differ with respect to their column dimensions (particularly column length, column diameter or column film thickness), column material, or column operating conditions (particularly column temperature, column pressure or column flow rate). The main advantage of the embodiment of FIG. 5 is that the overall equipment costs are reduced, since only a single detector 12 is required. Different chromatographic conditions are generated by utilizing different sections of the chromatogram recorded by the common detector 12.

[0038] FIG. 6 shows an alternative embodiment of the gas chromatograph apparatus 2 in which a thermal desorber 28 is used instead of the sample loop 26 of FIGS. 1-5. When the valve device 14 is switched to a sampling mode (shown by the dotted line), the sample gas stream is sent through the thermal desorber 28. The thermal desorber 28 captures and stores a range of volatile compounds from the input gas stream when operating at ambient temperature. After sampling a desired amount of gas, the valve device 14, configured as a six-port valve, is switched to an analysis position shown by the dashed line. In the analysis position, carrier gas provided by the carrier gas source 16 is sent through the thermal desorber 28 towards the first chromatographic column 8. By rapidly heating the thermal desorber 28 to a certain set-point temperature, compounds previously absorbed during the sampling phase are desorbed and injected into the chromatographic column 8.

[0039] The range of volatile compounds that are desorbed depends on the actual set temperature. In general, volatile compounds with higher boiling points require higher temperatures to be desorbed from the sorbent than compounds with lower boiling points. It is recognized that the thermal desorber 28 allows for separation of the adsorbed sample into multiple fractions that are injected into the chromatography column 8 during sequential chromatographic runs.

[0040] In this way, the thermal desorber 28 makes it possible to generate multiple or sequential chromatographic conditions even using a single sample, a single column 8 and a single detector 12. The principle of operation of the device 2 disclosed in the embodiment of FIG. 6 is as follows:

[0041] The process begins with the transfer of the sample to the thermal desorber 28. A portion of the captured sample is then injected into the chromatographic column 8 under injection condition A, for example by heating the thermal desorber 28 to a temperature of 100° C., and the resulting chromatogram A is recorded by the detector 12. Then, under injection condition B, a further portion of the captured sample is injected into the column, for example by heating the thermal desorber 28 to a temperature of 150° C., and the resulting chromatogram B is recorded by the detector.

[0042] FIG. 7 shows an embodiment of a method 100 for determining the concentration of a volatile marker using gas chromatography. The method 100 includes steps 102 of providing a first chromatogram under a first chromatographic condition and 104 of providing a second chromatographic condition under a second chromatographic condition, the second chromatographic condition being different from the first chromatographic condition. The first chromatographic condition can be different from the second chromatographic condition by utilizing a single sample and non-identical detectors for each of the chromatographic conditions. Alternatively, the different chromatographic conditions can be established by utilizing a single sample and non-identical columns for each chromatographic condition. A separate detector can be utilized for each non-identical column, or a common detector can be utilized for the two non-identical columns.

[0043] Alternatively, the first and second different chromatographic conditions can be established by utilizing a single sample and multiple sequential injections, with a chromatogram being determined for each sequential injection. Alternatively, the first and second different chromatographic conditions can be established by utilizing multiple sequential samples and different operating conditions. The different operating conditions can be characterized by injection conditions, column flow rates, column pressure rates, column temperatures, or detector operating conditions (e.g., hotplate temperature for a chemiresistive sensor).

[0044] The method 100 further includes identifying 106 peaks corresponding to the markers in each chromatogram. The identification 106 of the peaks may be based on predefined calibration information. The predefined calibration information may include, for each of the chromatographic conditions, peak retention times, peak widths, in particular Gaussian standard deviation peak widths, and preferably exponential peak broadening time constants.

[0045] Method 100 further includes step 108 of determining a peak area and / or peak height of a peak associated with the marker in each chromatogram, and step 110 of determining an estimate of the marker concentration based on the peak areas and / or peak heights of known marker concentrations using the predetermined calibration information for each chromatogram. Method 100 further includes step 112 of determining a consensus value of the marker concentration from the two estimates of the marker concentration from the two chromatograms.

[0046] 8 shows an alternative embodiment of a chromatographic device 200. The chromatographic device 200 comprises a providing unit 202. The providing unit 202 is configured to provide a first chromatographic condition under a first chromatographic condition and to provide a second chromatographic condition under a second chromatographic condition, the second chromatographic condition being different from the first chromatographic condition.

[0047] The term "providing" should be understood to mean that the chromatogram is either determined with the help of the device itself or is provided to the device from an external source. The chromatography device 200 further comprises a processor 204. The processor 204 is configured to perform the steps of the method according to any of claims 6 to 13, in particular the steps of the method shown in FIG.

[0048] Figure 9 shows sample chromatograms a-d illustrating the method according to the invention for the embodiment shown in Figure 1. Panels a and b show chromatograms recorded with detectors A (left, detector 12 in Figure 1) and B (right, detector 22 in Figure 1) for a sample containing pure marker of interest (at a known concentration, in this case 1 molar ppb).

[0049] The resulting marker peaks recorded in chromatograms A and B are defined by four characteristics: - Peak retention time μ: the time from injection of the sample into the column to the maximum response measured by the detector. This retention time depends on the gas type (e.g. polar / non-polar), boiling point, column material (e.g. polarity of the stationary phase), column dimensions, flow rate through the column and column temperature (especially the dynamic temperature of the column). - Gaussian peak width σ: This is due to diffusional broadening within the column, which is typically proportional to the square root of the peak retention time. - Exponential broadening time constant τ: This arises from the gas volume inside the detector behaving as a continuous stirred tank reactor (CSTR), and even if the marker enters as an ideal (Dirac) spike, the concentration in the detector volume follows an exponential decay with a time constant τ given by the volume divided by the detector volume. In practice, especially for short columns, the exponential broadening time constant is significant compared to the Gaussian peak width σ. The peak conversion factor h, in particular the peak area per marker concentration, or alternatively the peak height per marker concentration, indicates the detector sensitivity of the detector for that particular marker.

[0050] Typically, when two non-identical detectors A and B are used, they will most likely have different sensitivities, possibly different time constants, and different retention times, but the Gaussian peak widths will typically be equal to each other.

[0051] The remaining two panels, c and d, of Figure 9 show chromatograms A and B obtained from a gas sample containing a mixture of components including the markers mentioned above. Panels c and d correspond to the same sample and the same column, but differ due to the unequal sensitivity between detectors A and B to the various components within the sample.

[0052] These are typical examples of chromatograms obtained with short column instruments, where compounds show at least partially overlapping peaks. The challenge is to determine the concentration of the marker of interest and therefore its contribution to the entire recorded chromatogram. By the way, most detectors have a linear output, which means that their output for a mixture is equal to the sum of the outputs that would result if all individual components were measured separately.

[0053] In this example, from the calibration chromatogram, the marker of interest is known to have a retention time of 6.1 minutes. The true concentration of the marker is 1.3 ppb.

[0054] Now, with respect to panels c and d, the fitting approach according to the invention is described. In the identification of the markers in the sample chromatogram, not only the expected retention time but also the expected Gaussian and exponential peak widths are taken into account. Thus, one attempts to fit the 6 min sample region with two exponentially spread Gaussian distributions, one of which has exactly the same peak parameters as the calibrated marker. The fitting shown in panel c contains a peak with exactly the expected retention time, Gaussian and exponential peak width from the calibration in a. Similarly, the fitting shown in panel d contains a peak identical to the calibration in b. Furthermore, the success of these two fittings can be concluded by comparing their resulting concentrations, which are in perfect agreement with 1.3 ppb.

[0055] Another strategy, which attempts to fit the peak around 6 minutes with a single exponentially spread Gaussian distribution, has proven inaccurate.

[0056] Figure 10 shows sample chromatograms obtained on different columns illustrating the method according to the invention. In the top panel, it can be seen that the column material affects both the retention time and the Gaussian peak width of the marker of interest. Thus, it is clear that the retention times, and relative elution order, of most compounds differ between column A and column B. This maximizes the chance that, by chance, the marker peak will be more isolated from the surrounding peaks if, under condition A, there is an overlapping peak masking the marker of interest, and if, under condition B, both the marker and the masking peak are shifted.

[0057] The method used in this embodiment is consistent with the general method of the present invention, where for both conditions, in this case in both columns, the markers of interest are fitted at the expected peak positions, taking into account the expected peak widths from their calibration chromatograms. From the comparison between the marker concentrations determined from both chromatograms, a robust estimation of the marker concentration and its confidence level can be made.

[0058] Figure 11 shows sample chromatograms a-d obtained from multiple injections illustrating the method according to the invention. The two left panels show the same markers and samples, specifically mixtures, used in the previous embodiment. In this reference example, the sample captured in the thermal desorber of Figure 6 is injected completely onto the column in a single injection event at a sufficiently high temperature.

[0059] In the remaining panels of FIG. 11, two injection conditions, A and B, are shown. Injection condition A is performed at low temperature, resulting in partial injection of compounds from the thermal desorber into the column. In the center bottom panel, it can be observed that, especially under the low temperature injection condition A, compounds with low retention times are desorbed, which are typically compounds with lower boiling points. Compounds with higher retention times, including the markers of interest, clearly remain inside the thermal desorber during injection A, but are then desorbed during the high temperature injection condition B. Note that some intermediate compounds are partially desorbed in condition A and partially desorbed in condition B.

[0060] According to the method of the present invention, before being used on a sample, the device requires calibration for the marker of interest. This means performing the exact chromatographic conditions on a sample consisting of pure marker of interest of known concentration. The calibration chromatograph obtained under injection conditions A and B is shown in the top right panel. Here, it can be seen that in this particular example, the marker of interest is not desorbed in condition A. The key in the final step of the method is to evaluate whether the separation of the marker between the two injections A and B in the measured sample matches the splitting during the calibration. This increases the confidence level of the determined concentration.

[0061] An additional advantage of this approach is that the total number of compounds per chromatographic run is reduced, allowing easier fitting of peaks. Optionally and beneficially, the column operating conditions corresponding to the successive injection conditions can be different, e.g., optimized for low boiling compounds resulting from injection A during the recording of chromatogram A, as well as for high boiling compounds during injection B. In that case, unlike the example of FIG. 11, the marker fittings in injections A and B do not need to share the same parameters for retention time and peak width. From the calibration at exactly the same column operating conditions, the marker parameters are known. In addition, according to the general method of the invention, they are used for fitting the marker peaks in the sample chromatograms.

[0062] 12 shows sample chromatograms obtained with multiple samples illustrating the method according to the present invention. In this embodiment, multiple non-identical chromatographic conditions are achieved by analyzing the samples sequentially under different conditions.

[0063] In known devices that can autonomously capture and analyze gas samples, for example indoor air in a greenhouse or animal barn, additional samples can be easily accessed. In addition, considering that for short columns, analysis times proceed within minutes, subsequent samples are likely to have approximately the same composition. The advantage of this embodiment is that it is cost-effective, since no duplicate elements are required in the device architecture, which means that a single column and a single detector are sufficient.

[0064] Ideally, two successive samples of the same composition should be analyzed under different conditions, e.g. different injection conditions A or B, and / or different column operating conditions A or B (including pressure / flow and temperature conditions), and / or different detector operating conditions A or B (including hotplate temperature settings in chemiresistive sensors).

[0065] Exemplary chromatograms for both cases are shown in Figure 12. The chromatograms are generated as follows: the method starts with transferring sample A to an injector, e.g. a thermal adsorbent. The sample is then injected into the column, and chromatographic conditions A are obtained. Immediately after sample A is injected into the column, and before all sample components have eluted from the column, a second sample B can be transferred again to the injector. Then, preferably once the column is empty again, a new injection can be made into the column, and chromatographic conditions B are obtained. The remaining steps are identical to the previous embodiment.

[0066] Ideally, samples A and B have equal composition. This is practically feasible since the two samples can be acquired without a long delay (the second sample B can already be transferred back to the injector before all components of sample A have been eluted from the column).

[0067] An example where the subsequent chromatographic conditions differ only in the injection conditions is shown in FIG. 12. The example in FIG. 12 is similar to the example in FIG. 11. In this example, the first sample A is fully injected onto the column (injection condition A). The subsequent sample B is split into two partial injections, injection B at a lower thermal desorption temperature and injection C at a higher temperature. This results in three chromatograms, for each of which the marker concentration can be determined and the consistency assessed based on the corresponding calibration measurements. In this example, if the fitted marker concentration of sample A is equal to the sum of the two fitted marker concentrations of sample B and furthermore the two fitted marker concentrations of sample B have relative values ​​consistent with the calibration, the confidence level for the determined concentration is high.

[0068] Another case is shown in FIG. 13, where successive chromatographic conditions have equal injections, but different chromatographic operating conditions such as column flow and temperature.

[0069] In this example, three consecutive samples A, B, C of the same composition are analyzed under three different column operating conditions. Each sample consists of three compounds: oxolane, cyclohexane, and dioxane. Condition A corresponds to a column linear velocity of 15 cm / s and a temperature of 50° C., which results in the lowest retention times for these three compounds. Condition B corresponds to a column linear velocity of 15 cm / s, but the column temperature is reduced to 30° C., which results in a higher spread between the retention times of the three compounds. Condition C corresponds to the default column temperature of 50° C., but the linear velocity is reduced to 7.5 cm / s, which results in an increase in the retention times of all three compounds.

[0070] In this example, cyclohexane is the marker of interest. Clearly, if the peak fit parameters for cyclohexane (in all three samples A, B, C) match those of the pure cyclohexane calibration, and most importantly, if the concentration values ​​for cyclohexane determined in all three consecutive samples A, B, C give the same concentration value, this gives a high degree of confidence in the consensus concentration value.

[0071] In this embodiment, successive samples are analyzed under purposely different conditions. This differs from the trivial case of replicate measurements, where successive samples are analyzed under identical conditions. An advantage of the inventive method disclosed herein is that it provides concentration values ​​with a higher degree of confidence than mere replication.

[0072] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0073] In the claims, the word "comprise" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality.

[0074] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0075] The steps such as providing a first chromatogram under first chromatographic conditions and providing a second chromatogram under second chromatographic conditions, or the above-mentioned identification or determination steps performed by one or several units or devices, can be performed by any other number of units or devices. These steps can be implemented as program code means of a computer program and / or as dedicated hardware.

[0076] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0077] Any reference signs in the claims should not be construed as limiting the scope.

[0078] The present invention relates to a gas chromatography device for measuring the concentration of a volatile marker. The device includes a first chromatographic column and a first detector. It has been found that the retention time and peak height of all compounds in a chromatogram are not natural universal constants, but are strongly dependent on many parameters such as column dimensions, materials and operating conditions. By utilizing an additional detector or an additional chromatographic column (the additional detector differs from the first detector in detector characteristics and / or the additional chromatographic column differs from the first chromatographic column in column characteristics), these redundancies can be utilized to determine a reliable consensus concentration value for the marker and its confidence level can be determined.

Claims

1. 1. A gas chromatography apparatus for measuring the concentration of a volatile marker, comprising: A sampling device; a first chromatography column; a process flow path connecting the sampling device to the first chromatography column; a first detector connected to the first chromatography column; and the gas chromatography device further comprises: additional detectors, additional chromatography columns, and A gas chromatography apparatus, wherein the additional detector differs from the first detector in detector characteristics and / or the additional chromatography column differs from the first chromatography column in column characteristics.

2. a sample flow path configured to guide a fluid to be sampled to the sampling device; a valve device for connecting either the sample flow path or the process flow path to the sampling device; and 2. The gas chromatography system of claim 1, wherein in a sampling mode, the sampling device is connected to the sample flow path, and in an analysis mode, the process flow path and the chromatography column are connected to the sampling device.

3. 3. The gas chromatography apparatus of claim 1, wherein the sampling device is configured as one of a sample loop and a thermal desorber.

4. The column characteristics are: Column dimensions, Column materials, column operating conditions, 3. The gas chromatography apparatus according to claim 1, wherein the gas chromatography apparatus is at least one of the following:

5. The detector characteristic is Detector principle, Sensing materials, Sensor operating conditions, 3. The gas chromatography apparatus according to claim 1, wherein the gas chromatography apparatus is at least one of the following:

6. 1. A method for measuring the concentration of a volatile marker using gas chromatography, comprising: providing a first chromatogram under first chromatographic conditions; providing a second chromatogram under second chromatographic conditions, the second chromatographic conditions being different from the first chromatographic conditions; identifying peaks in each chromatogram corresponding to the markers; determining the peak area and / or peak height of the peak corresponding to the marker in each chromatogram; determining an estimate of the marker concentration based on peak area and / or peak height for known marker concentrations using predetermined calibration information in each chromatogram; determining a consensus value for the marker concentration from the two estimates of the marker concentration from the two chromatograms; A method having the following.

7. 7. The method of claim 6, wherein the different first and second chromatographic conditions are established by utilizing a single sample and multiple sequential injections, and a chromatogram is determined for each sequential injection.

8. 7. The method of claim 6, wherein the different first and second chromatographic conditions are established by utilizing multiple sequential samples and different operating conditions.

9. The different operating conditions are: injection conditions, column flow rate, column pressure rate, column temperature, detector temperature, 9. The method of claim 8, characterized by at least one of:

10. 10. The method of claim 6, wherein the identification of peaks corresponding to markers is based on predetermined calibration information.

11. 10. The method of claim 6, wherein the predetermined calibration information comprises a peak retention time and a peak conversion factor.

12. The predetermined calibration information is Gaussian standard deviation peak width, the time constant of the exponential peak broadening, The method of claim 11 , further comprising at least one of:

13. 10. The method of claim 6, further comprising determining a confidence level for the consensus value of the marker concentration.

14. a providing unit configured to provide a first chromatogram under first chromatographic conditions and to provide a second chromatogram under second chromatographic conditions different from the first chromatographic conditions; A processor configured to perform the method of any one of claims 6 to 9; A gas chromatography apparatus having:

15. A computer program for determining the concentration of a marker in a sample, the computer program being executed by a computer and causing the computer to carry out the method of any one of claims 6 to 9.

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