Volatile pfas-fvc analysis system and method

Abstract

The primary trap concentrates the sample, then volatile, more so than CO2, retained compounds are flushed forward to the secondary trap. In some embodiments, the primary trap is isolated from the secondary trap prior to CO2 elution, and the pressure in the primary trap is reduced to below atmospheric pressure. At this point, a pressure sensor measures the expansion of the CO2 into the vacuum reservoir to determine the amount of CO2, and the CO2 is removed. Optionally, an inert gas is used to eliminate any residual CO2, either under positive pressure to replace the removal of CO2 under vacuum, or as an optional additional step after the CO2 is removed under vacuum. After the CO2 is removed, the primary trap is heated, and is back-flushed to the secondary trap, which is then pre-heated, and either injected directly into the GCMS, or further condensed using an open-tubular focusing trap to enable faster injection rates into the GCMS.

Description

Cross-reference to related applications

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 623,759, filed January 22, 2024, the entire disclosure of which is incorporated herein by reference for all purposes. Technical Field

[0002] This disclosure generally relates to sample preparation for GCMS analysis, and more specifically to the removal of carbon dioxide (CO2) from a sample while recovering compounds that are more volatile than CO2 and compounds that are less volatile than CO2. Background Technology

[0003] Pre-concentration systems for preparing trace-level samples for gas chromatography (GC) or gas chromatography-mass spectrometry (GCMS) analysis have existed for decades to enrich compounds of interest in large gaseous samples, allowing GC detectors to detect these compounds at levels far below what is achievable without pre-concentration. Most GC / GCMS currently uses capillary GC columns, with flow rates typically ranging from 0.5 cc / min to 2 cc / min. Typical peak widths in capillary GC runs are 3 to 6 seconds. Therefore, the optimal injection time must be approximately 6 seconds or less. At a flow rate of 1 cc / min, a 6-second injection requires limiting the sample volume to 0.1 cc or less. However, typically, sub-PPB level detection by GCMS requires a sample volume of 100 cc or more. Therefore, samples ranging from 100 cc to 500 cc must be reduced to 0.1 cc or less before injection, which in this example could provide 1000-fold to 5000-fold enrichment. Typically, enrichment of the target compound means eliminating unimportant compounds and / or compounds that might hinder the ability to reduce the sample volume to 0.1 cc or degrade the performance of GC / GCMS. In most applications, a solution for eliminating atmospheric matrix components without loss of the target compound can be found by finding a combination of sorbents (adsorbents) that, when operated at specific temperatures, allow the removal of N2, O2, Ar, and CO2 without loss of the target compound. The final matrix component (water) can be removed by using one of many dehydration techniques (cold dehydration traps, chemical dehydration traps, etc.), or by first condensing all the target compound, including water, and then purging the target compound onto a secondary trap while allowing most of the water to condense in the first stage. This approach is effective because during trace chemical analysis, the concentration of water is often millions of times higher than that of the compound of interest. Therefore, a post-water knockout purge volume can be selected to return all the compound of interest to the gas phase while being far from sufficient to evaporate all the condensate, thus successfully eliminating excess water and its impact on the analysis.

[0004] While N2, O2, and Ar can be removed via cold adsorbent beds with almost no loss of the compounds of interest, carbon dioxide (CO2) has always presented challenges in analyzing many low-boiling-point compounds. CO2 has a triple point of -78°C, at which it can exist as a solid, liquid, or gas. Some greenhouse gases and perfluoroalkyl substances (PFAS) have boiling points even below this temperature, and many of these compounds cannot be captured and retained on any known adsorbent at any temperature that allows CO2 removal during pre-concentration processes. Various pre-concentration systems used to measure greenhouse gases at sub-parts-per-trillion (sub-ppt) levels actually measure not only CO2 concentrations but also many fluorinated and chlorinated compounds, but these systems employ multiple columns and non-MS detectors, as well as PLOT or even packed columns, to handle CO2 in relatively higher concentrations compared to other trace gases. There is a need for a system capable of analyzing compounds with retention rates below and above CO2 on a cold adsorbent trap, while removing CO2 before injecting the extracted sample into a single-column GC or GCMS system, even at CO2 levels as high as 4% (40,000 PPM), such as when measuring flue gas plumes.

[0005] The US EPA method OTM-50, introduced at the end of 2023, contains 30 compounds, which are either PFAS (perfluoroalkyl substances) or VFCs (volatile fluorinated compounds) with boiling points ranging from -128°C (CF4) to approximately 100°C. OTM-50 is a flue gas sampling method where the CO2 level in the final collected gas phase sample is expected to be 0.5% to 4%. No combination of adsorbents has been found capable of both retaining CF4 and allowing CO2 to pass through at any temperature; therefore, the initial draft release of method OTM-50 required two separate analyses. The first analysis was used to quantify CF4, where CO2 was not removed initially, while the second analysis was used for all less volatile compounds, allowing CO2 to be removed from the trapping medium without loss of these compounds. Using a GC column selected for OTM-50, CF4 elutes before a very large CO2 peak, so CO2 does not interfere with the CF4 response, thus eliminating the need to remove CO2 when only CF4 is to be analyzed. However, the initial release of OTM-50 was limited to a volume of 20 cc due to various factors, resulting in less co-injected CO2 than the initially expected 200 cc, thus leading to a suboptimal CF4 response. When analyzing the remaining compounds on the OTM-50 list using the expected 200 cc sample volume, CO2 had to be removed. This was because expansion prevented the achievement of the optimal injection volume of 0.1 cc, and co-elution with some target compounds resulted in signal loss of up to 100% in the detector (mass spectrometer). Summary of the Invention

[0006] This disclosure generally relates to sample preparation for GCMS analysis, and more specifically to the removal of carbon dioxide (CO2) from a sample while recovering compounds more volatile than CO2 and less volatile than CO2. A primary cold adsorbent trap concentrates the sample, followed by forward flushing of retained compounds more volatile than CO2 to a secondary cold adsorbent trap. Forward flushing to the secondary trap is stopped before CO2 elution, and the primary trap is isolated from the secondary trap. The system then removes CO2 using one of two possible pathways. In one pathway, the primary trap is placed under vacuum and warmed while monitoring the expansion of CO2 from the primary trap, thereby using the total pressure increase to measure the amount of CO2 present without removing CO2 from the primary trap using a flushing gas. In another pathway, the system warms the primary trap while isolating it from the secondary trap to purge CO2 from the primary trap without placing the primary trap under vacuum. In some embodiments, the first approach to removing CO2 from the first trap under vacuum further includes: using a small amount of inert gas, if necessary, to eliminate interference from CO2 on the analysis of other collected compounds. After CO2 removal, the primary trap is heated and backflushed to a secondary trap, which is then preheated and either directly injected into the GCMS or further condensed using an open-tube focusing trap to achieve a faster injection rate into the GCMS. Attached Figure Description

[0007] Figure 1 An example system for removing CO2 from a chemical sample prior to chemical analysis is illustrated according to some embodiments of the present disclosure.

[0008] Figure 2 The illustration shows an example process for removing CO2 from a chemical sample prior to chemical analysis, according to some embodiments of the present disclosure.

[0009] Figures 3A to 3G The illustration shows flow paths facilitated by valves(s) during process steps according to some embodiments of the present disclosure. Detailed Implementation

[0010] In the following description, reference is made to the accompanying drawings, which form a part of the description, and specific examples in which they may be practiced are illustrated by illustration. It should be understood that other examples may be used and other changes may be made without departing from the scope of the examples in this disclosure.

[0011] This disclosure generally relates to sample preparation for GCMS analysis, and more specifically to the removal of carbon dioxide (CO2) from a sample while recovering compounds more volatile than CO2 and less volatile than CO2. A primary cold adsorbent trap concentrates the sample, followed by forward flushing of retained compounds more volatile than CO2 to a secondary cold adsorbent trap. Forward flushing to the secondary trap is stopped before CO2 elution, and the primary trap is isolated from the secondary trap. The system then removes CO2 using one of two possible pathways. In one pathway, the primary trap is placed under vacuum and warmed while monitoring the expansion of CO2 from the primary trap, thereby using the total pressure increase to measure the amount of CO2 present without removing CO2 from the primary trap using a flushing gas. In another pathway, the system warms the primary trap while isolating it from the secondary trap to purge CO2 from the primary trap without placing the primary trap under vacuum. In some embodiments, the first approach to removing CO2 from the first trap under vacuum further includes: using a small amount of inert gas, if necessary, to eliminate interference from CO2 on the analysis of other collected compounds. After CO2 removal, the primary trap is heated and backflushed to a secondary trap, which is then preheated and either directly injected into the GCMS or further condensed using an open-tube focusing trap to achieve a faster injection rate into the GCMS.

[0012] Figure 1 An example system for removing CO2 from a chemical sample prior to chemical analysis, according to some embodiments of the present disclosure, is illustrated. Figure 1 As shown, the system includes a primary trap 110, a secondary trap 120, a vacuum reservoir 150, a vacuum sensor 151, a vacuum pump 152, a gas chromatograph (GC) 160, and one or more valves 140. Optionally, the system 100 also includes a focusing trap 130. See below for reference. Figure 2 The operation of system 100 is described in more detail in Figure 3.

[0013] In some embodiments, valve(s) 140 include one or more rotary valves. Other suitable valves are also possible. Valve(s) 140 are connected to primary trap 110, secondary trap 120, vacuum reservoir 150, vacuum sensor 151, vacuum pump 152, GC 160, and focusing trap 130 (in a system including focusing trap 130). Opening, closing, and / or otherwise altering the configuration of valve(s) 140 changes the flow path through system 100, including changing which components are connected together, the direction of flow through components, and / or stopping flow through one or more components. For example, valve(s) 140 facilitate Figures 3A to 3GThe primary trap 110, secondary trap 120 and optional focusing trap 130 are shown in the diagram in their flow and non-flow states.

[0014] The (multiple) valves 140 include inlet control valves used to select one of a plurality of possible positions to allow different gas flows into system 100. These gas flows may include inert gases, internal standards, calibration standards, and / or (multiple) gas samples. Optionally, the inlet control valves include multiple inlets connected to samples and are compatible with automated sample injectors for automatic sample connection to enable unattended analysis in production laboratories.

[0015] During the trapping process, internal standards can be added to the trap to allow the detector sensitivity to be determined at analysis time. That is, the absolute sensitivity of some detectors, such as mass spectrometers, can fluctuate, so the injection of a known amount of internal standard during any given analysis allows the absolute sensitivity of the mass spectrometer to be correlated with the response of the internal standard, creating a “relative response” that is used to obtain a more accurate analysis of the true sample in which the concentration of the target compound in the sample to be determined is. In other words, if the response of the internal standard decreases by 10%, the response of the target compound is expected to decrease by 10%, so this decrease does not lead to an error in the measurement of the target compound. Calibration standards are mixtures of target compounds at known concentrations. These mixtures allow the determination of the MS response factor of each compound relative to the internal standard compounds, so that the peak area in the GCMS analysis can be correlated with a given compound concentration. They are also used to check the linearity of the method, evaluate the dynamic range of the technique, and determine the detection limit of the method. These calibration standards are typically run at least once a day to ensure that the change in the response of the target compound relative to the internal standard does not exceed approximately ±30%.

[0016] The primary trap 110 is a cold trap comprising one or more adsorbent beds. System 100 also includes a dehydration zone 112, a cryogenic valve 114, and a heater 116 adjacent to the primary trap 110. For example, the cryogenic valve 114 can cool the temperature of the primary trap 110 to a range of -80°C to -150°C during trapping. The cryogenic temperature of the primary trap 110 results in the temperature of the dehydration zone 112 also being within this range, and the close proximity of the dehydration trap 112 allows the dehydration zone 112 to be controlled within a range of 0°C to -30°C, limiting the amount of water that can enter or exit the primary trap without being removed as solid water (H2O(s)) or ice. The primary trap 110 traps samples including compounds less volatile than CO2, compounds more volatile than CO2, and CO2. After the sample is captured, valve 140 promotes forward flow through primary trap 110 to transfer compounds less volatile than CO2 from primary trap 110 to secondary trap 120 in the forward flow direction.

[0017] The primary trap 110 is configured to allow compounds more volatile than CO2 to be eluted through the primary trap 110 to the secondary trap 120, and to retain compounds less volatile than CO2 during CO2 removal using one of the two pathways further described in detail herein. In one pathway, the primary trap 110 is placed under vacuum and warmed while monitoring the expansion of CO2 from the primary trap 110, thereby using the total pressure increase to measure the amount of CO2 present without removing CO2 from the primary trap using a purging gas. Optionally, a small amount of inert gas may be used after the first pathway, if necessary, to eliminate interference from CO2 on the analysis of other collected compounds. In another pathway, the system warms the primary trap while isolating it from the secondary trap to purge CO2 from the primary trap without placing the primary trap under vacuum. To minimize water transfer to GC 160 and avoid water-induced interference, the dewatering trap 112 is maintained at a temperature range of 0°C to -30°C while the sample is transferred from the primary trap 110 to the secondary trap 120, thus allowing only sample flow with a dew point between 0°C and -30°C. During this time, the primary trap 110 is heated to a temperature range of 100°C to 200°C using heater 116 to release sample compounds. As the compounds are transferred from the primary trap 110 to the secondary trap 120 via valve 140, the low temperature of the dewatering zone 112 may cause water to condense and remain in the dewatering zone 112 instead of advancing to the secondary trap 120, thereby removing water from the remainder of the sample prior to analysis.

[0018] Vacuum reservoir 150 and vacuum sensor 151 can be connected together to measure the volume during trapping by sensing pressure changes in vacuum reservoir 150. For example, if the volume of vacuum reservoir 150 is 600 cc, a change of 1 / 3 atmospheres in pressure might require 1 / 3 × 600 cc = 200 cc of volume to pass through primary trap 110 and enter vacuum reservoir 150. Similarly, the system can monitor sample volume during other steps of the sample preparation process based on pressure changes in vacuum reservoir 150 measured using vacuum sensor 151. When primary trap 110 is heated to a point where CO2 becomes desorbable, vacuum sensor 151 can measure an increase in pressure in vacuum reservoir 150 that is proportional to the amount of CO2 collected in the trap. This increase can be used to increase the volume recovered in vacuum reservoir 150 that was condensed in primary trap 110 during the initial sample trapping. Unlike other approaches that cannot estimate the amount of CO2 in a sample, knowing the approximate concentration of CO2 in the sample, ranging from 0.1% to 4%, can add value to the analysis. Furthermore, using CO2 as its own purge gas has a major advantage when capturing large amounts of CO2. During the initial purge of compounds lighter and / or more volatile than CO2 into the secondary trap, CO2 moves deeper into the trap compared to where it was initially captured, and is partially separated from the less volatile compounds remaining in the primary trap. Therefore, during the expansion of up to 8 cc of CO2 from the primary trap in the forward flow direction, the less volatile compounds that have not yet penetrated into the trap experience almost no flow volume in the forward direction, meaning they have no reason to move forward with the expanding CO2 and leave the primary trap. Thus, large amounts of CO2 can be captured and removed without losing the slightly less volatile compounds of interest in the primary trap.

[0019] Vacuum pump 152 can be used to evacuate the entire system 100 or only in vacuum reservoir 150. When evacuating the entire system 100, the temperature of primary trap 110 needs to be low enough to retain CO2 to allow for later measurement of the amount of CO2. Connecting vacuum pump 152 to the inlet control valve allows for purging and flushing of the inlet control valve. Therefore, vacuum pump 152 can be switchably coupled to vacuum reservoir 150, coupled to the entire system 100, or disconnected.

[0020] During CO2 removal, the system 100 can be brought under vacuum by opening one or more valves connecting the vacuum pump 152 to other components of the system 100, such as the primary trap 110. At this time, valve(s) 140 connecting various gas sources to the inlets of the system 100 are closed. Thus, the only gas flow is expanding CO2, which extends beyond the point where less volatile compounds are deposited on the primary trap. This significantly reduces the likelihood of loss of other compounds on the primary trap 110 compared to removing CO2 using a strict flushing technique, by using less purge gas. Furthermore, this approach results in a more consistent level of residual CO2 to be purged from the primary trap 110, regardless of whether the original sample contains 0.1% or 4% CO2.

[0021] Secondary trap 120 is a cold trap with an inner diameter smaller than that of primary trap 110, to allow for faster injection into GC 160 after desorption by secondary trap 120. For example, the inner diameter of primary trap 110 may be 2 mm to 2.5 mm, and the inner diameter of secondary trap 120 may be 1 mm. System 100 also includes a cryogenic valve 124 and a heater 126 adjacent to secondary trap 120. Secondary trap 120 is kept cryogenic during the transfer of compound from primary trap 110 to secondary trap and is heated (e.g., using heater 126) during the transfer of compound from secondary trap 120 to GC 160 (optionally, via focusing trap 130), as referenced. Figure 2 As further described in detail in Figure 3.

[0022] Some embodiments include a focusing trap 130. The focusing trap 130 is an open tubular column that can operate at near liquid nitrogen temperatures. After CO2 removal and before analysis by GC 160, the focusing trap 130 reduces the sample volume.

[0023] In some embodiments, valve 140 connects focusing trap 130 between secondary trap 120 and GC 160, wherein the sample moves in a forward direction through focusing trap 130. In other words, the sample enters from secondary trap 120 at a first end of focusing trap 130 and exits from a second end of focusing trap 130, different from the first end, to be transferred to GC 160 for analysis.

[0024] Figure 2 An example process 200 for removing CO2 from a chemical sample prior to chemical analysis, according to some embodiments of the present disclosure, is illustrated. (See above reference) Figure 1 Described and referenced Figure 2The system 100, further detailed in Figure 3, performs process 200. Process 200 pre-concentrates a sample containing a range of very light to heavy chemicals in the presence of CO2, and removes some to most of the CO2. For optimal results when analyzing the remaining compounds by capillary GC or GCMS, CO2 must be removed from the sample. As an example, the sample may include CF4, a compound whose retention on almost all adsorbates is weaker than CO2 at any temperature and must be captured while removing most of the CO2. Samples prepared according to the examples herein may also include methane, xenon, krypton, NF3, and other chemicals that are less likely to be retained by the trap than CO2. In some embodiments, process 200 is performed in the order of the steps described herein. In some embodiments, process 200 is performed in a different order. In some variations of process 200, steps may be repeated or skipped without departing from the scope of this disclosure.

[0025] Figures 3A to 3G The illustration shows flow paths facilitated by valve(s) 140 during steps of process 200 according to some embodiments of the present disclosure. Valve(s) 140 control gas flow into and out of the primary trap 110 and the secondary trap 120.

[0026] In step 201, the primary trap 110 is used to trap all compounds while allowing nitrogen, oxygen, and argon to pass through the primary trap 110 without being retained. During step 201, valve 140 allows the sample to flow through the primary trap 110 in a first direction, such as... Figure 3A As shown. The sample enters the first end of the primary trap 110, and the lightest compounds exit the primary trap 110 through the second end. These permanent gases have boiling points between -180°C and -196°C, and, for example, when using a suitable adsorbent, can be easily removed from the system 100 while trapping other compounds with boiling points above -160°C. The primary trap 110 is cooled to a sufficiently low temperature to allow all target compounds to be retained by the primary trap 110. During this time, the secondary trap 120 and the optional focusing trap 130 (if used) are not connected to the primary trap 110. For example, during trapping, a cryogenic valve 114 cools the primary trap 110 to a temperature in the range of -120°C to -150°C. During step 201, since the secondary trap 120 and the optional focusing trap 130 are not in the flow path during the initial sample trapping, the secondary trap 120 and the optional focusing trap 130 are not temperature controlled.

[0027] Typically, the strength of the adsorbent can increase up to 10-fold for every 35°C decrease in temperature, with experimentally verified variations in trapping strength. Therefore, one or more adsorbents are used in the primary trap 110 such that, when operating at reduced temperatures (e.g., -20°C to -160°C), the primary trap 110 is strong enough to prevent even the lightest target compound from penetrating it at the maximum trapping volume required to reach the desired detection limit (e.g., 200 cc for 0.001 PPB using SIM or SRM mode (EI-MSMS)). The gas volume passing through the primary trap 110 can be determined by: using a mass flow controller and time integration; using a fixed flow limiter (if both inlet and outlet pressures are constant); or using a vacuum reservoir 150 and the ideal gas law PV=nRT to determine the amount of gas that has passed through the primary trap 110. When the volume of gas passing through the primary trap 110 is measured using a mass flow controller, process 200 includes a standard purge, rather than a vacuum purge, to remove CO2. After trapping, an inert gas (such as helium or hydrogen) that is also used as a GC carrier gas can be passed through the primary trap 110 to remove any remaining N2, O2, and Ar that may not have been removed from the primary trap 110.

[0028] In some approaches, system 100 uses a mass flow controller to measure the purge gas and sample entering the primary trap 110. Using a mass flow controller in this manner can increase the chance of carryover between samples, especially when analyzing high-concentration samples, as the sample flows through the mass flow controller. If a high-concentration sample is encountered, adsorption or transfer to the dead volume within the MFC may occur, resulting in carryover in subsequent analyses. As described in more detail below, in some embodiments, system 100 uses a vacuum reservoir 150 to measure CO2, thereby avoiding this problem.

[0029] In step 202, the temperature of the primary trap 110 may be increased to allow compounds more volatile than CO2 to be completely purged through the primary trap 110 for delivery to the secondary trap 120. The secondary trap 120, through a combination of adsorbent strength and low temperature, is capable of retaining light-eluting compounds, such as CF4 (boiling point = -127°C), NF3 (boiling point = -128°C), one of the other examples mentioned above, and / or other compounds of interest more volatile than CO2 in the analysis. That is, in this case, the primary trap 110 is used as a packing GC column to separate highly volatile compounds from less volatile compounds, thereby allowing the highly volatile compounds to elute from the primary trap 110, which acts as a packing GC column, and then be captured on the secondary trap 120. During step 202, valves 140 control the flow of the sample from the primary trap 110 to the secondary trap 120, such as... Figure 3B As shown. The primary trap 110 is forward flushed; in step 202, compounds exit the primary trap 110 from an end in the same direction as the flow direction of the compounds in step 201, different from the end into the primary trap 110 in step 201. During step 202, a cryogenic valve 114 controls the temperature of the primary trap 110 to be set too low to elute CO2 (and compounds of interest less volatile than CO2) but high enough to allow highly volatile compounds of interest (e.g., CF4 and / or NF3) to purge through the primary trap 110, such as temperatures in the range of -30°C to -110°C, depending on the adsorbent used in the primary trap 110. However, during step 202, CO2 can move deeper into the primary trap 110 compared to less volatile compounds, thus allowing CO2 to potentially expand forward, while compounds less volatile than CO2 will experience very little forward flow because they are now “behind” the CO2 in the primary trap 110 relative to the forward flow direction, and therefore have a very small chance of being lost through the forward flow direction.

[0030] In some embodiments, after step 202, the method proceeds to step 206 to purge CO2 while the primary trap 110 is under positive pressure. In other embodiments described below, the method includes steps 203 and / or 204 between steps 202 and 206 for removing CO2 using a vacuum. In some embodiments that do not include steps 203 and 204, after step 202, the method includes: changing the flow path to disconnect the series communication between the secondary trap 120 and the primary trap 110, and then proceeding to step 206. In step 206, heater 116 warms the primary trap 110 to a temperature that allows CO2 to be purgeed forward from the primary trap 110 while the system 100 purges CO2 without loss of residual compounds. This method is suitable for samples that do not contain compounds light enough to be lost during CO2 purging from the primary trap 110 and / or samples that contain relatively low concentrations of CO2. For samples containing one or more additional compounds that may be eluted during CO2 removal, or when there are higher levels (0.2%, 4% or higher) of CO2, additional steps 203 and / or 204 may be used, as now explained.

[0031] In step 203, the primary trap 110 is again isolated from the secondary trap 120, and a vacuum pump 152 is used to evacuate the primary trap 110 (and the portion of system 100 fluidly coupled to the primary trap 110), after which the vacuum pump 152 is isolated from system 100 and the primary trap 110. At this point, the inlet of system 100 must be closed to allow the vacuum to form. During step 203, valves 140 stop flow through the primary trap 110 and disconnect the primary trap 110 from the secondary trap 120, as... Figure 3C As shown. Multiple valves 140 connect the primary trap 110 to a vacuum reservoir 150, which is connected to a vacuum pump 152. Because the secondary trap 120 is not connected in series with the primary trap 110 during step 203, the secondary trap 120 is not emptied during step 203.

[0032] In step 204, the primary trap 110 is heated to a point where CO2 becomes desorbable on the primary trap 110. Because the volume of CO2 contained in the primary trap 110 is large relative to all other trace level compounds, the expansion of samples containing 0.2% to 4% CO2 can be measured using the vacuum sensor 151 and the vacuum reservoir 150. For samples containing less than 0.2% CO2, such as when analyzing ambient or indoor air quality, steps 203 and 204 can be skipped. During step 204, valve(s) 140 open both ends of the primary trap 110 and isolate the primary trap 110 from the secondary trap 120, as... Figure 3A As shown, the flow is guided through the primary trap 110 into the vacuum reservoir. Therefore, the direction of flow through the primary trap 110 during step 204 is the same as the flow direction during step 201. During step 204, the primary trap 110 is connected to the vacuum reservoir 150.

[0033] If a mass flow controller (MFC) is used to measure the sample volume during step 201, with the MFC located before the primary trap 110, CO2 will be added to the total measurement with a slight error, as CO2 has a 30% difference in response to MFCs calibrated for air or nitrogen. However, if the MFC or vacuum reservoir 150 used to measure the collected volume is downstream of the primary trap 110, CO2 will be removed in the primary trap 110 and will not be added to the total volume measured downstream, which could result in an error of up to 4% when CO2 constitutes 4% of the sample. However, by measuring the expansion of CO2 and knowing the volume of the trapping system 100, this volume can be taken into account when making calculations. Therefore, if a volume of 8 cc is recorded using the vacuum reservoir 150 technique in step 201, and then the pressure increases by 0.2 psi during the expansion of CO2 to a volume of 600 cc in the vacuum reservoir 150, the actual volume captured in step 201 could be 208 cc, and this volume can be used during data processing to eliminate the 4% error that would otherwise be present. The vacuum sensor 151 coupled to the vacuum reservoir 150 can measure pressure changes within + / - 0.01 psia, thus allowing the system 100 to measure CO2 in samples containing 0.2% to 4% CO2.

[0034] Furthermore, using this vacuum expansion approach to remove CO2 from the primary trap 110 has another advantage. Typically, the amount of flushing gas required to remove 8 cc of CO2 from the primary trap may be 30 cc to 50 cc or more, at which point it may be difficult to retain other light compounds with volatility almost equivalent to CO2 on the trap. However, since CO2 is even more volatile than compounds with the next lower volatility, CO2 has already migrated to a deeper part of the primary trap during the initial trapping and when one or more of the lightest compounds (e.g., CF4, methane) are purged forward into the secondary trap. This means that most of the expansion will not push the lighter compounds in the direction of the trap outlet, and therefore the movement of these lighter compounds in that direction should be minimal, thus greatly reducing the likelihood of their loss during the CO2 removal step.

[0035] In step 206, a small amount of purge gas (e.g., ultra-high purity N2 or He) may be used to remove any residual CO2 remaining in the primary trap 110. Once CO2 expansion is complete during step 204, the residual amount of CO2 should be fairly consistent between samples. During step 206, valves 140 isolate the secondary trap 120 and facilitate flow through the primary trap 110, as... Figure 3A As shown. During step 206, the direction of flow through the primary trap 110 is the same as the direction of flow into the primary trap 110 during step 201; the compound exits the primary trap 110 through an opening in step 206, the same opening through which the compound exited the primary trap 110 during step 201. In some embodiments, such as in an implementation including steps 203 and / or 204, the primary trap 110 is under vacuum when step 206 occurs. In some embodiments, such as in an implementation including steps 203 and / or 204, the primary trap 110 is under positive pressure when step 206 occurs. During step 206, the primary trap may optionally be at a temperature in the range of -20°C to -80°C.

[0036] In step 207, by optionally preheating the primary trap 101 with heater 116 and then backflushing the primary trap 110 while continuing to heat it with heater 116, the remaining sample in the primary trap 101 is transferred to the cold secondary trap 120, thereby delivering the remaining sample to the cold secondary trap 120. The secondary trap 120 then contains all the target compounds, where CO2 is effectively removed. Multiple valves 140 configure the primary trap 110 and the secondary trap 120 and facilitate flow from the primary trap 110 to the secondary trap 120 during step 207, as... Figure 3D As shown. During step 207, heater 116 heats primary trap 110 to a temperature in the range of 100°C to 200°C.

[0037] In step 208, the secondary trap 120 is preheated under no-flow conditions to achieve a faster release rate once flow toward GC 160 is generated. During step 208, valves 140 isolate the primary trap 110 and the secondary trap 120 from the rest of the system 100, such as... Figure 3C As shown and as referenced above in steps 203 and Figure 3CAs described. Even when using a detector unaffected by large amounts of CO2, any CO2 not removed from the sample may cause sample defocusing during preheating by causing the compounds to expand in both directions of the secondary trap 120 as the CO2 becomes volatile. Therefore, the sample cannot be injected rapidly because the volume can actually be too large and may far exceed the previously explained maximum total volume of 0.1 cc. Furthermore, since peak widths during gas chromatography are related to the diffusion rate of the target compound relative to the carrier gas, large amounts of CO2 co-eluted with some target compounds may actually require these compounds to be subject to a CO2 carrier gas composition with a diffusion rate much lower than typical GC carrier gases (helium and hydrogen), resulting in very large peak widths and poor separation between them. Therefore, CO2 removal not only prevents signal attenuation at the detector (mass spectrometer, etc.) but also avoids other adverse effects on the analysis.

[0038] In step 209, the secondary trap 120 is connected in series with the carrier gas flow leading to GC 160 to rapidly transfer the sample to the GC column. An optional focusing trap 130 can be used to focus the sample at near-liquid nitrogen temperatures to achieve even faster GC injection rates and even narrower on-column peaks. For example, process 200 includes step 210 of cooling the focusing trap and step 211 of focusing the sample using the focusing trap. Due to the narrower peaks, the time required to separate the compound of interest and the separation capability of the GC column are both lower. That is, if the GC peak width is only 3 seconds, baseline separation can be achieved by separating it from nearby peaks by only 3 seconds, while a peak with a width of 6 seconds requires a 6-second separation, thus requiring longer columns, thicker column films, and typically longer analysis times, thus impacting laboratory productivity. CF4 and other ultralight and / or highly volatile compounds may penetrate the focusing trap 130, but they have unique ions and will be well separated from those less volatile compounds retained by the focusing trap 130. Therefore, achieving the narrowest peak width and separation for other compounds is not important for these compounds. In step 211, the secondary trap 120 is heated to a temperature in the range of 150°C to 200°C using heater 136. After focusing, the focusing trap 130 is heated to 50°C to 100°C during step 209 to rapidly release all compounds of interest into the GCMS. Because there is no adsorbent inside the focusing trap 130 and only extremely low temperatures are used to retain the target compounds, lower desorption temperatures can be used compared to the primary trap 110 or the secondary trap 120.

[0039] Figure 3F The illustration shows an example of flow from secondary trap 120 to GC 160 facilitated by valves 140 in a system excluding the focusing trap 130. Figure 3FAs shown, (multiple) valves 140 facilitate flow from the secondary trap 120 in the opposite direction to the flow into the secondary trap 120 during steps 202 and 207; the compound exits the secondary trap 120 through an opening in step 209, and enters the secondary trap 120 through the opening in steps 202 and 207.

[0040] Figure 3G The illustration shows an example of flow from the secondary trap 120 through the focusing trap 130 to the GC 160, facilitated by temperature control of the valve(s) 140 and the focusing trap 130 in a system including a focusing trap 130. Figure 3G As shown, valves 140 facilitate flow from secondary trap 120 in the opposite direction to the flow into secondary trap 120 during steps 202 and 207; compounds exit secondary trap 120 through openings in step 211, and enter secondary trap 120 through the same openings in steps 202 and 207. Compounds enter GC 160 through focusing trap 130, entering from one end and exiting from the other. Alternatively, a PLOT column can be used for focusing to ensure that CF4 and other ultralight and / or highly volatile compounds are retained, but in any case, the focusing trap can be forward-purged (rather than backwashed) to GC 160.

[0041] When the target compound list includes compounds with higher and lower volatility than CO2, the techniques described herein analyze any gas containing trace amounts of volatile compounds via GCMS, which is related to their ability to be collected on an adsorbent trap at a specific trapping temperature. This requirement applies to greenhouse gases, as many are more volatile than CO2, while others are less volatile. In particular, the US EPA method OTM-50, used for analyzing PFAS / VFC compounds from C1 to C8 in flue gas, can benefit significantly from this new solution. Standard pre-concentration techniques (EPA methods TO-14A, TO-15, TO-15A) already used to analyze toxic chemicals in the air must employ two separate analyses. The first analysis measures CF4 in a small volume because CO2 cannot be removed; this volume is therefore limited to avoid excessive expansion of the focusing gas due to the need to inject CO2 into the GC. The second analysis purges CF4 and CO2, followed by analysis of C2 PFAS, C1 VFC, and all less volatile compounds. With this novel capture system that uniquely eliminates CO2 while quantitatively recovering all other compounds in the OTM-50 with a full volume of 200cc, the cost per sample analysis is reduced (one run instead of two), and the sensitivity to the lightest compound CF4 is also improved due to the ability to capture and inject a larger volume of sample gas.

[0042] Therefore, according to the foregoing, some embodiments of this disclosure relate to a method performed in a system including a primary trap, a secondary trap, a gas chromatograph (GC), and one or more valves. Additionally or alternatively, in some embodiments, the method includes: trapping a first compound more volatile than carbon dioxide (CO2), a second compound less volatile than CO2, and CO2 using the primary trap, including: using one or more valves to facilitate inflow into the primary trap through a first opening in a first direction. Additionally or alternatively, in some embodiments, the method includes: after trapping the first compound, the second compound, and CO2, eluting the first compound from the primary trap to the secondary trap using one or more valves, while retaining CO2 and the second compound using the primary trap, including: using one or more valves to facilitate outflow from the primary trap through a second opening in a first direction, different from the first opening of the primary trap. Additionally or alternatively, in some embodiments, the method includes: after eluting a first compound from a primary trap to a secondary trap, purging CO2 from the primary trap using one or more valves and an inert gas without transferring the CO2 to the secondary trap, while retaining a second compound using the primary trap. Additionally or alternatively, in some embodiments, the method includes: after purging CO2 from the primary trap, transferring the second compound from the primary trap to the secondary trap using one or more valves, including: backflushing the second compound in a flow manner from a first opening of the primary trap in a second direction opposite to the first direction. Additionally or alternatively, in some embodiments, after transferring the second compound from the primary trap to the secondary trap, injecting the first and second compounds into a GC using one or more valves for analysis by gas chromatography or gas chromatography-mass spectrometry without injecting CO2 into the GC. Additionally or alternatively, in some embodiments, the method includes: after eluting a first compound from a primary trap and while opening a first opening of the primary trap using one or more valves, isolating a secondary trap from the primary trap using one or more valves; and while isolating the secondary trap from the primary trap using one or more valves, raising the temperature of the primary trap to desorb CO2 from the primary trap; and retaining a second compound on the primary trap and retaining the first compound on the secondary trap. Additionally or alternatively, in some embodiments, the method includes: after eluting a first compound from the primary trap, while opening the first opening of the primary trap using one or more valves and while raising the temperature of the primary trap to desorb CO2 from the primary trap: coupling the primary trap to a vacuum reservoir using one or more valves; and measuring the amount of CO2 using a vacuum sensor to measure pressure changes in the system. Additionally or alternatively, in some embodiments, the pressure in the primary trap is higher than atmospheric pressure while purging CO2 from the primary trap.Additionally or alternatively, in some embodiments, the method includes: after eluting the first compound from the primary trap to the secondary trap, reducing the pressure in the primary trap before and / or simultaneously purging CO2 from the primary trap. Additionally or alternatively, in some embodiments, the method includes: after transferring the second compound to the secondary trap, cooling the focusing trap; and using one or more valves to transfer the first and second compounds from the secondary trap to the focusing trap to reduce the volume of the first and second compounds.

[0043] Some embodiments of this disclosure relate to a system including a primary trap comprising a first end and a second end opposite the first end, the primary trap being configured to trap a first compound more volatile than carbon dioxide (CO2), a second compound less volatile than CO2, and CO2. Additionally or alternatively, in some embodiments, the system includes a secondary trap. Additionally or alternatively, in some embodiments, the system includes a gas chromatograph (GC). Additionally or alternatively, in some embodiments, the system includes one or more valves. In some embodiments, the one or more valves are configured to: facilitate inflow into the primary trap in a first direction through a first opening of the primary trap while the primary trap traps the first compound, the second compound, and CO2. Additionally or alternatively, in some embodiments, one or more valves are configured to: after capturing the first compound, the second compound, and CO2, elute the first compound from the primary trap to the secondary trap, while retaining CO2 and the second compound using the primary trap, including: using one or more valves to facilitate outflow from the primary trap in a first direction through a second opening of the primary trap, different from the first opening of the primary trap. Additionally or alternatively, in some embodiments, one or more valves are configured to: after eluting the first compound from the primary trap to the secondary trap, purge CO2 from the primary trap using an inert gas without transferring CO2 to the secondary trap, while retaining the second compound using the primary trap. Additionally or alternatively, in some embodiments, one or more valves are configured to: after purging CO2 from the primary trap to the secondary trap, transfer the second compound from the primary trap to the secondary trap, including: backflushing the second compound in a second direction opposite to the first direction from the first opening of the primary trap in a flow pattern. Additionally or alternatively, in some embodiments, one or more valves are configured to inject the first and second compounds into the GC for analysis by gas chromatography or gas chromatography-mass spectrometry after transferring the second compound from the primary trap to the secondary trap, without injecting CO2 into the GC. Additionally or alternatively, in some embodiments, one or more valves are also configured to open a first opening of the primary trap and isolate the secondary trap from the primary trap after eluting the first compound from the primary trap; the system further includes a heater configured to raise the temperature of the primary trap to desorb CO2 from the primary trap while isolating the secondary trap from the primary trap using one or more valves, wherein the primary trap is further configured to retain the second compound while the one or more valves open the first opening of the primary trap and isolate the secondary trap from the primary trap; and to retain the first compound on the secondary trap while the one or more valves open the first opening of the primary trap and isolate the secondary trap from the primary trap.Additionally or alternatively, in some embodiments, the system further includes a vacuum sensor configured to measure pressure changes in the system to measure the amount of CO2 after one or more valves have eluted a first compound from the primary trap, while one or more valves have opened a first end of the primary trap, and while the temperature of the primary trap has increased to desorb CO2 from the primary trap; and a vacuum reservoir, wherein one or more valves are further configured to couple the primary trap to the vacuum reservoir. Additionally or alternatively, in some embodiments, the pressure in the primary trap is higher than atmospheric pressure while CO2 is being purged from the primary trap. Additionally or alternatively, in some embodiments, the system further includes a vacuum pump configured to reduce the pressure in the primary trap after the first compound has been eluted from the primary trap to the secondary trap, and before and / or simultaneously with the purging of CO2 from the primary trap. Additionally or alternatively, in some embodiments, the system includes a focusing trap configured to be cooled after one or more valves have transferred the second compound to the secondary trap, wherein the one or more valves are also configured to transfer the first and second compounds from the secondary trap to the focusing trap to reduce the volume of the first and second compounds.

[0044] Although examples have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will be apparent to those skilled in the art. These changes and modifications should be understood to be included within the scope of the examples of this disclosure as defined by the appended claims.

Claims

1. A method comprising: In a system that includes a primary trap, a secondary trap, a gas chromatograph (GC), and one or more valves: The primary trap is used to trap a first compound that is more volatile than carbon dioxide (CO2), a second compound that is less volatile than CO2, and CO2, comprising: using the one or more valves to facilitate the flow of the primary trap through a first opening in the primary trap in a first direction; After capturing the first compound, the second compound, and the CO2, the first compound is eluted from the primary trap to the secondary trap using the one or more valves, while the CO2 and the second compound are retained using the primary trap, including: using the one or more valves to facilitate the outflow of the primary trap in the first direction through a second opening of the primary trap that is different from the first opening of the primary trap; After the first compound is eluted from the primary trap to the secondary trap, the CO2 is purged from the primary trap using the one or more valves and an inert gas without transferring the CO2 to the secondary trap, while the second compound is retained using the primary trap. After purging the CO2 from the primary trap, transferring the second compound from the primary trap to the secondary trap using one or more valves includes: backflushing the second compound in a flow form from the first opening of the primary trap in a second direction opposite to the first direction; and After the second compound is transferred from the primary trap to the secondary trap, the first compound and the second compound are injected into the GC using one or more valves for analysis by gas chromatography or gas chromatography-mass spectrometry without injecting CO2 into the GC.

2. The method according to claim 1, further comprising: After the first compound is eluted from the primary trap and while the first opening of the primary trap is opened using the one or more valves: The secondary trap is isolated from the primary trap using one or more of the valves; and While using one or more valves to isolate the secondary trap from the primary trap: Increase the temperature of the primary trap to desorb the CO2 from the primary trap; as well as The second compound is retained on the primary trap and the first compound is retained on the secondary trap.

3. The method according to claim 2, further comprising: After the first compound is eluted from the primary trap, while simultaneously opening the first opening of the primary trap using one or more valves and raising the temperature of the primary trap to desorb CO2 from the primary trap: The primary trap is coupled to the vacuum reservoir using one or more of the valves; and The amount of CO2 is measured by measuring the pressure change of the system using a vacuum sensor.

4. The method of claim 1, wherein the pressure in the primary trap is higher than atmospheric pressure while the CO2 is being purged from the primary trap.

5. The method according to claim 1, further comprising: After eluting the first compound from the primary trap to the secondary trap, the pressure in the primary trap is reduced before and / or simultaneously before purging the CO2 from the primary trap.

6. The method according to claim 1, further comprising: After the second compound is transferred to the secondary trap: Cooling the focusing trap; as well as The first compound and the second compound are transferred from the secondary trap to the focusing trap using one or more valves to reduce the volume of the first compound and the second compound.

7. A system comprising: A primary trap includes a first end and a second end opposite to the first end, the primary trap being configured to trap a first compound that is more volatile than carbon dioxide (CO2), a second compound that is less volatile than CO2, and CO2. Secondary trap; Gas chromatograph (GC); and One or more valves are configured to: While the primary trap captures the first compound, the second compound, and the CO2, it promotes the flow of the primary trap into the primary trap through the first opening in a first direction; After capturing the first compound, the second compound, and the CO2, eluting the first compound from the primary trap to the secondary trap while retaining the CO2 and the second compound using the primary trap includes: using the one or more valves to facilitate outflow of the primary trap in the first direction through a second opening of the primary trap that is different from the first opening of the primary trap; After the first compound is eluted from the primary trap to the secondary trap, the CO2 is purged from the primary trap with an inert gas without transferring the CO2 to the secondary trap, while the second compound is retained using the primary trap. After purging the CO2 from the primary trap, transferring the second compound from the primary trap to the secondary trap includes: backflushing the second compound in a flow form from the first opening of the primary trap in a second direction opposite to the first direction; and After the second compound is transferred from the primary trap to the secondary trap, the first and second compounds are injected into the GC for analysis by gas chromatography or gas chromatography-mass spectrometry without injecting CO2 into the GC.

8. The system according to claim 7, wherein: The one or more valves are further configured to: after eluting the first compound from the primary trap, open the first opening of the primary trap and isolate the secondary trap from the primary trap; the system further includes: The heater is configured to: while isolating the secondary trap from the primary trap using one or more valves, raise the temperature of the primary trap to desorb the CO2 from the primary trap, wherein: The primary trap is further configured to retain the second compound while one or more valves open the first opening of the primary trap and isolate the secondary trap from the primary trap; and While one or more valves open the first opening of the primary trap and isolate the secondary trap from the primary trap, the first compound is retained on the secondary trap.

9. The system according to claim 8, further comprising: A vacuum sensor is configured to measure pressure changes in the system to measure the amount of CO2 after one or more valves have eluted the first compound from the primary trap, while one or more valves have opened the first end of the primary trap, and while the temperature of the primary trap has been increased to desorb CO2 from the primary trap; and A vacuum reservoir, wherein one or more valves are further configured to couple the primary trap to the vacuum reservoir.

10. The system of claim 7, wherein the pressure in the primary trap is higher than atmospheric pressure while the CO2 is being purged from the primary trap.

11. The system of claim 7, further comprising a vacuum pump configured to: reduce the pressure in the primary trap after the first compound is eluted from the primary trap to the secondary trap, and before and / or simultaneously with the purging of CO2 from the primary trap.

12. The system according to claim 7, further comprising: A focusing trap is configured to be cooled after the one or more valves transfer the second compound to the secondary trap, wherein the one or more valves are also configured to transfer the first compound and the second compound from the secondary trap to the focusing trap to reduce the volume of the first compound and the second compound.

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