Systems and methods for matrix accelerated vacuum assisted sorbent extraction for improved sample preparation prior to GCMS analysis

Abstract

The technology disclosed herein can improve the extraction of chemicals prior to analysis by GC or GCMS. A liquid or solid sample can be placed in a sample container of a closed system under vacuum, which further includes a sample extraction device. The assembly can be placed in a three-zone heater that can control the temperature of the bottom of the sample container, the top of the sample container, and the sample extraction device, respectively. The flux of vapor from the bottom of the sample container into the headspace of the sample container can deliver compounds of interest to the sample extraction device, while matrix compounds can recondense in the headspace of the sample container to avoid delivery to the sample extraction device. The extraction can continue until a substantial amount of the compounds of interest are transferred to the adsorbent, and subsequently the extract is thermally desorbed into a GCMS for analysis.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 064,334, filed August 11, 2020, the entire disclosure of which is incorporated herein by reference for all purposes. Technical Field

[0003] This disclosure relates to sample preparation, and more specifically to systems and methods for preparing samples via diffusion vacuum extraction. Background Technology

[0004] Gas chromatography / mass spectrometry (GCMS) has become a widely used technique for measuring chemicals with boiling points ranging from -253°C (e.g., hydrogen) to over 600°C (e.g., 6-8 ring PAHs). For compounds to be GCMS-compatible, they must have reasonably high vapor pressures (typically -50°C to 400°C) within the operating limits of the technique, while being sufficiently thermally stable to reach the detector, for example, through the GC column in the gas phase. Before GCMS injection, the sample can be cleaned so that only GC-compatible compounds are introduced into the GC. In some cases, non-GC-compatible compounds can deposit at the GC column inlet or on the column itself, leading to the adsorption or reaction (reduction in abundance) of many compounds, thus affecting the accuracy of the measurement. Some compounds can thermally decompose into all new compounds, creating so-called artificial traces, which can lead analysts to believe that these artificial traces are actually contained within the sample when they are not.

[0005] Furthermore, GCMS systems can be sensitive to excessive water injection, as too much water can damage the GC column, interact with the co-injected target compound, and cause signal suppression in the mass spectrometer. Even small amounts of water (e.g., 0.1-0.2 μL) can alter the vacuum within the mass spectrometer, leading to reduced ionization efficiency or increased gas-phase collisions, which decreases ion transfer efficiency to the electron multiplier or other ion detectors.

[0006] Several techniques can extract GCMS-compatible compounds from a variety of matrices (water, beverages, blood, urine, food, consumer products, etc.), but these techniques may have limitations that prevent them from achieving the ultimate goals of recovering GC-compatible compounds, excluding non-GC-compatible compounds, and reducing or minimizing the incorporation of volatile sample matrices (e.g., water, alcohols) into the extract. Some extraction techniques use a headspace above the liquid or solid sample for the extraction process, as the headspace contains only volatile or at least semi-volatile compounds, thus eliminating non-volatile components of the sample from the extract. Other techniques requiring contact with the sample may be less effective in removing non-volatile compounds from the extract and will not be discussed further. Those direct contact techniques include solvent extraction (liquid / liquid extraction, Soxhlet extraction, etc.), total immersion SPME, stirred bar adsorption extraction (SBSE), Hi-Sorb, solid-phase extraction, etc.

[0007] The objectives of sample extraction techniques may include:

[0008] Increase sensitivity

[0009] Increase accuracy

[0010] Reduce interference

[0011] Reduce artificial traces

[0012] Reduce analysis time

[0013] Increase the boiling point range of the compounds (to include at least a complete list of targets).

[0014] Improve the recovery of polar and nonpolar GC-compatible compounds

[0015] Improve the recovery of thermally unstable compounds

[0016] The ability to process liquid and solid samples or mixtures thereof

[0017] Provide multi-sample automation

[0018] Reduce legacy

[0019] Maintain the cleanliness of the analyzer

[0020] Eliminate the use of hazardous solvents

[0021] The following are some of the static and dynamic headspace techniques that have been used or recommended for GCMS sample preparation, along with their main drawbacks associated with the list above:

[0022] Purge and trap (1976) - limited to volatile compounds boiling at 220°C. Suffering from contamination, residue, and matrix interference. Long passageway leading to the trap and analyzer.

[0023] Vacuum distillation (US EPA, 1990) requires liquid nitrogen (expensive and difficult to use), has poor water vapor removal, is limited to compounds that boil at 250°C, and is difficult to automate. No commercial system has yet been developed.

[0024] SPME (1990) - Limited phases on fibers cause matrix interference, resulting in high retention (1%-10%) in the next analysis, limited to compounds that boil at 300°C.

[0025] SPME ARROW (2015) – has 10 times more phases than SPME, but legacy issues remain, including poor recovery of heavier compounds and a poor boiling point range.

[0026] VASE (2016) – Vacuum-assisted adsorbent extraction. Poor moisture repellency leads to inconsistencies in analysis, long extraction times, and reduced vacuum as extraction temperature increases.

[0027] PECE (2018) - Moisture condensation on the adsorbent trap produces a "thermal flush," which causes many compounds to migrate from the adsorbent back into the original sample matrix.

[0028] FEVE (2019) - Total Evaporation Vacuum Extraction. It does not create a closed system, therefore many compounds that boil at 100°C are not retained. It is not suitable for samples containing non-dissolved solids. Summary of the Invention

[0029] This disclosure relates to sample preparation, and more specifically to systems and methods for preparing samples via diffusion vacuum extraction. The techniques disclosed herein can remove non-volatile compounds from a sample, efficiently recover the target compound of interest, and remove as much moisture as possible prior to GCMS injection, including additional removal of moisture from the sample extraction apparatus after extraction.

[0030] This document discloses a matrix-accelerated vacuum-assisted adsorbent extraction (MA-VASE) technique. In some embodiments, a sample vial containing (e.g., liquid and / or solid) a sample is coupled to a sample extraction device comprising one or more adsorbents via a vacuum sleeve. A vacuum can be applied to the system, and the temperature of three zones can be independently controlled—zone A at the bottom of the sample vial, zone B at the headspace of the sample vial, and zone C at the adsorbent in the adsorbent extraction device. For example, zone B can be the coldest, and zone A can be the hottest. In some embodiments, in this configuration, one or more volatile and / or semi-volatile compounds of the sample can be transferred to the adsorbent under vacuum during diffusion. In some embodiments, the liquid matrix of the sample does not come into contact with the adsorbent during the sampling process because the sample is not aspirated through the adsorbent but is diffusely collected as gaseous and vapor-phase compounds evaporate in zone A and reach the adsorbent.

[0031] The techniques disclosed herein improve extraction efficiency and matrix removal when preparing samples prior to GCMS analysis. Some embodiments of this disclosure use a volatile matrix to facilitate the transfer of chemicals of interest from the sample to the sample extraction device 110. Multiple temperature zones during extraction can be generated and then eliminated in a closed system, which can accelerate the transfer of chemicals to the sample collection device while leaving non-volatile compounds. Non-volatile chemicals can be eliminated more effectively compared to solvent extraction or when the enrichment device is directly exposed to the sample matrix. Efficient removal of non-volatile chemicals from the sample helps keep the GCMS analyzer clean, allowing for maximum sample analysis times before analyzer maintenance. For example, after extracting volatile and semi-volatile compounds onto an adsorbent included in the sample extraction device, the adsorbent can be solvent extracted for liquid injection into a GCMS or LCMS, or the adsorbent can be directly thermally desorbed into the GCMS analyzer to improve analytical sensitivity. This improved sample extraction technique can be automated to allow hundreds of samples to be analyzed unattended in the laboratory.

[0032] The MA-VASE described herein is superior to the aforementioned techniques, including for preparing samples containing compounds with boiling points ranging from -50°C to approximately 550°C. The US EPA VOC methods for drinking water and wastewater analysis typically cover a boiling point range of approximately -25°C to 220°C; therefore, MA-VASE represents an improvement over current non-solvent-based EPA methods, particularly for compounds with higher boiling points. Currently, there are over 600 compounds on the EPA's Emerging Pollutant List, and many researchers are working to develop analytical methods for compounds that are not suitable for extraction methods found in current EPA methods. Compared to any other technique, MA-VASE has the potential to provide superior sample preparation solutions for a wider range of compounds. Attached Figure Description

[0033] Figures 1A to 1B An exemplary sample extraction system according to some embodiments is shown.

[0034] Figure 2 Exemplary methods for preparing samples according to some embodiments of the present disclosure are shown. Detailed Implementation

[0035] In the following description, reference is made to the accompanying drawings, which form part of the description, and specific examples that can be practiced are shown by way of illustration. It should be understood that other examples and structural changes may be used without departing from the scope of the examples in this disclosure.

[0036] This disclosure relates to sample preparation, and more specifically to systems and methods for preparing samples via diffusion vacuum extraction. The techniques disclosed herein can remove non-volatile compounds from a sample, efficiently recover the target compound of interest, and remove as much moisture as possible prior to GCMS injection, including additional removal of moisture from the sample extraction apparatus after extraction.

[0037] This document discloses a matrix-accelerated vacuum-assisted adsorbent extraction (MA-VASE) technique. In some embodiments, a sample vial containing (e.g., liquid and / or solid) a sample is coupled to a sample extraction device comprising one or more adsorbents via a vacuum sleeve. A vacuum can be applied to the system, and the temperature of three zones can be independently controlled—zone A at the bottom of the sample vial, zone B at the headspace of the sample vial, and zone C at the adsorbent in the adsorbent extraction device. For example, zone B can be the coldest, and zone A can be the hottest. In some embodiments, in this configuration, one or more volatile and / or semi-volatile compounds of the sample can be transferred to the adsorbent under vacuum during diffusion. In some embodiments, the liquid matrix of the sample does not come into contact with the adsorbent during the sampling process because the sample is not aspirated through the adsorbent but is diffusely collected as gaseous and vapor-phase compounds evaporate in zone A and reach the adsorbent.

[0038] The techniques disclosed herein improve extraction efficiency and matrix removal when preparing samples prior to GCMS analysis. Some embodiments of this disclosure use a volatile matrix to facilitate the transfer of chemicals of interest from the sample to the sample extraction device 110. Multiple temperature zones during extraction can be generated and then eliminated in a closed system, which can accelerate the transfer of chemicals to the sample collection device while leaving non-volatile compounds. Non-volatile chemicals can be eliminated more effectively compared to solvent extraction or when the enrichment device is directly exposed to the sample matrix. Efficient removal of non-volatile chemicals from the sample helps keep the GCMS analyzer clean, allowing for maximum sample analysis times before analyzer maintenance. For example, after extracting volatile and semi-volatile compounds onto an adsorbent included in the sample extraction device, the adsorbent can be solvent extracted for liquid injection into a GCMS or LCMS, or the adsorbent can be directly thermally desorbed into the GCMS analyzer to improve analytical sensitivity. This improved sample extraction technique can be automated to allow hundreds of samples to be analyzed unattended in the laboratory.

[0039] The MA-VASE described herein is superior to the aforementioned techniques, including for preparing samples containing compounds with boiling points ranging from -50°C to approximately 550°C. The US EPA VOC methods for drinking water and wastewater analysis typically cover a boiling point range of approximately -25°C to 220°C; therefore, MA-VASE represents an improvement over current non-solvent-based EPA methods, particularly for compounds with higher boiling points. Currently, there are over 600 compounds on the EPA's Emerging Pollutant List, and many researchers are working to develop analytical methods for compounds that are not suitable for extraction methods found in current EPA methods. Compared to any other technique, MA-VASE has the potential to provide superior sample preparation solutions for a wider range of compounds.

[0040] Figures 1A to 1B Exemplary sample extraction systems 100 and 130 according to some embodiments are shown. In some embodiments, sample extraction systems 100 and 130 may include one or more sample vials 104 containing (e.g., liquid or solid) a sample 102, one or more sample extraction devices 110, and a vacuum sleeve 106. In some embodiments, sample extraction device 110 may include one or more adsorbents 112a and 112b, a plurality of external seals 114a-114c, a port 115, and a valve 116.

[0041] In some implementation schemes, Figure 1A The system 100 shown may include ten sample extraction devices 110, each coupled to a sample vial 104. For example, Figure 1A The view shown is one of five rows of two pairs of sample extraction devices 110-sample vials 104. In some embodiments, extraction of ten samples can be performed simultaneously (e.g., manually, fully automated, or partially automated).

[0042] In some embodiments, system 130 can be used to extract one sample at a time. In some embodiments, system 130 can be used to repeatedly use multiple (e.g., two) sample extraction devices 110 in an alternating manner to continuously perform sample extraction and analysis. For example, sample extraction can be performed for the same duration as sample analysis, so that one sample can be extracted into a first sample extraction device 110 while another sample can be desorbed and analyzed from a second sample extraction device 110. Then, in this example, the sample extracted by the first sample extraction device 110 can be analyzed while the second sample extraction device 110 is reused to extract another sample. In some embodiments, the process can be repeated hundreds or thousands or more times with the same sample extraction device 110. If desired, the process can be fully or partially automated (e.g., with an automated sampler or other robot). In addition to the same components as system 100, system 130 may also include a vacuum port 132, a vacuum seal 134, and a sliding cover 136 for exchanging sample extraction devices 110.

[0043] In some embodiments, the sample extraction device 110 includes a single adsorbent. In some embodiments, the sample extraction device 110 includes two or more adsorbents 112a and 112b, which are arranged together with an adsorbent having the weakest affinity for one or more compounds of the sample, closest to the opening of the sample extraction device 110 through which one or more compounds of the sample enter the sample extraction device 110, and which are arranged away from the opening of the sample extraction device 110 along with an adsorbent having a stronger chemical affinity. For example, adsorbent 112a has a lower chemical affinity for one or more compounds of the sample compared to adsorbent 112b. In this way, heavier compounds may be retained by the weaker adsorbent (e.g., an adsorbent with a reduced chemical affinity for one or more sample compounds) closer to the opening of the sample extraction device 110, and a higher surface area or a stronger adsorbent may be required so that lighter compounds adsorbed may pass through the weaker adsorbent for collection by the stronger adsorbent. This method reduces the temperature required to release all compounds during thermal desorption, which reduces the reaction of thermally unstable compounds and increases the lifespan of the adsorbent sampling device.

[0044] In some embodiments, the sample extraction device 110 may be coupled to the sample container 104 such that the outer surface of the sample extraction device 106 may be (e.g., substantially) kept outside the headspace of the sample container 104. In this way, for example, the outer surface of the sample extraction device 110 may remain uncontaminated by one or more compounds of the sample.

[0045] In some embodiments, the sample 102 to be extracted can be placed in a sample container 104 (e.g., a sample vial), and the sample extraction device 110 can be positioned on top of the sample container 104. For example, assembling the system 100 or 130 in this manner can create a vacuum seal between the sample container 104, the vacuum sleeve 106, and the sample extraction device 110. A vacuum can then be applied to the system via valve 116, port 115 of the sample extraction device 110, or other means (e.g., using a vacuum source). In some embodiments, the vacuum source is a vacuum pump or other system for removing gas from the closed system. In some embodiments, the vacuum is not used to “pull” the liquid or solid matrix through the adsorbents 112a-112b, but rather to expel gas from the headspace of the sample container 104 to accelerate the diffusion rate of the headspace compound, while also allowing for a “matrix-to-headspace” vapor transport mechanism, as described in more detail below. This vacuum level can be quite high, and can be limited, for example, to the vapor pressure of the volatile fraction of the matrix at the coldest part of the extraction system (for water, approximately 1 / 30 of atmospheric pressure at 25°C). th In some embodiments, the temperature of region B is ultimately controlled by a system vacuum. In some embodiments, sealing the sample extraction device 110 and sample container 104 (e.g., with a vacuum sleeve 106) can create a closed system in sample extraction system 100 or 130, wherein once the initial headspace compounds (e.g., air, nitrogen, other stationary gases) have been purged, substances cannot enter or leave the system.

[0046] In some implementations, three temperature zones are maintained during the extraction process. For example, these are... Figures 1A to 1B The zones are designated as Zone A, Zone B, and Zone C. In some embodiments, the system may include thermal insulation elements 122a and 122b between the temperature zones to prevent or reduce the direct temperature influence of each heater on adjacent zones to any extent. Heaters 124a-124c allow the temperature of each zone to be maintained, and some cooling controls (e.g., radiator 126, fan, or electronic cooling system) may be used to remove heat from Zone B, such as heat generated by matrix condensation, as will be described. In some embodiments, heat may be transferred from Zone A to Zone B, such as heat generated due to the condensation of water vapor in Zone B. Therefore, in some embodiments, effective cooling of Zone B may be critical for controlling the temperature difference between Zone A and Zone B, which in turn may increase or maximize the vapor flux of the sample and increase or maximize the extraction rate of the sample.

[0047] In some embodiments, creating temperature regions with different temperatures from each other can lead to rapid vapor and condensate formation. In some embodiments, for example, vapor and condensate can form much faster under a vacuum in system 100 or 130 than at atmospheric pressure, due to the higher mobility of gaseous molecules under vacuum. For example, an initial vacuum drawn into system 100 or 130 can allow for the generation of positive vapor flux at relatively low temperatures, as will be described in detail below.

[0048] In some embodiments, region A may contain the sample to be extracted (e.g., liquid and / or solid), although a portion of the sample may extend into region B, and as the extraction process proceeds, one or more compounds of the sample (e.g., volatile, semi-volatile) are transferred to adsorbents 112a-112b in region C. Heating the liquid sample in A causes it to expand (become less dense) and rise, thereby creating a mixing process, for example (e.g., without the use of mechanical, magnetic, or other stirring devices or agitators). As the temperature of the liquid (e.g., or solid) sample increases, the temperature may become closer to the boiling point of the liquid sample (e.g., the boiling point of the liquid contents within the solid sample, or the boiling point of the solid itself), and in general, the vapor pressure above (e.g., liquid or solid) sample 102, such as, for example, the vapor pressure in sample vial 104, may increase. As used herein, the term “boiling point” should be understood as the temperature at which the vapor pressure of the volatile liquid fraction of the sample is equal to the vapor pressure of the headspace of the sample container, and as previously stated, this temperature may be much lower than the standard boiling point temperature of the volatile matrix at atmospheric pressure. For example, water can boil at 25°C at a headspace pressure of 18 Torr, compared to boiling at 100°C at a headspace pressure of 760 Torr (standard atmosphere).

[0049] When heat in region A causes liquid (e.g., partially) to evaporate, chemicals within the sample can be similarly transported into the gas phase, even at temperature / pressure combinations well below the boiling point of the compound at atmospheric pressure. Because system 100 or 130 is a closed system, if the entire system 100 or 130 is brought to a single temperature, the pressure within system 100 or 130 can be increased until equilibrium is reached at that particular temperature, after which no further net transfer, such as from liquid to gas phase, will occur. In this example, the resulting conditions would likely cause the matrix to condense throughout system 100 or 130. However, this is not the case, for example, when system 100 or 130 has three temperature zones. In some embodiments, the three temperature zones of system 100 or 130 can cause continuous evaporation and condensation of the compound in sample 104, thereby creating a mixing effect of sample 104 within the system. Heating region A from below can increase the temperature of the volatile matrix, which can thereby reduce its density and cause it to rise within the sample matrix to achieve the mixing process, thus ensuring that the compound of interest is continuously presented to the surface for, for example, gas phase transport.

[0050] In some embodiments, region B may be isolated from region A (e.g., by insulation 122a) and may be at a lower temperature than region A. Therefore, once the vapor expands into region B, energy can be drawn from the vapor molecules through collisions in the cooler region (which occur more quickly due to the higher diffusion rate under vacuum), and the compound can coalesce back into a liquid, for example as an aerosol or droplet on the surface of sample container 104 in region B. This gas-to-liquid conversion can reduce the net flow rate to (e.g., substantially) zero because the system is closed during the extraction process, which allows the aerosol to “precipitate” in regions A and B, rather than continuing to move, for example, towards region C.

[0051] In some embodiments, chemicals less soluble in the matrix than the main matrix compound itself (e.g., water) may remain in the gas phase once released, contrary to condensation into aerosols and droplets. This tendency, for example, allows them to continue diffusing, enabling them to find one or more of adsorbents 112a and 112b in region C, where the adsorbents will be (e.g., diffusely) collected. In some embodiments, region C may be maintained at a temperature slightly higher than that of region B, which prevents or reduces the aggregation of undesirable volatile matrix compounds (e.g., water, alcohols, etc.) in region C. Thus, in some embodiments, the liquid matrix does not aggregate on adsorbents 112a-112b during the sample extraction process. For example, in the case of an aqueous matrix, the higher temperature of region C may result in a relative humidity of less than 100%. Furthermore, in some embodiments, one or more adsorbents 112a-112b may be selected to not absorb or adsorb the main matrix compound (e.g., typically and primarily aqueous or water / alcohol mixtures). Even if aerosols generated by the recondensation of the matrix in region B accidentally enter region C, the temperature of region C can allow the aerosols to "evaporate" from region C and redistribute to region B, because, for example, since the temperature of region C is higher than that of region B, the energy levels of the molecules in region C can be higher than the energy levels of the compounds in region B.

[0052] During matrix condensation in zone B, heat can be released with the condensation of vapor (e.g., heat from evaporation), and this heat must be removed from zone B to maintain a temperature lower than that of zones A and C, and, for example, as close as possible to the setpoint temperature. In some embodiments, the temperature in zone B can be maintained by: reducing the temperature of zone A (e.g., thus reducing the required condensation and heat transfer rate in zone B), causing zone B to passively release sufficient heat, or by providing heat transfer and / or heat removal mechanisms such as a radiator 126 with heat transfer fins, by using a fan, or by using a circulating coolant around zone B. Generally, the faster the reflux process (e.g., the higher the temperature of zone A relative to the temperature of zone B), the greater the heat that needs to be removed from zone B, but faster reflux can also increase vapor flux and reduce the extraction time required to essentially recover all compounds of interest.

[0053] When the liquid evaporates, a transition layer exists at the liquid / vapor boundary, where the composition changes from 100% liquid to 100% gaseous phase over, for example, a non-zero distance. Thus, at some point in the transition zone, the matrix is ​​90% liquid and 10% gas, then 80% liquid and 20% gas, and so on, until, for example, a point is reached where 100% gaseous phase is achieved. While this distance may be relatively small on a macroscopic scale, it may not be small on a molecular scale. In the MA-VASE process disclosed herein, a positive airflow toward the headspace of sample container 104 may exist, so that heavier compounds that might resist entering the headspace when using standard mechanical mixing can be “pushed” into the headspace due to being trapped during the phase transition and due to the forced flow of the matrix. When the vapor recondenses in the cooler region B, similar molecules may preferentially condense against each other, and the target compounds are more likely to remain in the gaseous phase, where they can continue to reach adsorbents 112a-112b. The aerosol can either precipitate directly back into the sample matrix (e.g., in region A) or condense under gravity and "discharge" downwards back into sample 102 at the bottom of sample container 104. Once back in region A, the evaporation and condensation of the compound can be repeated continuously to complete the extraction process. This evaporation / atomization method can increase the surface area of ​​the sample (e.g., without the use of physical stirring or agitation devices). Other systems / techniques that mix the sample at isothermal temperatures do not utilize the vapor flux in the direction of the sample extraction apparatus 110, and therefore can achieve slower extraction rates due to the lack of vapor flux. Furthermore, techniques performed at atmospheric pressure instead of under vacuum can also result in slower extraction rates.

[0054] The MA-VASE technique presented in this paper addresses several issues inherent in other extraction techniques. For example, adsorbents 112a-112b can be placed close enough to sample 102 to eliminate the need for a delivery line, yet far enough away to avoid contact with the condensate matrix. In techniques that purge samples via a delivery line, the use of the line can cause compounds to react on the inner surface of the line, resulting in the permanent adhesion of very heavy (but partially volatile) compounds to those surfaces. This can create a film that retains the target compound in future extraction events, leading to inconsistent compound recovery across runs. Method consistency is critical between runs and over longer periods (hundreds of samples), but is unattainable in most extraction techniques, particularly those that use a delivery line between the sample and the extraction apparatus. For instance, MA-VASE eliminates the need for a delivery line by placing adsorbents 112a-112b on top of sample container 104. The sample container is used only once and then discarded, eliminating the possibility of residue (contamination) from runs with higher concentrations of sample, as seen in other extraction systems where portions of the extraction system are used multiple times.

[0055] In some implementations, the generation of a dynamic flow exiting region A and a static diffusion flow in region B (because most of the vapor is recondensed to eliminate the vapor flow) allows the target compound to accumulate on adsorbents 112a-112b in region C during diffusion with minimal channeling into the adsorbent, since the net flow in region C is zero at least relative to >99% of the sample (or 99.99+% of the sample for trace element analysis). Channeling, i.e., one or more compounds being pushed deeper into the adsorbent than using diffusion transfer techniques, can be a challenge for dynamic headspace systems (e.g., purge and trap). Reduction of channeling improves recovery during thermal desorption of the sample extraction device 110, reduces the baking time required to clean the adsorbents 112a-112b (and thus reduces the amount of thermal stress on the adsorbent itself), and reduces the retention of one or more compounds between runs. Dynamic headspace techniques can have a residue (compound-dependent) typically in the range of 0.1%–1%, while static diffusion sampling techniques such as MA-VASE can show a residue level well below 0.01% (e.g., due to reduced channeling).

[0056] MA-VASE can also eliminate the need for mechanical mixing. For example, many SPME systems use high-speed stirrers to improve the recovery of heavier target compounds. Mechanical mixing continuously refreshes the boundary layer to increase the rate of transport to the headspace. Relatively slow stirring rates refresh the upper surface of the sample, and most SPME methods using mechanical mixing show improved recovery at high mixing rates, e.g., the higher the better. When mixing at high speeds rather than low speeds, the increase in recovery outweighs the effect of increasing the meniscus size. In fact, high-speed mixing can cause the liquid matrix to “splash” or “throw” into the headspace, which can deliver all droplets of the sample matrix itself to the SPME fiber, unlike the desired “clean” headspace methods that only allow gas phase molecules to reach the fiber. This aerosol transfer can increase the recovery of low vapor pressure target compounds, but at the cost of transferring non-volatile compounds, including salts, proteins, carbohydrates, etc., to the fiber, which can reduce fiber lifetime and lead to artificial traces during analysis. For example, MA-VASE evaporation of liquid (e.g., or solid) sample 102 at a temperature below its boiling point can produce little or no aerosol directly from sample 102. In some embodiments, the only aerosols produced in the MA-VASE method are those formed in condensation zone B. For example, these condensed aerosols may consist only of volatile and semi-volatile compounds, since non-volatile compounds do not evaporate. Matrix acceleration (vapor flux) can be tuned by varying the temperatures of zones A and B, which can allow for increased or maximized recovery of compounds of interest while excluding heavier, non-GC-compatible compounds that may not enter the gas phase. Thus, MA-VASE can be an excellent way to transfer volatile and semi-volatile compounds from sample 102 to adsorbents 112a-112b by generating and then eliminating flux from the matrix itself to propel the target compound into the gas phase, rather than using mechanical stirring that may generate too much sample splashing within sample container 104.

[0057] During extraction, region A can be maintained at a constant temperature, typically higher than that of region B, or it can be gradually increased and decreased during cycling. In some embodiments, region A can be maintained at a higher temperature than region B even if the temperature in region A fluctuates periodically. In some embodiments, the temperature of region A can fluctuate periodically between temperatures higher and lower than those in region B. Periodically changing the temperature of region A can increase the vapor flux density compared to maintaining region A at a fixed temperature during extraction. The rate of temperature increase can be evaluated for different applications and sample types to determine the rate and amount of temperature change in region A that achieves the fastest extraction while providing the minimum amount of matrix transfer to sample extraction device 110. For example, a method can be developed to reduce or minimize the amount of water transferred to sample extraction device 110.

[0058] In some cases, during the extraction process, region A may be heated to a temperature lower than that of regions B or C once or multiple times, and region B may be heated to a temperature higher than that of regions A and C. Once region A is reheated, these temperatures can release any heavier compounds of interest adhering to the walls of sample container 104 in region B, allowing them to volatilize again and enter adsorbents 112a-112b. In some embodiments, the heavier compounds of interest may instead be partitioned into both regions A and C. In these cases, compounds transferred back to region A can be transferred to region C by reheating region A to the highest temperature of the three regions and bringing the temperature of region B back down to a temperature lower than that of regions A and C, allowing extraction from region A to region C to continue. In this way, for example, the recovery rate of heavy GC-compatible compounds can be increased or maximized.

[0059] In some cases, the temperature of region B can be temporarily (e.g., periodically) raised to the temperature of region A, while the temperature of region C is slightly higher than that of regions A and B, in order to release the heavier compounds collected in region B. This technique ensures that near-100% humidity conditions at the elevated temperature in region B can be used to help release the heaviest compounds from the inner walls of the sample container in region B, giving them another opportunity to diffuse into region C.

[0060] In some embodiments, when processing samples that may be thermally unstable, region B can be cooled to below room temperature so that region A can be maintained (e.g., substantially) room temperature (e.g., 25°C–40°C) during extraction. In some embodiments, when preparing samples of natural products, the temperature of region A can be 25°C–40°C, thereby avoiding temperatures above 40°C that could “cook” the natural products. With region A at temperatures within this range, for example, to achieve the desired throughput, region B can be at a temperature in the range of 0°C–10°C, and region C can be at 30°C or higher. For some samples, non-volatile fractions in the natural products can be “cooked” at temperatures as low as 40°C and produce artificial traces, but volatile fractions can be subjected to higher temperatures in region C without producing artificial traces. In some embodiments, the temperature of region C is lower than the temperature of region A. In some embodiments, the temperature of region C is higher than or equal to the temperature of region A.

[0061] In some embodiments, a volatile matrix (e.g., water and / or alcohol) may be added to the sample prior to the extraction of one or more volatile and / or semi-volatile compounds from the sample (e.g., solid). In some embodiments, this volatile matrix may facilitate the transfer of volatile and / or semi-volatile compounds from the sample (e.g., solid) to the gas phase. For example, when water and / or alcohol are added, followed by MA-VASE extraction, soil samples may be allowed to release their volatile and semi-volatile contents. In this case, the initial temperatures of zones A, B, and C may all be higher than the temperatures during the remainder of the extraction process to heat the solid sample in the liquid matrix sufficiently to achieve extraction of compounds of interest, for example, those otherwise locked within the solid sample matrix. In some embodiments, after a short extraction from solid to liquid, the temperatures of zones A, B, and C may be reduced to standard MA-VASE extraction temperatures, which ensures that the temperature of the adsorbents 112a-112b in zone C is sufficiently cold to achieve higher affinity for a potentially wide boiling point range of compounds of interest. For example, during pre-extraction, region B is at a lower temperature than regions A and C.

[0062] After the extraction period (5 minutes to 24 hours, depending on the matrix and compound to be measured, but typically 0.2 to 4 hours), all regions can be cooled while maintaining the temperature of region C slightly higher than that of regions A and B to prevent any condensation of the matrix in region C during cooling. During this period, in some embodiments, volatile matrix can be further removed from the sample extraction device 110 in region C because the system is still under vacuum, allowing any water or volatile matrix to quickly find its way to the cooler parts of the system (e.g., regions A and B), thereby achieving the ultimate goal of minimizing the amount of volatile matrix retained on or within the sample extraction device 110. When the extraction process is complete, the sample extraction device 110 can be removed from its components (e.g., sample container 104, vacuum sleeve 106) and can be thermally desorbed into the GCMS using one of many different thermal desorption systems.

[0063] Figure 2 An exemplary method 200 for preparing a sample according to some embodiments of the present disclosure is shown. In some embodiments, reference is made above. Figures 1A to 1B The described system 100 or 130 can be used to perform method 200. In some embodiments, one or more steps of method 200 can be automated by one or more processors storing instructions for performing the method (e.g., stored in a non-transitory computer-readable storage medium).

[0064] In some embodiments, the sample container 104, sample extraction device 110, and vacuum sleeve 106 may be connected together to form a closed system. When the sample container 104 is connected to the sample extraction device 110 and vacuum sleeve 106, the sample container 104 can contain (e.g., liquid or solid) a sample. In some embodiments, connecting the sample container 104, sample extraction device 110, and vacuum sleeve 106 can form a vacuum seal in system 100 or 130. In some embodiments, the sample container 104, sample extraction device 110, and vacuum sleeve 106 may be placed in a manner such as... Figures 1A to 1B In the three-zone heater shown, the temperatures of zone A, zone B, and zone C can be controlled (e.g., substantially) independently of each other.

[0065] In some embodiments, a vacuum 204 can be drawn onto system 100 or 130. In some embodiments, a vacuum source, such as a vacuum source configured to remove gas from a closed system, can be used to draw the vacuum. For example, a vacuum can be drawn through the top valve 116 or side port 115 of the sample extraction device 110. In some embodiments, the vacuum can be drawn in different ways. In some embodiments, a vacuum seal between the sample container 104, the sample extraction device 110, and the vacuum sleeve 106 can maintain a vacuum in the system during sample preparation.

[0066] In some embodiments, the temperatures of multiple zones of system 100 or 130 can be controlled independently of each other during process 200 using one or more heaters (e.g., heaters 124a-124c), radiators (e.g., radiator 126), and / or other heating and / or cooling systems. For example, zone B can be maintained at a lower temperature than zones A and C, and zone C can be at a lower temperature than zone A. In some embodiments, thermal insulation elements 122a and 122b and radiator 126 can help isolate the temperatures of zones A, B, and C from each other. In some embodiments, the temperature of zone A can be constant or can vary periodically during process 200.

[0067] In some embodiments, process 200 may collect one or more compounds of sample 208 in adsorbents 112a-112b. For example, one or more volatile or semi-volatile compounds of sample 102 (e.g., liquid, solid) may evaporate from region A to region B and, once in the gas phase, may be collected by adsorbents 112a-112b. In some embodiments, adsorbents 112a-112b may be selected to repel compounds of the matrix. For example, a hydrophobic adsorbent may be used to remove water from an aqueous sample. Furthermore, because the temperature of region B may be lower than that of region C, one or more compounds of the matrix reaching adsorbents 112a-112b may evaporate from adsorbents 112a-112b and transfer back to sample container 104.

[0068] In some embodiments, process 200 may include dehydrating sample collection device 106 (e.g., one or more adsorbents 112a-112b included therein) 210, such as by cooling regions A and B to a temperature (e.g., slightly lower) than the temperature in region C. Dehydrating sample collection device 106 in this way can remove matrix from adsorbents 112a-112b.

[0069] In some embodiments, method 200 may include 212 chemical analysis (e.g., by GC or GC-MS) of the compounds collected by adsorbents 112a-112b. In some embodiments, one or more compounds retained by adsorbents 112a-112b of sample extraction device 110 may be thermally desorbed from adsorbents 112a-112b or (e.g., extracted using a solvent) prior to analysis.

[0070] In some embodiments, one or more of the techniques disclosed herein may be (e.g., fully or partially) automated. For example, multiple sample containers 104, sample extraction devices 110, and vacuum sleeves 106 assemblies may be arranged in a sample tray, with heaters 124a, 124b, and 124c, a radiator 126, and insulation elements 122a and 122b integrated with the sample tray, thereby allowing the simultaneous preparation of multiple samples. In some embodiments, the automated sampler may operate a vacuum pump to evacuate all components, and the temperatures of regions A, B, and C may be computer-controlled to automate the preparation of multiple samples at once. In some embodiments, the automated sampler may then transfer sample extraction devices 110 (e.g., one after another) to the system for desorption or extraction and subsequent analysis of compounds retained by adsorbents 112a-112b. Thus, in some embodiments, the computer controlling the sample preparation process may include (e.g., via a non-transitory computer-readable medium) a memory storing instructions for performing one or more steps of one or more processes disclosed herein.

[0071] In some implementations, after the analysis of the sample is completed, the sample container 104, the vacuum sleeve 106, and the sample extraction device 110 can be baked or cleaned and reused according to one or more other methods.

[0072] The techniques disclosed in this paper can be used to improve the rate and quality of sample preparation prior to GCMS analysis. Almost every field using GCMS can benefit from these techniques, including:

[0073] Petrochemicals (plastics, synthetic materials)

[0074] Environment (drinking water, wastewater, soil, sludge)

[0075] Clinical (plasma, urine, respiratory condensate, lymph, tissue analysis, metabolomics)

[0076] Food and beverages (flavorings, odor compounds, contaminants, regulatory compounds)

[0077] Alcoholic beverages (beer, wine, spirits)

[0078] Consumer products (fragrances, odors, regulated pollutants)

[0079] Forensic medicine (drug abuse, accelerators)

[0080] Military (chemical warfare agents)

[0081] Some embodiments of this disclosure support manual or automated multi-sample analysis. As with other analytical methods, the recovered compound can be added to each sample prior to extraction to verify proper sample preparation.

[0082] Therefore, according to the foregoing, some embodiments of this disclosure relate to a closed system for preparing samples under vacuum, the system comprising: a sample container configured to hold a sample; an adsorbent; a first heater configured to apply a first temperature to a first portion of the sample container; a second heater configured to apply a second temperature, less than the first temperature, to a second portion of the sample container; and a third heater configured to apply a third temperature, greater than the second temperature, to the adsorbent. Alternatively, in some embodiments, the system further comprises a vacuum sleeve configured to form a vacuum seal between the sample container and a sample extraction device containing the adsorbent. Alternatively, in some embodiments, the sample extraction device includes a port or seal configured to be coupled to a vacuum source when the system is evacuated. Alternatively, in some embodiments, the adsorbent is disposed in the sample extraction device, which is configured to be removed from the system for analysis of one or more compounds in the sample. In addition to or alternatively, in some embodiments, the system further includes one or more radiators, fans, or cooling devices below room temperature configured to maintain the second temperature. In addition to or alternatively, in some embodiments, the first heater is further configured to periodically change the first temperature. In addition to or alternatively, in some embodiments, the system does not include a delivery line between the sample container and the adsorbent. In addition to or alternatively, in some embodiments, the system does not include a physical stirring device. In addition to or alternatively, in some embodiments, the adsorbent is configured to collect one or more compounds of the sample and repel the sample matrix.

[0083] Some embodiments relate to a method for preparing a sample in a closed system under vacuum, the method comprising: at a system including a sample container, an adsorbent, a first heater, a second heater, and a third heater, with a sample disposed in the sample container; applying a first temperature to a first portion of the sample container using the first heater; applying a second temperature, less than the first temperature, to a second portion of the sample container using the second heater; and applying a third temperature, greater than the second temperature, to the adsorbent using the third heater. Alternatively or additionally, in some embodiments, the method further comprises drawing a vacuum in the system via a vacuum pump; and maintaining the vacuum in the system after drawing the vacuum, wherein the first, second, and third temperatures are applied while maintaining the vacuum in the system. Alternatively or additionally, in some embodiments, the vacuum is drawn through a port or seal of a sample extraction device including the adsorbent. Alternatively or additionally, in some embodiments, the method further comprises maintaining the second temperature via one or more radiators, fans, or cooling devices below room temperature. Alternatively or additionally, in some embodiments, the method further comprises periodically changing the first temperature using the first heater. In addition or alternatively, in some embodiments, the method further includes collecting one or more compounds of the sample via the adsorbent; and repelling the matrix of the sample via the adsorbent. In addition or alternatively, in some embodiments, the method further includes, after collecting one or more compounds of the sample: removing the sample extraction device comprising the adsorbent from the system; and analyzing one or more compounds of the sample.

[0084] Although examples have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. Such 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 sealed system for preparing samples under vacuum, the system comprising: A sample container configured to hold the sample, wherein the bottom of the sample container is located within region A and the headspace of the sample container is located within region B. An adsorbent is located in region C, wherein region C is located in a region of the closed system that does not overlap with region A and / or region B, wherein the adsorbent is configured to extract one or more compounds from the sample; A first heater is disposed in the region A, and the first heater is configured to apply a first temperature to a first portion of the sample container; A second heater is disposed in the region B, and the second heater is configured to apply a second temperature, less than the first temperature, to a second portion of the sample container; One or more radiators, fans, or sub-room cooling devices are configured to maintain the second temperature in region B between region A and region C, region B including the second portion of the sample container; and A third heater is disposed in the region C, and the third heater is configured to apply a third temperature greater than the second temperature to the adsorbent to prevent condensation and retain the vapor of the sample matrix. A vacuum sleeve is configured to form a vacuum seal between the sample container and the sample extraction apparatus containing the adsorbent, creating a closed system in which substances cannot enter or leave the closed system once the initial headspace compound has been emptied.

2. The system of claim 1, wherein the sample extraction device includes a port or seal configured to be connected to a vacuum source when the system is evacuated.

3. The system of claim 1, wherein the adsorbent is disposed in a sample extraction device configured to be removed from the system for analysis of one or more compounds in the sample.

4. The system of claim 1, wherein the first heater is further configured to periodically change the first temperature.

5. The system of claim 1, wherein the system does not include a delivery line located between the sample container and the adsorbent.

6. The system according to claim 1, wherein the system does not include a physical stirring device.

7. The system of claim 1, wherein the adsorbent is configured to collect one or more compounds of the sample and repel the matrix of the sample.

8. A method for preparing a sample in a closed system under vacuum, the method comprising: At the closed system, the system includes a sample container, an adsorbent located in region C, a first heater located in region A, a second heater located in region B, and a third heater located in region C, wherein the adsorbent is configured to extract compounds from the sample, the sample is disposed in the sample container, and the bottom of the sample container is located in region A, and the headspace of the sample container is located in region B. The first temperature is applied to the first part of the sample container using the first heater; The second heater is used to apply a second temperature, lower than the first temperature, to the second part of the sample container; The second temperature within region B, which includes the second portion of the sample container, is maintained by one or more heat sinks, fans, or cooling devices below room temperature. The adsorbent is subjected to a third temperature greater than the second temperature using the third heater to prevent condensation and maintain the vapor of the sample matrix. Region C is above region A and region B and does not overlap with region A and / or region B. as well as A vacuum seal is formed between the sample container and the sample extraction device containing the adsorbent using a vacuum sleeve, creating the closed system in which substances cannot enter or leave the closed system once the initial headspace compound has been emptied.

9. The method according to claim 8, wherein the method further comprises: A vacuum is drawn into the system via a vacuum pump; as well as After evacuation, the vacuum in the system is maintained, wherein the first temperature, the second temperature, and the third temperature are applied while maintaining the vacuum in the system.

10. The method of claim 9, wherein a vacuum is drawn through a port or seal of the sample extraction device comprising the adsorbent.

11. The method according to claim 8, wherein the method further comprises: The first temperature is changed periodically using the first heater.

12. The method of claim 8, further comprising: One or more compounds from the sample are collected via the adsorbent; as well as The matrix of the sample is repelled by the adsorbent.

13. The method according to claim 12, wherein the method further comprises: After collecting the one or more compounds in the sample: Remove the sample extraction device containing the adsorbent from the system; as well as Analyze the sample for one or more compounds.

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