Columns with stationary phase thickness gradient

Abstract

A gas chromatography device for peak focusing of one or more target analytes is provided, the gas chromatography device comprising a chromatographic column having an inlet and an outlet. A stationary phase is deposited in the chromatographic column and has a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. The second thickness is at least about 10% greater than the first thickness. A method for peak focusing in a gas chromatography device, a method for verifying peak focusing in a gas chromatography device, and a gas chromatography device for manufacturing a chromatographic column with a positive thickness gradient are also provided.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 940,038, filed on November 25, 2019. The entire disclosure of the above provisional application is incorporated herein by reference.

[0003] Government support

[0004] This invention was made with government support under Grant OH011082 from the Centers for Disease Control and Grant FA8650-17-C-9106 from the U.S. Air Force, Air Force Materiel Board. The government has certain rights in this invention. Technical Field

[0005] The present disclosure relates to a gas chromatography apparatus including a chromatography column having a stationary phase with a positive thickness gradient to enhance peak focusing. Background Art

[0006] This section provides background information related to the present disclosure which is not necessarily prior art.

[0007] Gas chromatography (GC) is an analytical method for separating gas phase compounds via a separation column, which allows for the analysis and identification of compounds in a target sample. GC is widely used in many industries to separate and identify target analytes, such as volatile organic compounds or semi-volatile organic compounds. GC is particularly suitable for analyzing complex samples with multiple target analytes that need to be detected separately. GC works by observing the "peaks" of chemicals passing through a separation column. Therefore, samples with different chemicals or target analytes are introduced into the column via an injector. The column includes an internal material that is considered to be a stationary phase. Different parts of the sample pass through the column at different rates (due to the physical and chemical interactions of each chemical with the materials contained in the column). As the target analyte elutes and leaves the column, the detector can distinguish the material eluted over time based on the rate at which the analyte passes through the column. These analytes can be electronically identified and / or quantified during or after detection. It is desirable to improve the separation within the chromatographic column to improve performance and GC detection capabilities. Summary of the invention

[0008] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0009] In certain aspects, the present disclosure relates to a gas chromatography device for peak focusing of one or more target analytes. The chromatographic column has an inlet and an outlet, wherein the inlet receives a sample containing one or more target analytes that leave the column at the outlet. The stationary phase is deposited inside the chromatographic column and has a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. The second thickness is at least about 10% greater than the first thickness.

[0010] In one aspect, the first thickness is greater than or equal to about 10 nm to less than or equal to about 10 microns, and the second thickness is greater than or equal to about 30 nm to less than or equal to about 30 microns.

[0011] In one aspect, the second thickness is at least about 100% greater than or equal to the first thickness.

[0012] In one aspect, the second thickness is at least about 300% greater than or equal to the first thickness.

[0013] In one aspect, the chromatographic column is a microgas chromatographic column.

[0014] In one aspect, the stationary phase comprises a siloxane polymer.

[0015] In yet another aspect, the siloxane polymer includes at least one alkyl or aryl group comprising from 1 to 30 carbon atoms.

[0016] In one aspect, the cross-sectional shape of the chromatography column is selected from the group consisting of: circular, oval, rectangular and triangular.

[0017] The present disclosure also relates to a method for peak focusing in a gas chromatography device. The method includes introducing two or more target analytes into the inlet of a chromatographic column, and the chromatographic column includes a stationary phase deposited inside the chromatographic column and having a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. The second thickness is at least about 10% greater than the first thickness. The method also includes separating the two or more target analytes in the chromatographic column. The method also includes eluting the two or more target analytes from the outlet of the chromatographic column.

[0018] In one aspect, two or more target analytes are volatile organic compounds (VOCs).

[0019] In one aspect, at least one of the two or more target analytes comprises an aromatic compound, and the overall peak focusing rate for the aromatic compound is greater than or equal to about 25%.

[0020] In one aspect, at least one of the two or more target analytes comprises an alkane compound, and the total peak focusing rate for the alkane compound is greater than or equal to about 10%.

[0021] In one aspect, the first thickness is greater than or equal to about 10 nm to less than or equal to about 10 microns, and the second thickness is greater than or equal to about 30 nm to less than or equal to about 30 microns.

[0022] In one aspect, the second thickness is at least about 300% greater than or equal to the first thickness.

[0023] In one aspect, the chromatographic column is a micro gas chromatography column.

[0024] In yet another aspect, the stationary phase comprises a siloxane polymer comprising at least one alkyl or aryl group comprising from 1 to 30 carbon atoms.

[0025] In one aspect, the cross-sectional shape of the chromatography column is selected from the group consisting of: circular, oval, rectangular and triangular.

[0026] The present disclosure also relates to a method for verifying peak focusing in a gas chromatography device. The method includes performing a forward operation (forward operation) by introducing two or more target analytes into the inlet of a chromatographic column, and the chromatographic column includes a stationary phase deposited inside the chromatographic column and having a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. The second thickness is at least about 10% greater than the first thickness. The forward operation includes separating two or more target analytes in the chromatographic column and eluting two or more target analytes from the outlet of the chromatographic column. The method also includes performing a reverse operation (reverse operation) by introducing two or more target analytes into the outlet of the chromatographic column, and the chromatographic column includes a stationary phase. The reverse operation includes separating two or more target analytes in the chromatographic column and eluting two or more target analytes from the inlet of the chromatographic column. The method also includes comparing the chromatographic resolution (chromatographicresolution) from the forward operation and the reverse operation, wherein the peak focusing rate of two peaks corresponding to at least one pair of two target analytes is greater than 5%.

[0027] The present disclosure further relates to a method for manufacturing a gas chromatography device having a chromatographic column with a positive thickness gradient. The method includes adding a precursor liquid to the chromatographic column. The precursor liquid includes a stationary phase precursor and a low boiling point solvent, which volatilizes along the length of the chromatographic column to increase the concentration of the stationary phase precursor when the stationary phase precursor moves along the chromatographic column, thereby generating a stationary phase thickness gradient. The method also includes reacting or cross-linking the stationary phase precursor to form a positive thickness gradient stationary phase, which extends from an inlet to an outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. The second thickness is at least about 10% greater than the first thickness.

[0028] In one aspect, the interior surface of the chromatography column is silanized prior to introduction of the precursor liquid.

[0029] In one aspect, silanization comprises passing a reactive silane in a vapor phase through a column.

[0030] In one aspect, the chromatographic column comprises an inlet and an outlet, and introducing, and reacting or cross-linking comprises dynamically coating the interior surface of the chromatographic column by partially filling the chromatographic column with a precursor liquid, applying pressure at the inlet to force the precursor liquid down the length of the chromatographic column, and applying a vacuum at the outlet to evaporate the low boiling point solvent.

[0031] In one aspect, the first thickness is greater than or equal to about 10 nm to less than or equal to about 10 microns, and the second thickness is greater than or equal to about 30 nm to less than or equal to about 30 microns.

[0032] In one aspect, the second thickness is at least about 100% greater than or equal to the first thickness.

[0033] In one aspect, the second thickness is at least about 300% greater than or equal to the first thickness.

[0034] In one aspect, the chromatographic column is a micro gas chromatography column.

[0035] In one aspect, the stationary phase comprises a siloxane polymer.

[0036] In yet another aspect, the siloxane polymer includes at least one alkyl or aryl group comprising from 1 to 30 carbon atoms.

[0037] Further areas of applicability will become apparent from the description provided herein.The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0039] Figure 1An example embodiment of a gas chromatograph system is shown.

[0040] Figure 2 Shown is a cross-sectional view of a chromatography column having a stationary phase with a positive thickness gradient to enhance peak focusing according to certain aspects of the present disclosure.

[0041] Figure 3A-3C is a depiction of peak focusing by a film thickness gradient column (FTGC) according to certain aspects of the present disclosure. Figure 3A As shown, the thinner to thicker films focus the analyte peak as it travels along the column. Figure 3B is a diagrammatic representation of the setup used for column performance evaluation. Figure 3C It is a diagram of the forward operation mode and the backward operation mode.

[0042] Figure 4A-4C . Figure 4A is a diagram of the FTGC coating setup. The column was dynamically coated by partially filling with a plug of coating solution and then pushing the mixture out with a pressure of 5 psi. With the solution pushed out, a vacuum pressure of -2 psi was applied to the outlet to evaporate the solvent. Figure 4B This is a SEM image near the column inlet, and the film thickness is 34 nm. Figure 4C This is a SEM image near the column outlet, and the film thickness is 241 nm.

[0043] Figure 5A-5D . Figure 5A is to separate C7 to C in the forward operating mode 16 Diagram of a mixture of alkanes. Figure 5B Separate C7 to C in reverse or reverse operation mode with the same parameters 16 Diagram of a mixture of alkanes. Figure 5C Separate C7 to C in equal time backward mode 16 Diagram of a mixture of alkanes. Figure 5D The uniform thickness column is used to separate C7 to C 16 Diagram of a mixture of alkanes.

[0044] Figure 6 The diagram shows the 16 Resolution differences for alkanes between forward mode, same parameter mode and isochronous reverse / inverse mode and a column of uniform thickness.

[0045] Figure 7A-7D . Fig. 7A is a graph of the separation of a mixture of aromatic compounds in forward mode. Figure 7Bis a graph of a mixture of aromatic compounds separated within the same parameters. Figure 7C is a diagram of the separation of a mixture of aromatic compounds in the isochronous reverse / inverse model. Fig.7D is a graph of the separation of a mixture of aromatic compounds in a comparative column with a uniform column thickness. Peaks 1, 2, 3, 4, and 5 correspond to benzene, toluene, ethylbenzene, o-xylene, and 1,3-dichlorobenzene, respectively.

[0046] Figure 8 The difference in resolution between forward mode, same parameters mode and isochronous reverse mode and a column of uniform thickness is shown for the separation of aromatic compounds.

[0047] Figure 9A-9C . Fig.9A Figure 2 is a graph of the room temperature isothermal separation of C5 and C6 in the forward mode. Fig. 9B Figure 2 is a graph of the room temperature isothermal separation of C5 and C6 in reverse / inverse mode with the same parameters. Fig. 9C Figure 2 is a graph of the room temperature isothermal separation of C5 and C6 using a column of uniform thickness.

[0048] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0049] Example embodiments are provided so that the present disclosure will be thorough and will fully convey the scope to those skilled in the art. Many specific details, such as examples of specific compositions, components, devices, and methods, are set forth to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, and that the example embodiments may be embodied in many different forms and none should be construed as limiting the scope of the present disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known techniques are not described in detail.

[0050] The terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may also be intended to include plural forms unless the context clearly indicates otherwise. The terms "comprises, comprising", "including" and "having" are open, and therefore specifically refer to the presence of the features, elements, compositions, steps, integers, operations and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. Although the open term "comprising" should be understood as a non-limiting term for describing and requiring the various embodiments set forth herein, in some aspects, the term may be alternatively understood as a more restrictive and constraining term, such as "consisting of..." or "consisting essentially of..." Therefore, for any given embodiment that lists compositions, materials, components, elements, features, integers, operations and / or process steps, the present disclosure also specifically includes embodiments consisting of or essentially consisting of these listed compositions, materials, components, elements, features, integers, operations and / or process steps. In the case of “consisting of,” alternative embodiments exclude any additional compositions, materials, components, elements, features, integers, operations and / or process steps, while in the case of “consisting essentially of,” any additional ingredients, materials, components, elements, features, integers, operations and / or process steps that substantially affect the basic and novel properties are excluded from the embodiment, but any compositions, materials, components, elements, features, integers, operations and / or process steps that do not substantially affect the basic and novel properties may be included in the embodiment.

[0051] Unless specifically identified as an order of performance, the method steps, processes, and operations described herein should not be construed as necessarily requiring their performance in the particular order discussed or illustrated. It should also be understood that additional or alternative steps may be employed unless otherwise indicated.

[0052] When a component, element, or layer is referred to as being "on top of," "engaged to," "connected to," or "coupled to," the component, element, or layer may be directly on top of, engaged to, connected to, or coupled to, another component, element, or layer, or there may be intervening elements or layers. Conversely, when an element is referred to as being "directly on top of," "directly engaged to," "directly connected to," or "directly coupled to," there may be no intervening elements or layers. Other words used to describe relationships between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0053] Although the term first, second, third etc. can be used to describe various steps, elements, components, regions, layers and / or parts in this article, unless otherwise indicated, these steps, elements, components, regions, layers and / or parts should not be limited by these terms. These terms may only be used to distinguish a step, element, component, region, layer or part from another step, element, component, region, layer or part. Unless the context clearly indicates, otherwise when used in this article, terms such as "first", "second" and other numerical terms do not imply order or sequence. Therefore, without departing from the teaching of the example embodiment, the first step, element, component, region, layer or part discussed below can be referred to as the second step, element, component, region, layer or part.

[0054] Spatially relative terms or temporary relative terms, such as "before", "after", "inside", "outside", "under", "below", "below", "above", "above", etc., may be used herein for convenience of description to describe the relationship of one element or feature to another element or feature as shown in the figures. Spatially relative terms or temporary relative terms may be intended to encompass different orientations of a device or system in use or operation in addition to the orientation depicted in the figures.

[0055] Throughout this disclosure, numerical values ​​represent approximate measurements or limits to ranges to cover minor deviations from given values, embodiments having approximately the values ​​mentioned, and embodiments having exactly the values ​​mentioned. Except for the working examples provided at the end of the specific description, the numerical values ​​of all parameters in this specification (including the appended claims) (e.g., numerical values ​​of quantities or conditions) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. "About" means that the numerical value allows some slight imprecision (the accuracy of the value is approached by some method; approximately or reasonably close to the value; almost). If the imprecision provided by "about" is not understood in this ordinary sense in the art, then the "about" used herein at least represents the changes that may be produced by the ordinary methods of measuring and using these parameters. For example, "about" can include less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some aspects, optionally less than or equal to 0.1%.

[0056] Furthermore, disclosure of ranges includes disclosure of all values ​​and further divided ranges within the entire range, including the endpoints and sub-ranges given for the ranges.

[0057] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0058] In various aspects, the present teachings pertain to gas chromatography. Figure 1 As shown, a simplified illustration of a gas chromatography system 20 typically has at least five components: (1) a carrier gas source 22; (2) a sample injection system 24; (3) one or more gas chromatography columns 30; (4) a detector 32; and (5) a data processing system 34. The carrier gas introduced as the carrier gas source 22 (also called the mobile phase) is a high purity and relatively inert gas, such as helium, hydrogen, nitrogen, argon, or air. The carrier gas in a conventional system flows through the chromatography column 30 simultaneously with the sample fluid to be tested (throughout the separation process). The sample injection system 24 introduces a predetermined volume of a sample mixture including one or more target analytes to be tested (e.g., in gaseous form) into the chromatography column 30 by combining it with the flowing carrier gas from the carrier gas source 22. Thus, the carrier gas and the sample (which may have one or more target analytes) are introduced into the one or more chromatography columns 30. The sample moves through together with the co-injected carrier gas from the carrier gas source 22.

[0059] The target analyte species from the sample are separated and transported through the chromatography column 30, thereby eluting from the column. It should be noted that the eluted sample with one or more target analytes can be eluted from the chromatography column 30 in partial fractions, depending on the delay of the corresponding target analyte species as they pass through and are separated by the chromatography column 30. In addition, the sample fraction eluted from the chromatography column 30 can be optionally captured and re-injected downstream.

[0060] Typically, separation is achieved in chromatographic column 30 because the inner surface of the column is coated with (or the interior of the column is filled with) a material used as a stationary phase. The use of the term "column" is intended to broadly include various flow paths through which a fluid can flow, such as patterned flow fields from microfeatures defined in one or more substrates or other fluid flow paths recognized by those skilled in the art. The stationary phase adsorbs different target analytes in the sample mixture to varying degrees. The difference in adsorption causes different chemical species to delay when they travel down the chromatographic column and causes the difference in mobility in this way, thereby affecting the physical separation of target analytes in the sample mixture. In some variations, the chromatographic column is a micro gas chromatographic column. As used herein, "micro size" refers to a structure having at least one size of less than about 500 μm, optionally less than about 400 μm, optionally less than about 300 μm, optionally less than about 200 μm, optionally less than about 150 μm, and in some variations, a structure having a size optionally less than about 100 μm, which size can also cover nanoscale features. As used herein, reference to micro-size, microchannel, microfluidic channel or microstructure encompasses smaller structures, such as equivalent nanoscale structures. It should also be noted that while one dimension (such as diameter) may fall within the micro-size range, other dimensions (such as length) may exceed the micro-size range.

[0061] Various separated components are eluted from the chromatographic column 30 to enter one or more detectors 32 for analysis. Therefore, one or more detectors 32 are located at the end of one or more chromatographic columns 30. Therefore, the detector 32 is used to detect various chemical substances or target analytes in the sample appearing or eluting from the chromatographic column 30 at different times. Such detectors 32 are typically operated by destructive analysis of the eluted fractions in a gas chromatography system. Typical non-limiting examples of detectors 32 include mass spectrometers (mass spectrometers, MS) (e.g., time-of-flight mass spectrometers (time-of-flight massspectrometers, TOFMS)), flame ionization detectors (flame ionization detectors, FID), photoionization detectors (photoionization detectors, PID), electron capture detectors (electron capture detectors, ECD), thermal conductivity detectors (thermal conductivity detectors, TCD), etc. The data processing system 34 is typically also in communication with the detector 32 so that it is typically able to store, process and record separation test results.

[0062] In wall-coated capillary columns, retention of analytes is made possible by vapor interactions between the gas phase and the stationary phase coated on the capillary walls. As the analytes travel along the column, they encounter longitudinal and lateral mass transfer, which can lead to peak broadening, reduce GC resolution and increase the likelihood of co-elution. Typically, the correct choice of stationary phase within the column (to enable adequate analyte interaction and retention), the application of programmed temperature profiles, and split / splitless sample injection make it possible to improve chromatographic separation and resolution. However, in some cases, these methods are not sufficient to achieve the desired separation. For example, in portable GC, limited carrier gas supply prevents the use of split injection, while fine control of the temperature program is both difficult and limited by the power capacity of the system. In addition, even for specialized separations (e.g., separation of highly volatile compounds by porous layer open tubular columns), it may be difficult to completely separate all related compounds. Therefore, additional methods for improving column separations are desirable.

[0063] Negative temperature gradient separation (NTGS) is a method used to improve column performance by sharpening elution peaks. In NTGS, the column inlet is heated and a temperature gradient is generated via heat exchange with the surrounding environment. Due to the lower temperature towards the column outlet, the front of the peak travels slower than its tail, resulting in overall peak focusing. This effect can be optimized by adjusting different temperature profiles along the column, enabling high versatility under different conditions. However, due to the reliance of NTGS on heat exchange, focusing varies with ambient temperature, humidity, air convection rate, and thermal conductivity of the packing material, reducing repeatability and predictability (especially when complex temperature profiles are used). Complex thermal control modules can be used to stabilize the temperature gradient, but add additional size, weight, complexity, and cost to the GC device. In addition, the energy loss caused by the above-mentioned heat exchange is a relevant detriment for resource-limited systems (e.g., micro GC devices). In addition, the separation of highly volatile compounds usually requires close to ambient temperature, so the generation of temperature gradients will be avoided or minimized, thereby suppressing the NTGS effect. Therefore, despite being versatile and tunable, the use of NTGS for certain applications (e.g., portable GC) may be limited and challenging.

[0064] The present disclosure provides a novel method for peak focusing during gas chromatography. In certain aspects, a gas chromatography device for peak focusing of one or more target analytes includes a chromatographic column having an inlet and an outlet. The inlet receives a sample, which includes one or more target analytes that leave the chromatographic column at the outlet. The stationary phase is arranged and deposited in the chromatographic column and has a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. As will be further described below, wherein the second thickness is at least about 10% greater than the first thickness. In this way, the positive stationary phase thickness gradient is a gradient in which the stationary phase film thickness increases from the inlet toward the outlet. With the increase of the stationary phase thickness toward the outlet, the peak front moves slower than its tail, thereby focusing the overall peak.

[0065] Figure 2 An example of a chromatographic column 50 prepared according to certain aspects of the present disclosure that is capable of focusing peaks of one or more target analytes is shown. In certain aspects, the one or more target analytes may be volatile organic compounds (VOCs) that have relatively high vapor pressures and therefore low boiling points at the temperatures and pressures used within the chromatographic column 50. The VOC target analytes may include alkanes or aromatic compounds.

[0066] The chromatographic column 50 is defined by a wall 60. Thus, the wall 60 of the chromatographic column 50 can define a structure having a hollow interior region 52, which can be at least partially occupied by a stationary phase 64. The cross-sectional shape of the chromatographic column 50 can be selected from the group consisting of: circular, oval, rectangular, and triangular. In certain aspects, the chromatographic column 50 is formed of metal, silica or glass, or a polymer. The chromatographic column 50 defines an inlet 70 and an outlet 72. As shown in FIG. Figure 2 As shown, the wall 60 has a constant thickness. Thus, the first thickness of the wall 60 at the inlet 70, indicated by "T1", is the same as the second thickness of the wall 60 at the outlet 72, indicated by "T2".

[0067] As mentioned above, when the mixture of one or more target compounds in the sample / carrier mobile phase and the stationary phase 64 pass through the chromatographic column, the mixture interacts with the stationary phase.Each target analyte interacts with the stationary phase 64 to varying degrees or at different rates.The analyte that interacts least with the stationary phase 64 will first leave or elute from the chromatographic column 50.Usually, the target analyte that interacts most with the stationary phase 64 advances through the chromatographic column 50 at the slowest rate and therefore leaves last.By changing the characteristic of the mobile phase (carrier and sample) and the stationary phase 64, the different mixtures of the target analyte can be separated.As will be described below, the stationary phase 64 in the present technical context has a positive thickness gradient, which can focus the peak of one or more target analytes, which usually means that the analyte peak focuses as it advances to the outlet 72 from the inlet 70 of the chromatographic column 50.

[0068] In some variations, the stationary phase 64 may include silicon, such as silicon dioxide or a siloxane polymer. A variety of siloxane polymers may form the stationary phase 64. Typically, the siloxane polymer is a cross-linked polymer having a basic skeleton of silicon and oxygen, and side constituent groups that may be the same or different, typically consisting of a structural repeating unit (-O-SiRR'-) n Description, wherein R and R' can be the same or different side groups, and "n" can be any value greater than 2. Surface functionalization of silica or siloxanes can be performed in monomer or polymerization reactions with different short-chain organosilanes to react with silanol groups. Although the retention mechanism of the target analyte remains unchanged, the differences in the surface chemistry of different stationary phases can cause the selectivity for different target analytes to change. Siloxane polymers can include polyheterosiloxanes, in which the side groups or repeating units can be different. Examples of suitable side groups can be at least one unsubstituted or substituted alkyl or aryl group containing 1 to 30 carbon atoms, for example, including but not limited to: methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, phenyl, alkylphenyl, etc.

[0069] In various aspects, the stationary phase 64 is deposited on the inner surface 66 of the wall 60 and defines a positive thickness gradient. In certain variations, as will be further described below, the inner surface 66 can first be silanized, for example, by exposing the inner surface 66 to hexamethyldisilazane (HMDS) vapor to form a silane- or silanol-containing surface coating. Then, a precursor to a siloxane polymer (such as Silicone OV-1, a vinyl-modified 100% dimethylsiloxane commercially available as OV-1 6001 or Silicone OV-17 from Ohio Valley Specialty Company, a vinyl-modified 50% phenylsiloxane-50% methylsiloxane commercially available as OV-1 6017 from Ohio Valley Specialty Company) can be injected and reacted to form the stationary phase. A crosslinking agent (such as Dow SYLGARD TM 184 Reagent B (15% w / w, cross-linking agent)) may also be added with the precursor to promote cross-linking. Obviously, the stationary phase 64 is not limited to such materials, and these are provided merely as suitable examples for use in gas chromatography columns.

[0070] As shown, the stationary phase 64 extends from the inlet 70 to the outlet 72 along the inner surface 66 of the wall 60. The stationary phase 64 thus forms a continuous coating or film on the inner surface 66. The stationary phase 64 has a first thickness represented by "t1" at the inlet 70. The stationary phase 64 also defines a second thickness represented by "t2" at the outlet 72. The second thickness (t2) is at least about 10% greater than the first thickness (t1). Therefore, the stationary phase 64 defines a positive gradient thickness along the length of the chromatographic column 50. In this way, the inner region 52 has a first diameter (d1) defined by the first thickness "t1" of the stationary phase 64 at the inlet 70. The inner region 52 has a second diameter (d2) defined by the second thickness "t2" of the stationary phase 64 at the outlet 72. The first diameter (d1) is greater than the second diameter (d2). In this way, the stationary phase 64 defines a positive thickness gradient in the chromatographic column 50.

[0071] In certain aspects, the thickness gradient gradually increases between the first thickness (t1) and the second thickness (t2) along the length of the chromatography column 50. The thickness variation of the stationary phase 64 can be constant or vary along the length of the chromatography column 50, but the thickness increases from the inlet 70 to the outlet 72.

[0072] In certain variations, the second thickness (t2) is at least about 50% greater than the first thickness (t1), optionally at least about 100% greater than the first thickness (t1), optionally at least about 150% greater than the first thickness (t1), optionally at least about 200% greater than the first thickness (t1), optionally at least about 250% greater than the first thickness (t1), and in certain variations, the second thickness (t2) is at least about 300% greater than the first thickness (t1). The first thickness (t1) can optionally be greater than or equal to about 10 nm to less than or equal to about 10 microns, and the second thickness (t2) is greater than or equal to about 30 nm to less than or equal to about 30 microns. In one variation, the first thickness (t1) is about 30 nm and the second thickness (t2) is about 30 microns.

[0073] Figures 3A-3C is a description of peak focusing by employing a positive film thickness gradient (also referred to herein as a film thickness gradient column (FTGC)) according to certain aspects of the present disclosure. Figure 3A As shown, for a given analyte 80, the analyte peak 82 becomes increasingly focused as the analyte 80 travels down a chromatographic column 84 having a stationary phase 86 with a positive thickness gradient extending from an inlet 88 to an outlet 90 of the chromatographic column 84. Figure 3A As shown, as the analyte travels along the chromatographic column in the direction of the box arrow, the stationary phase 86 film thickness changes from thinner to thicker (in the direction from the inlet 88 to the outlet 90) in such a manner as to focus the analyte peak 82. Figure 3B is a diagrammatic representation of a setup for chromatographic column performance evaluation. The chromatographic column 84 is mounted in fluid communication with the injector 94 of an Agilent 6890 benchtop GC 96 equipped with a flame ionization detector (FID) 98 . Figure 3C is a diagram of a forward (top) mode of operation and a reverse / reverse (bottom) mode of operation. In other words, a sample containing at least two target analytes is introduced from inlet 88 in the forward mode (top) and travels in the direction of the box arrow toward outlet 90 of chromatography column 84. In reverse or reverse mode (bottom), a sample containing at least two target analytes is introduced to outlet 90 of chromatography column 84 and then travels in the direction of the box arrow toward inlet 88.

[0074] In certain aspects, the present disclosure contemplates a method for peak focusing in a gas chromatography device. The method may include introducing two or more target analytes into the inlet of a chromatographic column, the chromatographic column including a stationary phase deposited in the chromatographic column and having a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column. The second thickness is at least about 10% greater than the first thickness. The stationary phase may be any of the foregoing descriptions. The method includes separating two or more target analytes in a chromatographic column. In addition, the two or more target analytes are then eluted from the outlet of the chromatographic column.

[0075] In certain aspects, two or more target analytes are volatile organic compounds (VOCs). In one aspect, at least one of the two or more target analytes comprises an aromatic compound, and the total peak focus for the aromatic compound is greater than or equal to about 25%, for example, greater than or equal to about 26%, optionally greater than or equal to about 27%, and in certain variations, optionally greater than or equal to about 28%.

[0076] In another aspect, at least one of the two or more target analytes comprises an alkane compound, and the total peak focusing rate for the alkane compound is greater than or equal to about 10%, and in certain variations, optionally greater than or equal to about 11%.

[0077] On the other hand, the present disclosure contemplates a method for verifying peak focusing in a gas chromatography device. The method includes performing a forward operation by introducing two or more target analytes into the inlet of a chromatographic column, and the chromatographic column includes a stationary phase deposited in the chromatographic column and having a positive thickness gradient. The stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column, wherein the second thickness is at least about 10% greater than the first thickness. The stationary phase can have any design and composition described above. The forward operation includes separating two or more target analytes in the chromatographic column, and then eluting two or more target analytes from the outlet of the chromatographic column. Then, performing a reverse operation by introducing two or more target analytes into the outlet in the chromatographic column, the chromatographic column includes a stationary phase. Reverse operation also includes separating two or more target analytes in the chromatographic column and eluting two or more target analytes from the inlet of the chromatographic column. The method further includes comparing chromatographic resolution from the forward operation and the reverse operation, wherein the peak focusing rate of at least one pair of two corresponding peaks from two target analytes is greater than 5%, and optionally greater than or equal to about 10%.

[0078] The present disclosure also contemplates a method for manufacturing a gas chromatography device having a chromatographic column with a positive thickness gradient. The method includes introducing a precursor liquid into the chromatographic column. The precursor liquid includes a stationary phase precursor and a low boiling point solvent, which volatilizes along the length of the chromatographic column, thereby increasing the concentration of the stationary phase precursor when the stationary phase precursor moves along the chromatographic column and thus producing a stationary phase thickness gradient. The method also includes reacting or cross-linking the stationary phase precursor to form a positive thickness gradient stationary phase, which extends from an inlet to an outlet and has a first thickness at the chromatographic column inlet and a second thickness at the chromatographic column outlet. The second thickness is at least about 10% greater than the first thickness.

[0079] In some aspects, the inner surface of the chromatographic column is silanized before the precursor liquid is introduced. Silanization can include passing a reactive silane in the gas phase through the chromatographic column. In one embodiment, the reactive silane can be hexamethyldisilazane (HMDS) vapor, which forms a surface coating containing silane on the inner surface. In some variations, the reactive silane can be passed through the chromatographic column multiple times.

[0080] Then, a siloxane polymer precursor (such as Silicone OV-1, a vinyl-modified 100% dimethylsiloxane commercially available as OV-16001 or Silicone OV-17 from Ohio Valley Specialties, a vinyl-modified 50% phenylsiloxane-50% methylsiloxane commercially available as OV-1 6017 from Ohio Valley Specialties) can be injected and reacted to form a stationary phase. A crosslinking agent (such as Dow SYLGARD TM 184 Reagent B (15% w / w, cross-linker)) may also be added with the precursor to promote cross-linking. Obviously, the stationary phase is not limited to such materials and these are provided merely as suitable examples for gas chromatography columns.

[0081] The chromatographic column includes an inlet and an outlet, and the introduction and reaction (or cross-linking) can include dynamically coating the inner surface of the chromatographic column. This can be achieved by partially filling the chromatographic column with a precursor liquid, applying pressure at the inlet to force the precursor liquid down the length of the chromatographic column, and applying a vacuum at the outlet to evaporate the low boiling point solvent. For example, a precursor liquid plug can be pushed through the chromatographic column by applying a pressure of 5 psi at the inlet. A vacuum pressure of -2 psi can be applied to the outlet to evaporate the low boiling point solvent.

[0082] Example

[0083] Stationary phase thickness gradient gas chromatography (GC) columns can focus analyte peaks and improve separation resolution. Theoretical analysis and simulations show that focusing via a positive thickness gradient (i.e., stationary phase thickness) increases along the column. Peak focusing was experimentally demonstrated by coating a 5 m long capillary column with a film thickness varying from 34 nm at the column inlet to 241 nm at the column outlet. The column used C5 to C 16 Alkanes and aromatic compounds were analyzed in forward (thin to thick) mode and reverse (thick to thin) mode and compared with a uniform thickness column with a thickness of 131 nm.

[0084] Comparison of the resolution of the forward mode with that of the uniform thickness column showed an overall focusing efficiency (ie, improvement in peak capacity) of 11.7% for alkanes and 28.2% for aromatics.

[0085] The focusing effect was also demonstrated for isothermal separations of highly volatile compounds and for temperature-programmed separations with different heating rates. In all cases, the peak capacities from the forward mode separations were higher than those from the other modes, demonstrating the ability of the positive thickness gradient to focus the analyte peaks. Thus, as a general approach for improving GC separation performance, this thickness gradient technique can be widely applied to a variety of stationary phases and column types.

[0086] Test Setup

[0087] The FTGC was installed in a Figure 3B ) in an Agilent 6890 benchtop GC. Ultra-high purity helium was used as the carrier gas. Figure 3C As shown, the evaluation of the peak focusing effect was performed with the analyte injected from the thinner coating end (forward mode, i.e., traveling from thinner film to thinner film) or the thicker coating end (reverse mode, i.e., traveling from thicker film to thinner film). The uniform thickness column (film thickness is the same as the average thickness) was also evaluated using the same setup for comparison. All experiments were performed using a constant pressure temperature program. The temperature program method and pressure head are provided in Table 1.

[0088] Material

[0089] Analytical standard grade C5 to C 16 Benzene, toluene, ethylbenzene, o-xylene, 1,3-dichlorobenzene, nitrobenzene, and dichloromethane were purchased from Sigma-Aldrich (St. Louis, MO). Vinyl-modified OV-1 (P / N 6001) and OV-17 (P / N 6017) were purchased from Ohio Valley Specialties (Marietta, OH). Dow SYLGARD TM184 Reagent B was purchased from Ellsworth Adhesive (Germantown, WI). Deactivated fused silica tubing (P / N 10010, 250 μm ID) and RTX-5 columns (P / N 10205, 5 m length, 250 μm ID, 0.1 μm film thickness) were purchased from Restek (Berfonte, PA). DB-1MS columns (P / N 122-0162, 5 m length, 250 μm ID, 0.25 μm film thickness) were purchased from Agilent (Santa Clara, CA). All materials were used as purchased without further purification or modification.

[0090] Column Coating

[0091] OV-1 (75% w / w), OV-17 (10% w / w) and Dow SYLGARD TM 184 Reagent B (15% w / w, cross-linker) was dissolved in dichloromethane to generate a 2% (w / w) coating solution (effectively 5% phenyl stationary phase). A 5 m long capillary column (250 μm id) was silanized prior to coating by 8 repeated injections of hexamethyldisilazane (HMDS) vapor. Subsequently, 80 μL of the coating solution was loaded from the column inlet into the capillary 100 via a syringe pump ( Figure 4A ). A 5-psi positive pressure was applied from the inlet to drive the coating solution to the outlet. A negative 2-psi vacuum pressure 110 was applied to the outlet through a 1 m virtual column (250 μm i.d.), which ensured a constant coating plug speed. During coating, a small amount of low-boiling methylene chloride evaporated rapidly under vacuum, and as the coating solution plug moved from the column inlet to the outlet, the coating solution concentration gradually increased, and thus the film thickness increased. After coating, dry air flowed continuously through the column for 2 hours, and then crosslinked for an additional 2 hours at 80°C, followed by deactivation using HMDS. The column was then aged at 230°C for 3 hours at a helium flow rate of 0.5 mL / min. Using the same method, a column with a uniform thickness film was coated with a 1% (w / w) coating solution (same ingredients as above, but diluted), and a 5-psi positive pressure was applied from the inlet to drive the coating solution to the outlet (no vacuum was applied).

[0092] Simulation settings

[0093] C8 to C 15Simulations of the separation were performed in both forward and reverse modes and using a uniform thickness equivalent to the average gradient film thickness (separation conditions in Table 1). For a 5 m column, the film thickness varied from 34 nm to 241 nm (inlet to outlet for forward mode and outlet to inlet for reverse mode). It is worth noting that the calculation of the retention factor k(x,t) requires the value of the distribution coefficient K(t) (Eq. (2)), which was estimated based on the value in Ref.

[22] (see Section S3 - Simulation parameters and results in Supporting Information). Table 2 provides the simulated retention times and FWHMs, and Table 3 provides the resolutions.

[0094] Uniform thickness control

[0095] The Restek RTX-5 column was used for the separation of C7 to C16 alkanes in the forward mode and reverse mode as a control, and no difference in separation was expected. The separation conditions are provided in Table 1. The p-values ​​for retention time and FWHM (over 5 runs) were calculated using a paired "Student" t-test, and the resulting T-scores were converted to p-values. It was significant at p = 0.05; no significant differences were observed between the forward mode and the reverse mode for any analyte peak (see Section S4 - Control experiment using an a Restek RTX-5 column in Supporting Information). Similarly, for C7-C 15 For the HPLC-MS / MS, there was no significant difference between the forward and reverse modes when a 5 m long Agilent DB-1MS column was used (data not shown).

[0096] Stationary phase characterization

[0097] To characterize the thickness of the stationary phase, the FTGC was first frozen in liquid nitrogen and then several slices were cut. Scanning electron microscopy (SEM) images were taken near the column inlet (thinner films) and outlet (thicker films). Figure 2 (B) and (C) show that the film thickness increases from 34 nm to 241 nm from the inlet to the outlet, with a gradient of about 41 nm / m. Uniform thickness columns were also characterized at the inlet and outlet, with a film thickness of 131 nm at both ends of the column.

[0098] The theoretical explanation for peak focusing is as follows:

[0099] The effective velocity u of the analyte at position x (distance from the column inlet) is eff (x, t) and a given time t are started by:

[0100]

[0101] Among them, u M (x,t) is the velocity of the mobile phase, and k(x,t) is the retention factor:

[0102]

[0103] The distribution coefficient K(t) is defined as

[0104]

[0105] where R is the universal gas constant and T(x,t) is the time-dependent column temperature at position x. ΔG is the change in Gibbs free energy associated with the analyte moving from the stationary phase to the mobile phase and can be calculated from the change in analyte enthalpy (ΔH) and the change in analyte entropy (ΔS)

[0106] ΔG=ΔH-TΔS. (4)

[0107] The phase ratio β is defined by

[0108]

[0109] Among them, d i and d f (x) are the column inner diameter and film thickness, respectively. Therefore, equation (2) can be expressed as

[0110]

[0111] where A is a constant for a given column. The retention factor δk(x,t) that varies along the column can be written as (see the derivation in the Supplementary Information)

[0112]

[0113] Equation (7) shows that a slight increase in the retention factor δk / k along the column over a distance δx has two contributions: a negative temperature gradient given by the first term and a positive film thickness gradient given by the second term. This retention factor gradient (δk / k) is related to the velocity gradient in equation (1); thus, both the negative temperature gradient and the positive film thickness gradient result in a velocity difference between the front and tail of the band, thereby allowing the band to be focused (e.g., the spatial distribution of the analyte experiences a spatially varying velocity gradient). At the exit, this band is observed as a time-varying peak during elution that may be narrower than the corresponding peak from the unfocused band. In other words, peak focusing (an observable quantity) exists as a result of band focusing within the column. The equivalence of these two gradients can be expressed as

[0114]

[0115] Compared with traditional temperature gradient-based peak focusing, the film thickness gradient has several advantages. First, the film thickness gradient is independent of the column temperature, which allows focusing of any volatile analyte at any operating temperature. In particular, highly volatile compounds that are difficult to focus with NTGS can be focused according to the technology of the present invention (e.g., using FTGC chromatography devices and processes). Secondly, although the temperature gradient may vary with the heater and environmental conditions (such as heater arrangement, heat dissipation, column size / weight, column channel arrangement, and ambient temperature and airflow), the film thickness gradient is always constant and allows more reliable and repeatable GC operation (not easily affected by the environment). Finally, the FTGC according to certain aspects of the present disclosure can be used without additional accessories (such as heaters or coolers required for NTGS), which significantly reduces the complexity of the device for future integration. However, despite these advantages, in some aspects, separations based on film thickness gradients may not be as versatile as NTGS because the gradient is fixed, while the temperature gradient can be adjusted by changing the heat source and / or drain. In addition, the increased film thickness toward the column outlet may result in slow mass transfer, which may offset the peak focusing effect. The mass transfer effect is examined in the following simulations.

[0116] For this simulation, no temperature gradients (i.e., NTGS) were considered; only the film thickness gradient was analyzed. The time-dependent concentration c of the analyte peak traveling along the column was determined by solving the transient convection-diffusion equation

[0117]

[0118] Among them, u eff (x, t) is given in equation (1). The effective diffusion coefficient u eff (x, t) can be calculated from the local diffusion D and the retention factor k(x, t)

[0119]

[0120] d f as the film thickness, and D M is the mobile phase diffusion constant. It is worth noting that D includes both longitudinal and lateral mass transfer / diffusion. M (x,t) can be expressed as

[0121]

[0122] Diffusion constant D C (depending on the molar weights of the analyte and mobile phase molecules, and the atomic and structural diffusion volumes) and D S as the stationary phase diffusion constant. The local pressure p(x) is given by the inlet and outlet pressures p in and p out Sure

[0123]

[0124] L is the length of the column. u M is the velocity in the mobile phase, which is given by

[0125]

[0126] The viscosity η is given as the index α at temperature T0 and gas type n The following is a function of the viscosity η0:

[0127]

[0128] In equation (12), it is worth noting that the temperature T(x,t) is provided as T(t) assuming that the temperature along the column remains constant for a given time t. Equation (9) can be solved by applying the finite difference model to the discrete time (t) and position (i) vectors

[0129]

[0130] Δx and Δt are the simulation distance and time step. Combining these gives

[0131]

[0132]

[0133] The solution to equation (19) yields the time-dependent motion of the analyte peak along the column.

[0134] To simulate equation (19), several boundary conditions must be set. First, at t = 0, the injection peak has a Gaussian peak shape, i.e.

[0135]

[0136] where σ is the initial diffusion. Note that the initial peak at time t = 0 is located at x = 3σ. At the column inlet, after the initial injection, no additional analyte is injected into the column:

[0137] C(0,t)=0. (21)

[0138] At the column outlet, the final mesh concentration is approximately the same as the mesh concentration on the left (because it cannot be calculated by equation (16)), i.e.

[0139] C(L,t)=C(L-Δx,t). (22)

[0140] By observation, using equation (19), peak retention times and full widths at half maxima (FWHM) can be measured at the column outlet (i.e., x = L). The spatially varying concentrations are used to construct a two-dimensional matrix of concentrations that vary with position and time. For example, C8 to C 15 Compounds can be separated using positive (i.e., from thin to thick, or "forward" mode) and negative (i.e., from thick to thin, or "reverse" mode) film thickness gradients. Simulations of uniform thickness (thickness equal to the average forward / reverse mode film thickness) membranes were also performed as a control. The temperature was increased from 40°C to 240°C at a rate of 30°C / min. The head pressure was set to 3.45psi (the outlet was set to ambient pressure, i.e., 1 atmosphere). For a 5m column, the film thickness varied from 34nm to 241nm (from inlet to outlet for forward mode and from outlet to inlet for reverse mode). By observing the concentration along the second dimension (i.e., in time), a vector of concentration variation over time can be obtained, which corresponds to the signal obtained from the detector at the outlet. The maximum value (varying over time) corresponds to the elution / retention time, and the FWHM can be measured by observing the concentration at half the time of the peak. The resolution (R) between adjacent peaks can be additionally calculated using the formula

[0141]

[0142] where t1 and t2 are the retention times of the two peaks, and w1 and w2 are the corresponding FWHMs.

[0143] Peak retention time and full width at half maximum (FWHM) can be measured at the column outlet (ie, x = L) and are provided in Table 1. Table 1 shows the peak retention time and full width at half maximum (FWHM) for simulation, uniform thickness control, alkanes C7 to C 16 The programmed temperature profile and pressure head for the separation of hydrocarbons, separation of aromatic compounds, and separation of high volatility alkanes (C5 and C6).

[0144] Table 1

[0145]

[0146]

[0147] Table 2 shows the voltages used for C8 to C in forward and reverse modes. 15 The simulated retention time (RT) and full width at half maximum (FWHM) of . RT and FWHM for uniform coating thickness are also provided for reference. The temperature was increased from 40°C at a rate of 30°C / min and the pressure head was 3.45psi. The column length was 5m. All values ​​are provided in minutes. Other analyses are provided in Table 3.

[0148] Table 2

[0149] <![CDATA[RT fwd ]]> <![CDATA[FWHM fwd ]]> <![CDATA[RT uni ]]> <![CDATA[FWHM uni ]]> <![CDATA[RT bkwd ]]> <![CDATA[FWHM bkwd ]]> <![CDATA[C8]]> 0.460 0.0382 0.449 0.0519 0.439 0.0684 <![CDATA[C9]]> 0.731 0.0473 0.714 0.0704 0.697 0.0995 <![CDATA[C 10 ]]> 1.157 0.0574 1.136 0.0885 1.113 0.1296 <![CDATA[C 11 ]]> 1.639 0.0656 1.615 0.1005 1.560 0.1487 <![CDATA[C 12 ]]> 2.106 0.0713 2.082 0.1073 2.055 0.1584 <![CDATA[C 13 ]]> 2.591 0.0763 2.568 0.1120 2.541 0.1640 <![CDATA[C 14 ]]> 3.050 0.0807 3.027 0.1158 3.001 0.1679 <![CDATA[C 15 ]]> 3.460 0.0842 3.437 0.1186 3.411 0.1708

[0150] Table 3 shows the results for C8 to C in forward and reverse modes and in uniform thickness. 15 The simulated resolution (R) between adjacent peaks is shown in Figure 2. The forward mode resolution is greater than the reverse mode and uniform thickness resolution. The difference in resolution is defined as R diff =R fwd -R bkwd .

[0151] Table 3

[0152]

[0153]

[0154] Table 1 shows the analyte peaks eluted at different times in the forward mode and the reverse mode; this is because the separation conditions for a given analyte are different between the two modes. In the forward mode, the analyte is first exposed to a thinner film at low temperature and then reaches a thicker film at high temperature, which is exactly the opposite of what the analyte experiences in the reverse mode. Therefore, when evaluating column performance, the retention times for the analytes in the two modes are different and the full width at half maximum (FWHM) cannot be directly compared. Instead, the resolution R is used between the two peaks to analyze the separation performance (see Table 2), which is given by Equation 23.

[0155] Table 2 shows that the forward mode produces higher resolution between adjacent peaks when compared to the reverse mode, which means that the forward mode can contain more peaks than the reverse mode in the same time interval. The uniform thickness resolution is greater than the reverse mode resolution, but is always less than the forward mode resolution, thus indicating that peak focusing is achieved in the forward mode. Further analysis of the adjacent peak resolution shows that the difference in resolution between the forward mode and the reverse mode (i.e., R 差值 =R 正向 -R 逆向) decreases with increasing analyte retention. This is likely due to slower mass transfer (i.e., lateral diffusion) in the thicker film regions - this is more pronounced for heavier compounds. In forward mode, this effect causes lower volatility compounds to be wider closer to the column exit, thereby offsetting the focusing provided by the column. Conversely, in reverse mode, the thinner film at the exit results in less broadening, which offsets the defocusing from the reverse gradient. Thus, for lower volatility compounds, the resolution difference between forward and reverse modes is reduced.

[0156] Peak focusing of alkane mixtures. The peak focusing capability of FTGC is achieved by separating C7 to C 16 Alkane mixture was evaluated. 0.025 μL of liquid was used for injection with a split ratio of 5:1. The same separation conditions were used for forward mode, uniform thickness column, and reverse mode (denoted as “same parameters reverse mode”, see Table 1 – Alkane mixture). Example chromatograms are shown in Figures 5A-5D Shown in.

[0157] Figure 6 It is shown that for a uniform thickness column, the analyte peaks eluted at different times in the forward mode and the reverse mode with the same parameters are consistent with the simulation (Table 2). This is because the separation conditions of a given analyte are different between the two modes, which in turn are different from the uniform thickness column. In the forward mode, the analyte is first exposed to a thin film at low temperature, and then reaches a thicker film at high temperature, which is completely opposite to the experience of the analyte in the reverse mode. In a uniform thickness column, the analyte experiences the same film thickness at all temperatures. Therefore, when evaluating column performance, in these two modes and uniform columns, the retention time for the analyte is different, and the full width at half maximum (FWHM) cannot be directly compared. On the contrary, the resolution between adjacent peaks (e.g., C7 and C8, C8 and C9, etc.) is used to analyze the separation performance. The resolution of the reverse mode with the same parameters and the resolution of the uniform column are subtracted from the corresponding resolution in the forward mode; the resolution difference (i.e., R 正向 -R 相同参数逆向 or R 正向 -R 均匀 ) drawn on Figure 6The p-values ​​for the resolution differences were calculated using a paired "Student's" t-test (5 runs in forward mode and reverse mode with the same parameters as well as in uniform columns), and the resulting T-scores were converted to p-values ​​(see Table 3). It was significant at p = 0.05, indicating that the forward mode has significantly higher resolution between all pairs of adjacent peaks compared to the reverse mode with the same parameters. This was confirmed by simulations (Table 3), which also showed a higher resolution in the forward mode, meaning that the forward mode can contain more peaks than the reverse mode in the same time interval. The uniform thickness column resolution is lower than that of columns up to C 10 / C 11 Forward mode resolution, but for C 15 For the / C1 pair, the uniform resolution is higher. An overall performance analysis is provided below.

[0158] Table 4 shows the 16 p values ​​between forward mode and uniform thickness, reverse mode with identical parameter (IP), and reverse mode with equal time (ET) for alkane separation. Significant at p = 0.05. All p values ​​were significant between forward mode and reverse mode with IP, while for reverse mode with ET, C7 to C 13 The p-value of is significant. The significance of forward mode resolution is not reached until C 10 / C 11 When , they are all higher than the uniform thickness resolution, while for C 15 / C 16 For uniform thickness, the resolution is more significant.

[0159] Table 4

[0160]

[0161] To further explain the difference in retention times, a second set of chromatograms was obtained by reducing the reverse mode heating rate to ensure that C 16 (the last eluting analyte) eluted simultaneously with the forward mode (this is denoted as "isochronous reverse mode", see Table 1 - Separation Conditions, Figures 5A-5D Chromatogram, Figure 6 - resolution differences, Table 4 – p values). Similarly, the forward mode for C7 and C 13 The alkane pairs between the two provided significantly higher resolution (obtained from 5 runs), but the C 13 To C 16The performance is similar to that of the isochronous-reverse mode. Although the forward mode is not superior to the isochronous-reverse mode (or uniform thickness column) for all local resolution (i.e., between adjacent alkane pairs), the forward mode has a significantly higher peak capacity (PC), defined as the sum of all resolutions, compared to all other modes.

[0162] (Table 5). Focusing rate analysis, defined as

[0163]

[0164] This shows that the forward mode demonstrated an overall focusing efficiency of approximately 11.7%, 26.8% and 29.8% when compared to the uniform thickness column, the same parameter reverse mode and the isochronous reverse mode, respectively.

[0165] Table 5

[0166] Forward peak capacity 49.34±0.841 Reverse peak capacity (IP) 38.90±0.831 p-value 1.73e-4 Focusing rate (IP) 26.84％ Reverse peak capacity (ET) 38.02±2.400 p-value(ET) 4.62e-4 Focusing rate (ET) 29.76％ Average peak capacity 44.18±0.483 p-value (even) 1.63e-4 Focusing rate (uniform) 11.67％

[0167] Table 5. For Figure 5A-5D C7 to C 16 For the separation of alkanes, the peak capacity, total resolution, p-value and focusing ratio between forward mode, reverse mode with same parameters (IP), reverse mode with isochronous (ET), and with uniform thickness were significant at p = 0.05. The peak capacity in forward mode was significantly better than that in all other modes.

[0168] Peak focusing of aromatic compound mixtures

[0169] FTGC peak focusing was also used to analyze the separation of an aromatic mixture containing benzene, toluene, ethylbenzene, o-xylene, and 1,3-dichlorobenzene. 0.025 μL of the mixture was injected at a split ratio of 5:1 (separation conditions are provided in Table 1 – Aromatic mixture). Example chromatograms are shown in Figure 7A-7D is shown in , and the resolution difference is Figure 8 . The local resolution difference p-values ​​(calculated from 5 runs) are provided in Table 6. The peak capacity, p-values, and focusing rates are provided in Table 7, showing that the forward mode has a significantly higher peak capacity than all other modes. Therefore, whether the separation parameters are kept constant (and the analyte elutes faster in the reverse mode with the same parameters) or changed to ensure that the last compounds elute simultaneously (in the forward mode and the isochronous reverse mode), the separation performance in the forward mode is always better than any of the reverse modes. The forward mode is also better than the uniform thickness column, indicating a focusing rate of 28.2% (Table 7). Therefore, overall, the forward mode (i.e., positive film thickness gradient) demonstrates the ability to improve the separation peak capacity.

[0170] Table 6 shows the p-values ​​between the forward mode and the uniform thickness, identical parameter (IP) reverse mode and equal time (ET) reverse mode for aromatic separation. For elution order and abbreviations, see Fig. 7A – Fig.7D . Significant at p = 0.05. All p values ​​show significantly improved resolution in the forward mode.

[0171] Table 6

[0172] p-value p-value(IP) p-value(ET) p-value (even) B / T 3.08e-7 5.56e-7 1.83e-5 T / E 3.84e-7 9.28e-7 4.20e-6 E / X 9.32e-6 8.28e-5 0.012 X / DCB 5.95e-6 2.06e-5 2.28e-5

[0173] Table 7 shows the Figure 7A-7D Peak capacity, p-value and focusing ratio between forward mode, reverse mode with same parameters (IP) and reverse mode with isochronous (ET) and uniform thickness for separation of aromatic compounds in . Significant at p = 0.05. Separation in forward mode is significantly better than separation in all other modes.

[0174] Table 7

[0175] Forward peak capacity 13.47±0.089 Reverse peak capacity (IP) 9.59±0.060 p-value 1.60e-7 Focusing rate (IP) 40.35％ Reverse peak capacity (ET) 9.85±0.093 p-value(ET) 1.56e-6 Focusing rate (ET) 36.73％ Average peak capacity 10.50±0.146 p-value (even) 1.13e-5 Focusing rate (uniform) 28.22％

[0176] Warming effect

[0177] To show how the heating rate affects peak focusing, C7 to C500 nm with four different heating rates (0, 10, 20, and 30 °C / min, from 60 °C without hold) were performed in forward mode, reverse mode with the same parameters, and using a uniform thickness column. 10 The pressure was 3.45 psi (2.7 mL / min at 60 °C), and the split ratio for all separations was 15:1 (0.025 μL of mixed liquid was injected). The blank time was measured by methane injection and was found to be 0.36 minutes for all heating rates. The resolution and focusing rate for each temperature profile are provided in Table 8 (values ​​provided as the average of 5 runs). In forward mode, at higher heating rates, the analytes encounter relatively higher temperatures when they reach the thicker stationary phase closer to the column outlet. Therefore, the analytes spend less time in the thicker film, and peak broadening is also reduced. In reverse mode, the analytes first encounter the thicker stationary phase at a lower temperature and then flow to the thinner stationary phase at a higher temperature. The peak broadening from the low thickness stationary phase is already low; therefore, in reverse mode, the peak broadening due to increased temperature is generally reduced. Therefore, the focusing rate increases with increasing temperature ramp rate, reaching up to 61.9% compared to the forward and reverse modes and up to 68.1% compared to the forward mode and uniform thickness at a rate of 30°C / min.

[0178] Table 8 shows the resolution (R), peak capacity (PC), and focusing ratio for C7 to C10 separations in forward mode, reverse mode, and uniform thickness at different heating rates. The initial temperature used for all separations was 60°C and the carrier gas head pressure was 3.45 psi (2.7 mL / mi at 60°C). A split ratio of 15:1 was used to inject 0.025 μL of the mixed liquid.

[0179] Table 8

[0180]

[0181] For focusing of highly volatile compounds

[0182] Unlike NTGS, FTGC gradients are able to focus peaks at low temperatures where temperature gradients are difficult to generate (as long as the peaks are reasonably preserved at these temperatures). To demonstrate this, a room temperature isothermal separation of C5 and C6 was performed (Table 1) ( Figure 9A-9C ). The resolution, p-values, and focusing ratio (average of 5 runs) are provided in Table 9. The focusing ratio reached 40.2%, with an average forward mode resolution of 2.97 and a uniform thickness resolution of 2.12. It is worth noting for NTGS that it is difficult to achieve the same peak focusing effect for highly volatile compounds because only a small temperature gradient can be generated at the low operating temperature.

[0183] Table 9 shows the resolution, p-values ​​and focusing ratio for forward mode, reverse mode and uniform thickness for C5 and C6 separation at room temperature (26°C). Significant at p=0.05.

[0184] Table 9

[0185] Forward resolution 2.97±0.140 Reverse resolution 1.85±0.055 p-value (inverse) 1.17e-4 Focusing rate (reverse) 60.4％ Uniform resolution 2.12±0.049 p-value (even) 4.87e-4 Focusing rate (uniform) 40.2％

[0186] The development and evaluation of a stationary phase thickness gradient column technology capable of peak focusing is described in detail herein. The experimental results, confirmed by theoretical analysis and simulation, show an increase in the separation performance of various compounds in the forward mode, including the focusing separation of highly volatile compounds at room temperature. Compared with NTGS, FTGC has the advantages of a wider applicable temperature and compound volatility range, simple operation without auxiliary equipment, low dependence on environmental conditions, and better compactness. This stationary phase thickness gradient technology can be easily applied to a wide range of GC applications and can be used for stationary phases of any material or thickness as long as a gradient can be generated. In addition, it is applicable to capillary columns of regular circular cross-sections and also to microcolumns of rectangular cross-sections. For the purpose of illustration and description, the foregoing description of the embodiments has been provided. The description is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable and can be used in selected embodiments, even if not specifically shown or described, where applicable. The same part may also be varied in a variety of ways. These changes should not be considered as departing from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. A gas chromatography device for peak focusing of one or more target analytes, the gas chromatography device comprising: a chromatography column having an inlet and an outlet, wherein the inlet receives a sample including one or more target analytes that exits the chromatography column at the outlet; and A stationary phase is deposited within the chromatographic column and has a positive thickness gradient, wherein the stationary phase extends from the inlet to the outlet and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column, wherein the second thickness is at least 10% greater than the first thickness.

2. The gas chromatography apparatus according to claim 1, wherein: The first thickness is greater than or equal to 10 nm and less than or equal to 10 micrometers, and the second thickness is greater than or equal to 30 nm and less than or equal to 30 micrometers.

3. The gas chromatography apparatus according to claim 1, wherein: The second thickness is at least 100% greater than or equal to the first thickness.

4. The gas chromatography apparatus according to claim 1, wherein: The second thickness is at least 300% greater than or equal to the first thickness.

5. The gas chromatography apparatus according to claim 1, wherein: The chromatographic column is a micro gas chromatographic column.

6. The gas chromatography apparatus according to claim 1, wherein: The stationary phase comprises a siloxane polymer.

7. The gas chromatography apparatus according to claim 6, wherein: The siloxane polymer includes at least one alkyl group or aryl group, and the alkyl group or the aryl group includes 1 to 30 carbon atoms.

8. The gas chromatography apparatus according to claim 1, wherein: The cross-sectional shape of the chromatography column is selected from the group consisting of: circular, elliptical, rectangular and triangular.

9. A peak focusing method in a gas chromatography device, the method comprising: Introducing two or more target analytes into an inlet of a chromatography column, the chromatography column comprising: a stationary phase deposited inside the chromatography column and having a positive thickness gradient, wherein the stationary phase extends from the inlet to an outlet and has a first thickness at the inlet of the chromatography column and a second thickness at the outlet of the chromatography column, wherein the second thickness is at least 10% greater than the first thickness; separating the two or more target analytes in the chromatographic column; and The two or more target analytes are eluted from the outlet of the chromatography column.

10. The method according to claim 9, wherein: The two or more target analytes are volatile organic compounds (VOCs).

11. The method according to claim 9, wherein: At least one of the two or more target analytes includes an aromatic compound, and a total peak focusing rate for the aromatic compound is greater than or equal to 25%.

12. The method according to claim 9, wherein: At least one of the two or more target analytes includes an alkane compound, and a total peak focusing rate for the alkane compound is greater than or equal to 10%.

13. The method according to claim 9, wherein: The first thickness is greater than or equal to 10 nm and less than or equal to 10 micrometers, and the second thickness is greater than or equal to 30 nm and less than or equal to 30 micrometers.

14. The method according to claim 9, wherein: The second thickness is at least 300% greater than or equal to the first thickness.

15. The method according to claim 9, wherein: The chromatographic column is a micro gas chromatographic column.

16. The method according to claim 9, wherein: The stationary phase includes a siloxane polymer including at least one alkyl or aryl group, the alkyl or aryl group including 1 to 30 carbon atoms.

17. The method according to claim 9, wherein: The cross-sectional shape of the chromatography column is selected from the group consisting of: circular, elliptical, rectangular and triangular.

18. A method for verifying peak focusing in a gas chromatography apparatus, the method comprising: A forward operation is performed by introducing two or more target analytes into an inlet of a chromatography column, the chromatography column comprising: a stationary phase deposited inside the chromatography column and having a positive thickness gradient, wherein the stationary phase extends from the inlet to the outlet of the chromatography column and has a first thickness at the inlet of the chromatography column and a second thickness at the outlet of the chromatography column, wherein the second thickness is at least 10% greater than the first thickness; separating the two or more target analytes in the chromatographic column; eluting the two or more target analytes from the outlet of the chromatography column; performing a reverse operation by introducing the two or more target analytes into the outlet of the chromatography column, the chromatography column comprising a stationary phase; separating the two or more target analytes in the chromatographic column; eluting the two or more target analytes from the inlet of the chromatography column; and The chromatographic resolutions from the forward operation and the reverse operation are compared, wherein the peak focusing rate of at least one pair of two corresponding peaks from two target analytes is greater than 5%.

19. A method of manufacturing a gas chromatography device having a chromatography column, the chromatography column having a positive thickness gradient, the method comprising: introducing a precursor liquid into the chromatography column, wherein the precursor liquid comprises a stationary phase precursor and a low boiling point solvent, the low boiling point solvent volatilizing along the length of the chromatography column to increase the concentration of the stationary phase precursor as it moves along the chromatography column; and The stationary phase precursor is reacted or cross-linked to form the positive thickness gradient stationary phase, which extends from the inlet of the chromatographic column to the outlet of the chromatographic column and has a first thickness at the inlet of the chromatographic column and a second thickness at the outlet of the chromatographic column, wherein the second thickness is at least 10% greater than the first thickness.

20. The method according to claim 19, wherein: Prior to introducing the precursor liquid, the inner surface of the chromatography column is silanized.

21. The method according to claim 20, wherein: The silylation comprises passing a reactive silane in the gas phase through the chromatography column.

22. The method according to claim 19, wherein: The chromatographic column comprises an inlet and an outlet, and the introducing, and reacting or cross-linking comprises dynamically coating the interior surface of the chromatographic column by partially filling the chromatographic column with the precursor liquid, applying pressure at the inlet to force the precursor liquid down the length of the chromatographic column, and applying a vacuum at the outlet to evaporate the low boiling point solvent.

23. The method according to claim 19, wherein: The first thickness is greater than or equal to 10 nm and less than or equal to 10 micrometers, and the second thickness is greater than or equal to 30 nm and less than or equal to 30 micrometers.

24. The method according to claim 19, wherein: The second thickness is at least 100% greater than or equal to the first thickness.

25. The method of claim 19, wherein: The second thickness is at least 300% greater than or equal to the first thickness.

26. The method of claim 19, wherein: The chromatographic column is a micro gas chromatographic column.

27. The method of claim 19, wherein: The positive thickness gradient stationary phase comprises a siloxane polymer.

28. The method according to claim 27, wherein: The siloxane polymer includes at least one alkyl group or aryl group, and the alkyl group or the aryl group includes 1 to 30 carbon atoms.

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