METHOD FOR SEPARATION OF PRISTANE DIASTEROISOMERS

Abstract

The invention relates to a method for separating pristane diastereomers. A pristane sample is prepared and then injected into a chromatographic instrument equipped with a chiral chromatography column, where a stationary phase of the chiral chromatography column has a predefined pore size. The pristane diastereomers in the pristane sample are separated by the chiral chromatography column, and the components produced by the separation of the pristane diastereomers are sequentially fed into a mass spectrometer for detection and analysis.

Description

Title of the invention: PROCESS FOR THE SEPARATION OF PRISTANE DIASTEREOISOMERS Technical field

[0001] The present invention relates to instrumental analysis, in particular to a method for separating diastereoisomers of pristane. TECHNOLOGICAL BACKGROUND

[0002] Due to the lack of vitrinite in the very and overmature marine source rocks of the Lower Paleozoic in China, it is difficult to evaluate the maturity of the very and overmature source rocks in the current oil and gas exploration process.

[0003] As an isoprenoid alkane, pristane is a classic component of soluble organic matter in source rocks. It has been previously found that the pristane isomerization ratio can be used as a new index to identify the maturity of soluble organic matter in very and overmature source rocks, providing a new way to study the thermal maturity of very and overmature source rocks (Patience et al., 1978. The effect of maturation on the configuration of pristane in sediments and petroleum. Geochimica Et Cosmochimica Acta, 42(12):1871-1875; Patience et al., 1980. Acyclic isoprenoid alkanes and geochemical maturation. Physics & Chemistry of the Earth 12:287-293; and Wu et al., 2016.The geochemical characteristics of coals from the Junggar Basin, China, and relation of the configuration of pristane with maturity in highly mature and over mature samples. (OU & Gas Science and Technology, 71(35): 1-11). Unfortunately, there is still a lack of efficient and rapid separation and detection methods for pristane diastereomers. Conventionally, the separation is conducted using an ordinary chromatographic column, but the separation effect is not satisfactory with the maximum resolution of only 64% (Wu et al., 2016).The geochemical characteristics of coals from the Junggar Basin, China, and relation to the configuration of pristane with maturity in highly mature and over mature samples. OU & ​​Gas Science and Technology, 71 (35): 1-11). In addition, the separation must be controlled by different programs. temperature. At the same time, it takes at least 198 min to complete the separation and detection of a sample, leading to low efficiency. Due to the limitations of separation technology, the diastereoisomers of pristane cannot be sufficiently separated, so the isomerization ratio of pristane cannot be accurately calculated, leading to inaccurate assessment of the maturity of very and overmature source rocks.

[0004] SUMMARY

[0005] An objective of the present invention is to provide a method for separating pristane diastereoisomers to effectively improve the accuracy of assessing the maturity of very and overly mature source rocks.

[0006] The technical solutions of the present invention are described as follows:

[0007] The present invention relates to a process for separating diastereoisomers of pristane, characterized in that it comprises the operations consisting of: • prepare a sample of pristane; • injecting the pristane sample into a chromatographic instrument, the chromatographic instrument being equipped with a chiral chromatographic column; and subjecting the pristane diastereomers in the pristane sample to separation using the chiral chromatographic column; and • subjecting the components produced by the separation of pristane diastereoisomers sequentially to detection and analysis using a mass spectrometer.

[0008] In embodiments, the chiral chromatographic column is a [3-cyclodextrin] chiral chromatographic column.

[0009] In embodiments, the [3-cyclodextrin] chiral chromatographic column is an Rt-[3DEXcst] chiral chromatographic column.

[0010] In embodiments, the stationary phase of the chiral chromatographic column has a predefined pore size, in particular 0.5 nm -0.8 nm.

[0011] In embodiments, the pristane sample is prepared by a step of: • dissolve a pristane standard in an organic solvent to prepare the pristane sample with a concentration of 0.01 mg / mL - 0.1 mg / mL.

[0012] In embodiments, the chromatographic instrument is an Agilent 7890 gas chromatograph.

[0013] In embodiments, the separation of the pristane diastereoisomers in the pristane sample by the chiral chromatographic column is carried out under the following chromatographic conditions: • a carrier gas of the chromatographic instrument is helium with a constant flow rate of 0.8 mL / min; a temperature of an injection port of the chromatographic instrument is 280°C; a split ratio of the injection port of the chromatographic instrument is (10-50):1; and a heating program of the chiral chromatographic column is established as follows: initial temperature of 100°C for 5 min; rise to 120°C at a rate of 1°C / min; and 120°C for 20 min.

[0014] In embodiments, the mass spectrometer is a triple quadrupole (QQQ) mass spectrometer, such as 7000B.

[0015] In embodiments, the detection and analysis of the components produced by the separation of pristane diastereomers are performed under the following mass spectrometry (MS) conditions: • an ionization energy of the mass spectrometer is 70 eV; and a temperature of the ion source is 230°C; • components entering the mass spectrometer are collected by SCAN and MRM; and a scan mass range of SCAN and MRM is 80-300 atomic mass units (amu).

[0016] In embodiments, the chromatographic instrument is provided with a plurality of sample chambers; each of the different sample chambers is configured to receive a pristane sample; and the different sample chambers are each provided with the chiral chromatographic column for separating components of the pristane diastereomers in the pristane sample.

[0017] In embodiments, the mass spectrometer is provided with a plurality of detection chambers; the different detection chambers are in one-to-one correspondence with the different sample chambers; and the components produced by the separation in each of the different sample chambers sequentially enter a corresponding detection chamber to be detected and analyzed.

[0018] In particular, the invention relates to a process for the separation of diastereoisomers of pristane in isoprenoid hydrocarbons, characterized in that it comprises the operations consisting of: • prepare a standard sample of pristane with a concentration of 0.05 mg / mL; and • inject the standard pristane sample into a gas chromatograph equipped with a triple quadrupole mass spectrometer for GC / MS / MS analysis;

[0019] wherein an injection volume is 2 qL; a chromatographic column is a 30 mx 0.32 mm x 0.25 qm chiral chromatographic column; Individual components in the pristane standard sample are identified based on a characteristic ion and relative retention time of a corresponding reference standard and NIST library search results 11; a blank sample is injected between two adjacent sample injections;

[0020] The chromatographic conditions are listed as follows: • a carrier gas of the gas chromatograph is helium with a constant flow rate of 0.8 mL / min; a temperature of an injection port is 280°C; and a heating program of the chiral chromatographic column is established as follows: initial temperature of 100°C for 5 min.; rise to 120°C at 1°C / min.; and 120°C for 20 min.; and • the mass spectrometry conditions are as follows: • an ionization energy of 70 eV; an ion source temperature of 230°C; and • collection mode: full scan (SCAN) and multiple reaction monitoring (MRM); and a scan mass range: 80-300 amu.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] Unlike the prior art, the present application uses a chiral chromatographic column to separate the pristane diastereomers in the pristane sample. Since pristane contains chiral carbon atoms, the pristane diastereomers have different optical activities. The chiral column is provided with a chiral stationary phase, which is prepared by attaching an optically active monomer to silica gel or other polymers. Unlike ordinary chromatographic columns, the chiral chromatographic column creates a chiral environment to vary the pristane diastereomers in their physical properties, and thus achieve chiral recognition, so as to achieve the separation of the pristane diastereomers.In addition, the chiral chromatographic column proposed here has a predefined pore size, namely 0.5 nm - 0.8 nm, which allows the components produced by the separation of pristane diastereomers to pass through, facilitating the separation of pristane diastereomers. Brief description of the drawings

[0023] The present invention will be described in more detail hereinafter with reference to the accompanying drawings.

[0024] [Fig.l] shows the molecular structures of pristane isomers.

[0025] [Fig.2] illustrates the separation of pristane diastereoisomers in Huangxian coal gangue (HG) by the HP-5 chromatographic column (100 mx 0.25 mm x 0.25 pm) under thermal simulation at different temperatures, where the heating program of the chromatographic column is established as follows: initial temperature of 80°C for 1 min; rise to 130°C at a rate of 0.3°C / min; rise to 280°C at a rate of 5°C / min; and 280°C for 30 min.

[0026] [Fig.3] illustrates a separation of pristane diastereomers by a Rt-bDEXcst chiral chromatographic column (30 mx 0.32 mm x 0.25 pm), where the heating program of the chiral chromatographic column is set as follows: initial temperature of 100°C for 5 min.; rise to 120°C at 1.0°C / min.; and 120°C for 20 min.; the upper spectrum is the standard sample, and the lower spectrum is the Minqin oil shale.

[0027] DETAILED DESCRIPTION OF THE DISCLOSURE

[0028] The present invention relates to a process for separating diastereoisomers of pristane, which is carried out as follows

[0029] (S 100) A sample of pristane is prepared.

[0030] (S200) The pristane sample is introduced into a chromatographic instrument equipped with a chiral chromatographic column, where a stationary phase of the chiral chromatographic column has a predefined pore size, namely 0.5 nm - 0.8 nm. The pristane diastereomers in the pristane sample are separated by the chiral chromatographic column.

[0031] (S300) Components produced by the separation of pristane diastereoisomers sequentially enter a mass spectrometer for detection and analysis.

[0032] The molecular structures of pristane isomers are shown in [Fig.l]. In this embodiment, since pristane contains chiral carbon atoms, the pristane diastereomers have different optical activities. The chiral column is provided with a chiral stationary phase, which is prepared by attaching an optically active monomer to silica gel or other polymers. Unlike ordinary chromatographic columns, the chiral chromatographic column creates a chiral environment to vary the pristane diastereomers in physical characteristics, and thus achieve chiral recognition, so as to effect the separation of pristane diastereomers.In addition, the stationary phase of the chiral chromatographic column provided herein has a predefined pore size, namely 0.5 nm - 0.8 nm, which allows the components produced by the separation of pristane diastereomers to pass through, facilitating the separation of pristane diastereomers.

[0033] Specifically, in step (S 100), the pristane sample is prepared as follows:

[0034] (SI 10) A predefined amount of pristane standard is dissolved in an organic solvent to prepare the pristane sample with a concentration of 0.01 mg / mL -0.1 mg / mL.

[0035] In this embodiment, the pristane sample with a concentration of 0.01 mg / mL -0.1 mg / mL can directly enter the chromatographic instrument to be separated through a chiral [3-cyclodextrin] chromatographic column without being diluted.

[0036] In this embodiment, the organic solvent is n-hexane.

[0037] In one embodiment, the concentration of the prepared pristane sample is of 0.05 mg / mL.

[0038] In one embodiment, the pristane standard is commercially available pure pristane.

[0039] In one embodiment, the pore size of the stationary phase of the chiral chromatographic column is 0.5 nm - 0.8 nm. In one embodiment, the chiral chromatographic column is a [3-cyclodextrin] chiral chromatographic column.Since the molecular weight of pristane is 268, compared with the existing α-cyclodextrin chiral chromatographic column (the pore size of the α-cyclodextrin chiral chromatographic column is so small that only small molecule guest substances (such as monophenyl) can be included) and the γ-cyclodextrin chiral chromatographic column (the pore size of the γ-cyclodextrin chiral column is so large that it is only used for the inlet of large molecule terpenoids), the [3-cyclodextrin chiral chromatographic column provided herein is more preferred due to its moderate size, which is within the predefined range of 0.5-0.8 nm in this embodiment, allowing the pristane sample to pass through. Therefore, the γ-cyclodextrin chiral chromatographic column is more suitable for the separation of pristane diastereomers. .

[0040] Furthermore, the [3-cyclodextrin] chiral chromatographic column is an Rt-[3DEXcst] chiral chromatographic column, preferably a 30 mx 0.32 mm x 0.25 pm Rt-bDEXcst chiral chromatographic column (Agilent, USA).

[0041] Further, an injection volume of the pristane sample is 1 pL - 2 pL, preferably 2 pL.

[0042] Further, step (S200) is specifically performed as follows:

[0043] The pristane sample is vaporized, and then the pristane diastereomers in the vaporized pristane sample are separated by the chiral chromatographic column.

[0044] In addition, the chromatographic instrument is an Agilent 7890 gas chromatograph.

[0045] Furthermore, the mass spectrometer is a 7000B triple quadrupole mass spectrometer. The 7000B triple quadrupole mass spectrometer has a multi-reaction monitoring (MRM) scanning function and a high sensitivity (up to 10 fg), which can improve the detection of each component produced by the separation of the pristane sample, effectively improving the detection accuracy of trace components. Specifically, the mass spectrometer can be composed of other triple quadrupole mass spectrometers with the multi-reaction monitoring (MRM) scanning function.

[0046] In this embodiment, an Agilent 7890 gas chromatograph is coupled to a 7000B triple quadrupole mass spectrometer for GC-MS / MS analysis. The GC-MS / MS analysis has high sensitivity and strong anti-interference ability. The volume of a single injection is 2 pL. The column adopts a 30 mx 0.32 mm x 0.25 pm Rt-bDEXcst chiral column (Agilent, USA). The components of the pristane sample are identified according to the characteristic ions of the pristane sample, the relative retention time of each component in the chromatograph and mass spectrometer, and the search results of the NIST 11 library.

[0047] Further, the chromatographic conditions for the separation of pristane diastereomers in the pristane sample by the chiral chromatographic column are described as follows:

[0048] the carrier gas is helium with a constant flow rate of 0.8 mL / min; the temperature of an injection port of the chromatograph is 280°C; a split ratio of the injection port of the chromatograph is 10 - 50: 1; and the heating program of the chiral chromatographic column is set as follows: initial temperature of 100°C for 5 min.; rise to 120°C at a rate of 1°C / min.; and 120°C for 20 min.

[0049] In this embodiment, the carrier gas in the chromatograph is helium in a constant flow mode, so that the pristane sample can be transported by the helium at a certain flow rate into the chiral chromatographic column for separation, and then the various components produced by the separation are loaded into the mass spectrometer for detection and analysis. The helium gas only plays a role of transporting the pristane sample without participating in the separation, and moreover, the helium gas is chemically inert with the highest ionization energy among all gases, so that it is difficult to ionize, and will not affect the baseline of the chromatogram due to the air flow. unstable. More importantly, helium has a relative molecular mass of 4, and a high flow conductance, so that it is easy to separate from other molecular components, and has an enrichment effect on pristane samples.

[0050] Furthermore, the temperature of the injection port is set at 280°C to enable the pristane sample introduced into the chromatograph to be rapidly vaporized and then enter the chiral chromatographic column according to the preset splitting ratio, thereby realizing the separation of various components.

[0051] In embodiments, the split ratio of the injection port of the chromatograph is set to 10 - 50: 1, i.e., only 1 / 50 -1 / 10 of the vaporized pristane sample is allowed to enter the chiral chromatographic column for separation, which can effectively avoid overloading of the chiral chromatographic column.

[0052] In embodiments, the individual components produced by the separation of the pristane sample are detected and analyzed under the following mass spectrometry conditions: the ionization energy of the mass spectrometer is 70 eV; the temperature of the ion source is 230°C; and the mass spectrometer collects the components entering the mass spectrometer by SCAN and MRM with a mass range of 80-300 amu.

[0053] In this embodiment, two acquisition methods, SCAN and MRM, are used to simultaneously analyze the components produced by the separation of the pristane sample. SCAN is used to determine the components that are less affected by impurities and have sufficient sensitivity in the SCAN mode. In this case, the target components to be determined by MRM are minimized, which can minimize the pre-established processing of MRM analysis conditions.

[0054] In embodiments, the chromatographic instrument is provided with a plurality of sample chambers, and each sample chamber is configured to receive a pristane sample. In addition, each sample chamber is provided with a corresponding chiral chromatographic column for separating pristane diastereomer components in the pristane sample. Furthermore, the mass spectrometer is provided with a plurality of detection chambers, which are in one-to-one correspondence with the sample chambers; and the individual components produced by the separation in each sample chamber sequentially enter the corresponding detection chamber for detection and analysis. In this way, multiple samples can be separated, detected, and analyzed at the same time, thereby improving efficiency.

[0055] The pristane diastereomers in a real source rock (Minqin oil shale) are analyzed by the method proposed herein under the following chromatographic conditions: the chiral chromatographic column is an Rt-bDEXcst chiral chromatographic column (30 mx 0.32 mm x 0.25 pm); and the heating program of the chiral chromatographic column is set as follows: initial temperature 100°C for 5 min.; ramping to 120°C at 1.0°C / min; 120°C for 20 min. The resolution of the pristane diastereomers is calculated. The chromatogram is shown in [Fig.3], and the resolution is shown in Table 1. Table 1 also shows the separation parameters of the pristane diastereomers in the pristane sample.

[0056] Table 1 - Chromatography parameters for separation

[0057] of diastereoisomers of pristane Sample Chromatographic column type Initial temperature °C Final temperature °C Heating rate 0° C / min Resolution % Minqin oil shale Rt-bDEXcst 30m x 0.32mm x 0.25pm ​​100 120 1 93

[0058] It can be seen from [Fig.3] that the method proposed here improves the degree of separation of isoprenoid diastereomers, and achieves almost complete separation of pristane diastereomers, with a resolution of 93%.

[0059] By combining the Rt-bDEXcst chiral chromatographic column (30 mx 0.32 mm x 0.25 pm, Agilent, USA) with GC-MS(QQQ) / MS, the complete separation of pristane diastereomers is almost achieved under certain conditions, which ensures the accuracy of calculating the biological and geological pristane diastereomer ratio, and solves the problem that the maturity of highly and overly mature marine source rocks cannot be determined due to the lack of vitrinite, providing technical support for deep and ultra-deep marine oil and gas exploration. At the same time, the method of the present invention can also be fully applied to the maturity identification of conventional vitrinite-containing source rock, and can avoid counting errors caused by manual operation in the method of counting the number of vitrinites under a microscope.Therefore, the pristane isomerization ratio not only can be used as a new indicator to determine the thermal maturity of highly and overly mature marine crude oil source rocks, but also can provide an alternative way to determine the maturity of conventional continental source rocks.

[0060] At the same time, the present invention improves the resolution of pristane diastereomers, and achieves the almost complete separation of pristane diastereomers, with a resolution of 93% (as shown in [Fig.3] and Table 1). The method presented here has the following advantages: 1. It can be fully applied to the determination of maturity of very and over-mature marine source rocks and the research of oil-source rock correlation. 2. This method has a simple operation, in which the sample does not need to be specially treated.

[0061] (3) This method facilitates the improvement of the accuracy of the determination of the source rock maturity. Specifically, compared with the HP-5 chromatographic column (100 mx 0.25 mm x 0.25 pm) used in [Fig. 2], the Rt-bDEXcst chiral chromatographic column (30 mx 0.32 mm x 0.25 pm) used in [Fig. 3] provides higher resolution, so that the ratio of pristane diastereomers can be calculated accurately, and the source rock maturity can be identified more accurately, thereby overcoming the difficulty in determining the maturity of very and overmature marine source rocks. Table 2 shows the resolution (R) of pristane diastereomers under different heating rates using different types of chromatographic columns.

[0062] Table 2 - Resolution (R) of pristane diastereoisomers under different heating rates using different types of chromatographic columns Chromatographic column type and resolution (R, %) Heating rate 3°C / min Heating rate 2°C / min Heating rate 1°C / min Heating rate 0.5°C / min Heating rate 0.3°C / min HP-5 (100m) Rt-bDEXcst (30m) 21 56 93 16 64

[0063] Note: Resolution (R = 100% hi / h2); where hi is the distance between the top of the SS+RR peak in pristane diastereomers and the intersection of the RS peak and the SS+RR peak; h2 is the peak height of the SS+RR peak in pristane diastereomers; and "-" means inseparable. 1. The method improves the analysis speed and shortens the analysis time.

[0064] Specifically, compared with the conventional 100 m HP-5 chromatographic column, the 30 m Rt-bDEXcst chiral chromatographic column adopted herein greatly shortens the analysis time, saves the cost and greatly improves the processing efficiency. The heating rate of the 30 m Rt-bDEXcst chiral column is 1°C / min, and the time required is only 45 minutes, while the heating rate of the 100m HP-5 column is 0.3°C / min, and the time required is as long as 198 minutes.

Claims

[Claim 1] Claims - Process for the separation of diastereoisomers of pristane in isoprenoid hydrocarbons, characterized in that it comprises: • prepare a standard sample of pristane with a concentration of 0.05 mg / mL; and • inject the standard pristane sample into a gas chromatograph equipped with a 7000B triple quadrupole mass spectrometer for GC / MS / MS analysis; wherein an injection volume is 2 qL; a chromatographic column is a 30 m x 0.32 mm x 0.25 qm Rt-[SDEXcst] chiral chromatographic column; individual components in the pristane standard sample are identified according to a characteristic ion and relative retention time of a corresponding reference standard and NIST library search results 11; a blank sample is injected between two adjacent sample injections; The chromatographic conditions are listed as follows: • a carrier gas of the gas chromatograph is helium with a constant flow rate of 0.8 mL / min; a temperature of an injection port is 280°C; and a heating program of the chiral chromatographic column Rt-[3DEXcst is established as follows: initial temperature of 100°C for 5 min.; rise to 120°C at 1°C / min.; and 120°C for 20 min.; and • the mass spectrometry conditions are as follows: • an ionization energy of 70 eV; an ion source temperature of 230°C; and • collection mode: full scan (SCAN) and multiple reaction monitoring (MRM); and a scan mass range: 80-300 amu.

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