Method for preparing 4-methyl-2-pentanone standard for GC

Abstract

This invention discloses a method for preparing 4-methyl-2-pentanone standards for GC, specifically relating to the field of gas chromatography analysis technology. The method specifically includes preparation methods for gas chromatography analytical standards of three types of analytes: solid, liquid, and gas. Liquid analytes are enriched using a Fe3O4@MOF-5@GO magnetic composite material, combined with microwave-assisted BSTFA derivatization and deuterated internal standard correction. Gaseous analytes are extracted using a needle extraction device filled with an ionic liquid-modified graphitized carbon black / carbon molecular sieve composite adsorbent, achieving efficient BTEX enrichment and online internal standard correction. Solid analytes are analyzed using a Fe3O4@ZIF-8@MWCNTs@GO-NH₂ multi-level core-shell composite material, achieving simultaneous analysis of inorganic salts and organic acids through stepwise elution and stepwise derivatization. This method features high enrichment fold, low detection limit, and high recovery rate, and is suitable for simultaneous qualitative and quantitative analysis of multiple target analytes in complex samples.

Description

Technical Field

[0001] This invention relates to the field of gas chromatography analysis / technology, and to a method for preparing 4-methyl-2-pentanone standards for GC. Background Technology

[0002] In gas chromatography (GC) analysis, the preparation of standard reference materials is crucial for ensuring the accuracy, comparability, and traceability of analytical results. However, existing methods for preparing standards for liquid analytes mostly employ traditional liquid-liquid extraction or solid-phase extraction techniques, which suffer from low enrichment efficiency and poor selectivity, making it difficult to achieve efficient enrichment of trace targets in complex matrices. Furthermore, compounds with significant polarity differences in liquid samples often exhibit poor reproducibility during derivatization due to the difficulty in controlling reaction conditions, thus affecting the stability and accuracy of quantitative results. The lack of efficient enrichment materials and standardized derivatization processes for liquid samples in traditional methods has become a significant bottleneck restricting the improvement of sensitivity and precision in GC analysis.

[0003] For gaseous test samples, the preparation of traditional standards often relies on static gas mixing in gas cylinders or storage in high-pressure gas tanks. This method suffers from drawbacks such as bulky equipment, inconvenience in carrying, high storage pressure, and susceptibility of gas concentration to temperature and pressure changes. Particularly in on-site sampling and rapid detection scenarios, the transportation and use of traditional gaseous standards are extremely inconvenient, and it is difficult to guarantee long-term concentration stability. Furthermore, traditional methods lack effective internal standard correction mechanisms during the enrichment and introduction of gaseous standards, making them prone to quantitative deviations due to fluctuations in sampling volume, adsorption efficiency, or injection conditions. This limits their application and promotion in fields such as environmental monitoring and occupational health testing.

[0004] In the preparation of gas chromatographic standards for solid analytes, traditional methods typically employ simple solvent extraction or ultrasonic extraction, lacking specific enrichment and separation techniques for target analytes with different physicochemical properties. Especially for complex solid samples containing both inorganic salts and organic acids, existing methods struggle to achieve simultaneous extraction and derivatization of multiple target analytes, resulting in low recoveries, high detection limits, and poor reproducibility. Furthermore, due to the lack of suitable internal standards to correct systematic errors in sample pretreatment and instrument analysis, quantitative analysis of traditional solid standards often suffers from significant matrix interference and signal drift, failing to meet the requirements of high-precision analysis. Summary of the Invention

[0005] To overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a method for preparing 4-methyl-2-pentanone standard for GC, which solves the technical problems existing in the preparation methods of gas chromatography analysis standards, such as low enrichment efficiency, poor derivatization reproducibility, inconvenience of carrying gaseous standards and easy concentration changes, and poor quantitative accuracy due to lack of internal standard correction.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The method for preparing GC standard using 4-methyl-2-pentanone specifically includes the following steps: Specifically, this includes methods for preparing gas chromatographic analysis standards for solid test substances, methods for preparing gas chromatographic analysis standards for liquid test substances, and methods for preparing gas chromatographic analysis standards for gas test substances.

[0007] Preferably, the method for preparing the gas chromatographic analytical standard of the liquid test substance specifically includes: A1: Take 80-100 parts by weight of magnetic Fe3O4 nanoparticles, then add 25-50 parts by weight of MOF-5 organic framework material to obtain Fe3O4@MOF-5 by solvothermal method, then add 25-50 parts by weight of graphene oxide GO and ultrasonically disperse at a frequency of 60kHz for 15-30min to prepare magnetic metal-organic framework / graphene composite material Fe3O4@MOF-5@GO; A2: Take 10-20 parts by weight of Fe3O4@MOF-5@GO and disperse it in 25-50 parts by weight of water / organic diluent containing the target analyte. Then add 1-2 parts by weight of anhydrous sodium sulfate and 0.5-1 parts by weight of sodium chloride and shake for 15 minutes. A3: Separate the magnetic adsorbent from the final mixture obtained in A2 using an external magnetic field, discard the supernatant, and then wash the adsorbent with 5-8 parts by weight of 5% methanol aqueous solution and 5-8 parts by weight of ultrapure water in sequence to remove weakly bound impurities and salts. Repeat the washing twice and then dry under nitrogen flow at room temperature for 5 minutes. A4: Add 2-3 parts by weight of a mixed solvent of acetonitrile:ethyl acetate = 1:1 to the dried adsorbent in A3 and sonicate for 5 minutes. Then collect the eluent by magnetic separation. Elute the residual adsorbent with 2-3 parts by weight of acetonitrile solution containing 0.2% formic acid for 5 minutes by sonication. Combine the two eluents. A5: The last eluent from A4 was dehydrated by passing it through an anhydrous sodium sulfate column, and then the dehydrated eluent was dried in a water bath at 40°C with pure nitrogen. A6: Add 0.05-0.1 parts by weight of BSTFA containing 1% TMCS and 0.05-0.1 parts by weight of acetonitrile to the residue. After sealing, place the mixture in a microwave reactor and irradiate it at 300 W power and 70°C for 3 minutes. After cooling to room temperature, add 0.10-0.2 parts by weight of deuterated toluene-d8 containing 10 μg / mL and deuterated phenol-d6 containing 10 μg / mL to obtain the gas chromatographic analysis standard.

[0008] Preferably, the MOF-5 organic framework material in A1 has a microporous crystal structure, which is formed by the coordination self-assembly of terephthalic acid and zinc ions, and has a three-dimensional cubic network topology with a pore size of 0.8~1.2 nm.

[0009] Preferably, in A1, Fe3O4@MOF-5@GO has a core-shell structure with magnetic Fe3O4 nanoparticles as the core, a MOF-5 layer as the middle layer, and graphene oxide (GO) as the outer layer.

[0010] Preferably, the method for preparing the gaseous test sample gas chromatographic analysis standard specifically includes: B1: Graphitized carbon black and carbon molecular sieve are mixed evenly at a mass ratio of 2:1 to obtain an adsorbent. Then, 30-40 parts by weight of the adsorbent are taken and 5 wt% of [BMIM]PF6 ionic liquid is added to it and ultrasonically impregnated for 30 minutes. After the solvent has completely evaporated, the liquid is evenly coated on the surface of the adsorbent. B2: The modified adsorbent is filled into the middle of a stainless steel hollow needle. The filled needle extraction device is placed in an aging furnace at 250°C and aged for 4 hours with high-purity nitrogen gas introduced at a rate of 50 mL / min to obtain a composite adsorbent needle extraction device. B3: Inject 0.1~0.2 parts by weight of a methanol solution of toluene-d8 with a concentration of 100 ng / μL into the needle extraction device and purge with nitrogen for 2 minutes; B4: Using a dynamic gas mixing system, benzene, toluene, ethylbenzene, and o-xylene standard solutions are injected into the vaporization chamber to prepare a BTEX mixed standard gas with a concentration of 10 ppb. The needle extraction device prepared in B2 is connected to the gas sampling pump, the BTEX mixed standard gas is introduced and the flow rate is controlled at 100 mL / min, and then the standard gas is drawn off at a flow rate of 50 mL / min. B5: Remove the enriched needle extraction device and immediately insert it into a gas chromatograph with an injection port temperature of 250℃. At the same time, start the programmed temperature rise thermal desorption, set the initial injection port temperature to 50℃, and rapidly heat it to 250℃ at a rate of 10℃ / s and hold it for 2 minutes. The desorbed target analytes are carried by high-purity helium carrier gas and directly enter the chromatographic column for separation.

[0011] Preferably, the graphitized carbon black in B1 is a layered or flocculent aggregate of graphite microcrystals, formed by high-temperature graphitization of carbon black, with a spacing of 0.335~0.340 nm between the graphite microcrystals.

[0012] Preferably, the carbon molecular sieve in B1 is a microporous carbonaceous adsorbent material with a regular slit-like or columnar pore structure and a pore size distribution concentrated in the range of 0.4 to 0.7 nm.

[0013] Preferably, the method for preparing the solid test substance gas chromatographic analysis standard specifically includes: C1: Weigh 80-100 parts by weight of Fe3O4 nanoparticles and 25-50 parts by weight of ZIF-8 metal-organic framework material, and then prepare Fe3O4@ZIF-8 by solvothermal method. Then, load 25-50 parts by weight of multi-walled carbon nanotubes and 25-50 parts by weight of aminated graphene oxide through electrostatic self-assembly to prepare multifunctional magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2. C2: Weigh 1-2 parts by weight of solid sample, grind it and place it in a centrifuge tube. Then add 8-10 parts by weight of methanol:water = 1:1 extraction solution and shake and stir for 5 minutes. Then extract with ultrasound at 50 kHz frequency for 15 minutes. Finally add 10-20 parts by weight of the magnetic composite material prepared in C1 and continue to shake for 20 minutes. C3: The magnetic adsorbent obtained in C2 is separated by an external magnetic field. The supernatant is then discarded. The adsorbent is then washed with 5-8 parts by weight of ultrapure water, 5-8 parts by weight of 5% methanol aqueous solution, and 5-8 parts by weight of n-hexane in sequence. Finally, it is dried with nitrogen at room temperature of 25°C for 5 minutes. C4: Add 2-5 parts by weight of acetonitrile solution containing 0.5% triethylamine to the adsorbent, then elute with ultrasound at 50kHz for 5 minutes, collect eluent A by magnetic separation, and add 2-5 parts by weight of acetonitrile solution containing 0.1mol / L acetylacetone to the residual adsorbent, elute with ultrasound for 5 minutes, and collect eluent B. C5: Eluent A collected in C4 was dried under nitrogen at 40°C. Then, 0.05-0.1 parts by weight of BSTFA containing 1% TMCS and 0.05-0.1 parts by weight of acetonitrile were added sequentially. After sealing, the eluent was heated to 80°C and kept at that temperature for 30 minutes. Eluent B was dried under nitrogen at 40°C. Then, 0.05-0.1 parts by weight of trifluoroacetylacetone, 0.05-0.1 parts by weight of acetonitrile and 0.10-0.20 parts by weight of pyridine were added as catalysts. After sealing, the eluent was heated to 60°C and kept at that temperature for 20 minutes to obtain the chelated derivative. C6: Combine eluent A and eluent B obtained from the chelated derivative in C5, then add 0.10~0.20 parts by weight of an internal standard mixed solution containing 10 μg / mL deuterated benzoic acid-d5 and 10 μg / mL deuterated naphthalene-d8, and finally pass it through a 0.22 μm filter membrane to obtain a gas chromatographic analytical standard.

[0014] Preferably, the multi-walled carbon nanotubes in C1 are hollow tubular structures with a diameter of 10-30 nm and a length of 5-15 μm, and the aminated graphene oxide in C1 is a sheet structure with a sheet thickness of 1-3 nm and amino functional groups grafted onto its surface.

[0015] Preferably, the magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2 in C1 has a multi-level core-shell structure, with Fe3O4 magnetic nanoparticles as the core, ZIF-8 as the middle layer, multi-walled carbon nanotubes forming a three-dimensional conductive network running through it, and aminated graphene oxide as the outer coating layer, forming a composite microsphere structure that combines magnetism, porous adsorption and surface functionalization.

[0016] The technical effects and advantages of the method for preparing 4-methyl-2-pentanone standard for GC of the present invention are as follows: 1. In this invention, Fe3O4@SiO2 is used as an adsorbent for liquid phase test samples. It has a large specific surface area and magnetic saturation. Compared with traditional solid phase extraction columns, the magnetic particles are uniformly dispersed in the sample, with an extraction efficiency of more than 70%. The magnetic particles can increase the enrichment amount and reduce the detection limit of trace compounds by 5 times.

[0017] 2. In this invention, the addition of derivatization reagents to liquid test samples significantly improves derivatization efficiency compared to traditional methods, and the relative standard deviation of derivatization reproducibility is significantly reduced from 15% to 5%.

[0018] 3. This invention utilizes an ionic liquid-modified graphitized carbon black / carbon molecular sieve composite adsorbent to fill a needle extraction device, achieving highly efficient enrichment of benzene compounds. The enrichment efficiency reaches 94.9%–97.8%, the humidity-affected rate is less than 3.6%, the internal standard correction deviation is less than 2.9%, and the thermal desorption recovery rate is above 92.1%. This method solves the problems of inconvenient portability, high storage pressure, and easily changing concentrations associated with traditional gaseous standard cylinders, offering advantages such as convenient operation and environmental friendliness.

[0019] 4. This invention introduces an online internal standard calibration technique into the preparation method of gaseous test samples. By pre-injecting the internal standard into the needle extraction device, systematic errors in the sampling, enrichment and thermal desorption processes are effectively eliminated, significantly improving the accuracy and reproducibility of quantitative analysis.

[0020] 5. In this invention, the solid test sample adopts a multifunctional magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2 with a multilevel core-shell structure. Through the coordination of ZIF-8, the hydrophobic adsorption of carbon nanotubes, and the electrostatic and hydrogen bonding of aminated graphene oxide, the simultaneous enrichment of inorganic salts and organic acid compounds is achieved, with an enrichment factor of 76 to 98 times and a detection limit as low as 0.05 to 0.35 μg / g.

[0021] 6. The present invention employs a stepwise elution and stepwise derivatization strategy in the preparation method of solid test samples. For inorganic ions and organic acids, acetylacetone chelation derivatization and BSTFA silanization derivatization are used respectively, which solves the technical problem of simultaneous analysis of multiple types of target substances in complex matrices. The recovery rate reaches 78.5% to 94.7%, and the RSD is less than 7.6%.

[0022] 7. This invention introduces a dual internal standard system of deuterated benzoic acid-d5 and deuterated naphthalene-d8 into the solid sample, which effectively corrects the matrix effect and signal drift during sample pretreatment and instrument analysis, significantly improving the accuracy and precision of quantitative analysis. It is suitable for simultaneous qualitative and quantitative analysis of multiple target substances in complex solid samples. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing liquid gas chromatography analytical standards proposed in this invention; Figure 2 This is a flowchart of a method for preparing gaseous gas chromatography analytical standards proposed in this invention; Figure 3 This is a flowchart of a method for preparing solid gas chromatography analytical standards proposed in this invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0026] Example

[0027] This embodiment provides a method for preparing 4-methyl-2-pentanone standard for GC, the specific implementation steps of which include: Experimental materials: Fe3O4@SiO2 particles, toluene, MPS (3-methacryloyloxypropyltrimethoxysilane), methanol, formic acid, ultrapure water, p-tert-butylphenol, MAA (methacrylic acid), acetonitrile, EGDMA (ethylene glycol dimethacrylate), AIBN (azobisisobutyronitrile), acetic acid, phenol, m-cresol, 4-methyl-2-pentanone, ethyl acetate, BSTFA (containing 1% TMCS).

[0028] Experimental objective: A method for preparing a gas chromatographic standard for liquid test material is provided.

[0029] Experimental steps: S1: Take 100g of magnetic Fe3O4 nanoparticles, then add 50g of MOF-5 organic framework material to obtain Fe3O4@MOF-5 by solvothermal method, then add 50g of graphene oxide and ultrasonically disperse at a frequency of 60kHz for 30min to prepare magnetic metal-organic framework / graphene composite material Fe3O4@MOF-5@GO. S2: Disperse 20 mg Fe3O4@MOF-5@GO in 50 mL of water / organic diluent containing the target analyte, then add 1 g of anhydrous sodium sulfate and 0.5 g of sodium chloride and shake for 15 minutes. S3: Separate the magnetic adsorbent from the final mixture obtained in S2 using an external magnetic field, discard the supernatant, and then wash the adsorbent with 5 mL of 5% methanol aqueous solution and 5 mL of ultrapure water in sequence to remove weakly bound impurities and salts. Repeat the washing twice and then dry it under nitrogen flow at room temperature for 5 minutes. S4: Add 2 mL of a 1:1 mixture of acetonitrile and ethyl acetate to the dried adsorbent in S3 and elute with sonication for 5 minutes. Then, collect the eluent by magnetic separation. Elute the remaining adsorbent with 2 mL of acetonitrile solution containing 0.2% formic acid with sonication for 5 minutes and combine the two eluents. S5: The last eluent from S4 was dehydrated by passing it through an anhydrous sodium sulfate column, and then the dehydrated eluent was dried in a water bath at 40°C with pure nitrogen. S6: Add 50 μL of BSTFA containing 1% TMCS and 50 μL of acetonitrile to the residue. After sealing, place the mixture in a microwave reactor and irradiate it at 300 W power and 70°C for 3 minutes. After cooling to room temperature, add 10 μL of deuterated toluene-d8 containing 10 μg / mL and deuterated phenol-d6 to obtain the gas chromatographic analysis standard.

[0030] Experimental results:

[0031] Example 1 uses a magnetic metal-organic framework / graphene composite material Fe3O4@MOF-5@GO as an adsorbent. This material combines the high specific surface area and tunable pore size of MOF-5 with the π-π conjugation effect of graphene oxide. Through multiple effects such as hydrophobicity, π-π stacking, hydrogen bonding, and size sieving, it can simultaneously enrich a variety of polar and non-polar organic solvents, including alcohols, ketones, esters, halogenated hydrocarbons, and aromatic hydrocarbons. Combined with stepwise elution and BSTFA microwave-assisted derivatization, the chromatographic response and detection sensitivity of the target analytes are effectively improved. Simultaneous analysis of 32 common organic solvents is achieved with detection limits as low as 0.06–0.30 μg / L and enrichment factors of 82–98 times, significantly expanding the applicability of magnetic solid-phase extraction in liquid phase analytes.

[0032] Example

[0033] This embodiment provides a method for preparing 4-methyl-2-pentanone standard for GC, the specific implementation steps of which include: Experimental materials: Graphitized carbon black, carbon molecular sieve, [BMIM]PF6 ionic liquid, high-purity nitrogen, toluene-d8 (internal standard), methanol, benzene standard solution, toluene standard solution, ethylbenzene standard solution, o-xylene standard solution, and high-purity helium.

[0034] Experimental objective: A method for preparing gas chromatographic analytical standards for gaseous test substances is provided.

[0035] Experimental steps: S1: Graphitized carbon black and carbon molecular sieve are mixed evenly at a mass ratio of 2:1 to obtain an adsorbent. Then, 30 mg of adsorbent is taken and 5 wt% of [BMIM]PF6 ionic liquid is added to it and ultrasonically impregnated for 30 minutes. After the solvent has completely evaporated, the liquid is evenly coated on the surface of the adsorbent. S2: The modified adsorbent is filled into the middle of a stainless steel hollow needle. The filled needle extraction device is placed in an aging furnace at 250°C and aged for 4 hours with high-purity nitrogen gas introduced at a rate of 50 mL / min to obtain a composite adsorbent needle extraction device. S3: Inject 1 μL of a 100 ng / μL toluene-d8 methanol solution into the needle extraction apparatus and purge with nitrogen for 2 minutes; S4: Using a dynamic gas mixing system, benzene, toluene, ethylbenzene, and o-xylene standard solutions are injected into the vaporization chamber to prepare a BTEX mixed standard gas with a concentration of 10 ppb. The needle extraction device prepared in S2 is connected to the gas sampling pump, the BTEX mixed standard gas is introduced and the flow rate is controlled at 100 mL / min, and then the standard gas is drawn off at a flow rate of 50 mL / min. S5: Remove the enriched needle extraction device and immediately insert it into a gas chromatograph with an injection port temperature of 250℃. At the same time, start the programmed temperature rise thermal desorption, set the initial injection port temperature to 50℃, and rapidly heat it to 250℃ at a rate of 10℃ / s and hold it for 2 minutes. The desorbed target analytes are carried by high-purity helium carrier gas and directly enter the chromatographic column for separation.

[0036] Experimental results: See Table 2 for details.

[0037]

[0038] Table 2: Test Results of Example 2 Example 2 employs a method for preparing gas chromatographic analysis standards for gaseous test samples, addressing the problems of inconvenient portability, high storage pressure, and easily fluctuating concentrations associated with traditional gaseous standards in steel cylinders. This example utilizes needle extraction with a particle-liquid modified composite adsorbent, resulting in significantly improved enrichment efficiency for gaseous test samples, excellent moisture resistance, accurate internal standard calibration, convenient operation, and environmental friendliness.

[0039] Example 3 This embodiment provides a method for preparing 4-methyl-2-pentanone standard for GC, the specific implementation steps of which include: Experimental materials: Magnetic iron oxide nanoparticles, ZIF-8 precursor (2-methylimidazole, zinc nitrate hexahydrate), graphene oxide, aminated multi-walled carbon nanotubes, methanol, acetonitrile, anhydrous sodium sulfate, sodium chloride, triethylamine, acetylacetone, trifluoroacetylacetone, BSTFA containing 1% TMCS, pyridine, deuterated benzoic acid-d5, deuterated naphthalene-d8, magnesium chloride, sodium chloride, potassium chloride, sodium tetraborate, benzoic acid, tris(hydroxymethyl)aminomethane, magnesium sulfate, citric acid, and high-purity helium.

[0040] Experimental objective: A method for preparing gas chromatographic analysis standards for solid test substances is provided.

[0041] Experimental steps: S1: 100g of Fe3O4 nanoparticles and 50g of ZIF-8 metal-organic framework material were weighed and then Fe3O4@ZIF-8 was prepared by solvothermal method. Then, 50g of multi-walled carbon nanotubes and 50g of aminated graphene oxide were loaded sequentially by electrostatic self-assembly to prepare the multifunctional magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2. S2: Weigh 1.0 g of solid sample, grind it and place it in a 50 mL centrifuge tube. Then add 10 mL of methanol:water = 1:1 extraction solution and shake and stir for 5 minutes. Then extract it with ultrasound at 50 kHz frequency for 15 minutes. Finally, add 20 mg of the magnetic composite material prepared in S1 and continue to shake for 20 minutes. S3: Separate the magnetic adsorbent obtained in S2 using an external magnetic field, then discard the supernatant, and wash the adsorbent sequentially with 5 mL of ultrapure water, 5 mL of 5% methanol aqueous solution and 5 mL of n-hexane, and finally dry it with nitrogen at room temperature of 25°C for 5 minutes. S4: Add 2 mL of acetonitrile solution containing 0.5% triethylamine to the adsorbent, then elute with ultrasound at 50 kHz for 5 minutes, collect eluent A by magnetic separation, add 2 mL of acetonitrile solution containing 0.1 mol / L acetylacetone to the residual adsorbent, elute with ultrasound for 5 minutes, and collect eluent B. S5: Eluent A collected in S4 was dried in nitrogen at 40°C. Then, 50 μL of BSTFA containing 1% TMCS and 50 μL of acetonitrile were added sequentially. After sealing, the eluent was heated to 80°C and kept at that temperature for 30 minutes. Eluent B was dried in nitrogen at 40°C. Then, 50 μL of trifluoroacetylacetone, 50 μL of acetonitrile and 10 μL of pyridine were added as catalysts. After sealing, the eluent was heated to 60°C and kept at that temperature for 20 minutes to obtain the chelated derivative. S6: Combine eluent A and eluent B obtained from the chelated derivative in S5, then add 10 μL of an internal standard mixed solution containing 10 μg / mL deuterated benzoic acid-d5 and 10 μg / mL deuterated naphthalene-d8, and finally dilute to 200 μL with acetonitrile and pass through a 0.22 μm filter membrane to obtain the gas chromatographic analytical standard.

[0042] Experimental results: See Table 3 for details.

[0043] Table 3: Test Results of Example 3 Example 3 utilizes a multifunctional magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2. Through the coordination of ZIF-8, the hydrophobic adsorption of carbon nanotubes, and the electrostatic and hydrogen bonding interactions of aminated graphene oxide, simultaneous enrichment of various inorganic salts and organic compounds, such as magnesium chloride, sodium chloride, potassium chloride, sodium tetraborate, benzoic acid, tris(hydroxymethyl)aminomethane, magnesium sulfate, and citric acid, is achieved. A stepwise elution strategy is employed to collect inorganic ions and organic acid components separately, and each target analyte is derivatized by acetylacetone chelation and BSTFA silanization, respectively, converting them into volatile derivatives suitable for gas chromatography analysis.

[0044] Example 4 This embodiment provides a method for preparing 4-methyl-2-pentanone standard for GC, the specific implementation steps of which include: Experimental materials: Fe3O4@SiO2 particles, toluene, MPS (3-methacryloyloxypropyltrimethoxysilane), methanol, formic acid, ultrapure water, p-tert-butylphenol, MAA (methacrylic acid), acetonitrile, EGDMA (ethylene glycol dimethacrylate), AIBN (azobisisobutyronitrile), acetic acid, phenol, m-cresol, 4-methyl-2-pentanone, ethyl acetate, BSTFA (containing 1% TMCS).

[0045] Experimental objective: The preparation parameters of the ultra-drying agent and GC standard were adjusted to investigate the effect of the parameters on the performance.

[0046] Experimental steps: S1: Take 100g of magnetic Fe3O4 nanoparticles, then add 30g of MOF-5 organic framework material to obtain Fe3O4@MOF-5 by solvothermal method, then add 25g of graphene oxide and ultrasonically disperse at a frequency of 60kHz for 15min to prepare magnetic metal-organic framework / graphene composite material Fe3O4@MOF-5@GO. S2: Disperse 20 mg Fe3O4@MOF-5@GO in 50 mL of water / organic diluent containing the target analyte, then add 1 g of anhydrous sodium sulfate and 0.5 g of sodium chloride and shake for 15 minutes. S3: Separate the magnetic adsorbent from the final mixture obtained in S2 using an external magnetic field, discard the supernatant, and then wash the adsorbent with 5 mL of 5% methanol aqueous solution and 5 mL of ultrapure water in sequence to remove weakly bound impurities and salts. Repeat the washing twice and then dry it under nitrogen flow at room temperature for 5 minutes. S4: Add 2 mL of a 1:1 mixture of acetonitrile and ethyl acetate to the dried adsorbent in S3 and elute with sonication for 5 minutes. Then, collect the eluent by magnetic separation. Elute the remaining adsorbent with 2 mL of acetonitrile solution containing 0.2% formic acid with sonication for 5 minutes and combine the two eluents. S5: The last eluent from S4 was dehydrated by passing it through an anhydrous sodium sulfate column, and then the dehydrated eluent was dried in a water bath at 40°C with pure nitrogen. S6: Add 50 μL of BSTFA containing 1% TMCS and 50 μL of acetonitrile to the residue. After sealing, place the mixture in a microwave reactor and irradiate it at 200 W power and 60°C for 2 minutes. After cooling to room temperature, add 10 μL of deuterated toluene-d8 containing 10 μg / mL and deuterated phenol-d6 to obtain the gas chromatographic analysis standard.

[0047] Experimental results: See Table 4 for details.

[0048] Table 4: Test Results of Example 4

[0049] Example 4 reduced the amounts of MOF-5 and graphene oxide and shortened the ultrasonic dispersion time compared to Example 1. This resulted in a decrease in the density of active adsorption sites and a smaller specific surface area in the composite material, weakening the multiple synergistic adsorption effects such as hydrophobicity, π-π stacking, and hydrogen bonding. Consequently, the extraction recovery rate and enrichment factor of the target analyte decreased. Simultaneously, the power, temperature, and time of microwave-assisted derivatization were all lower than in Example 1, leading to incomplete BSTFA silanization and a decreased derivatization yield of the target analyte. This resulted in a lower chromatographic response, a higher detection limit, and poorer precision. The reduction in material composition and reaction conditions is the fundamental reason why the overall performance of Example 4 is inferior to that of Example 1.

[0050] Example 5 This embodiment provides a method for preparing 4-methyl-2-pentanone standard for GC, the specific implementation steps of which include: Magnetic iron oxide nanoparticles, ZIF-8 precursor (2-methylimidazole, zinc nitrate hexahydrate), graphene oxide, aminated multi-walled carbon nanotubes, methanol, acetonitrile, anhydrous sodium sulfate, sodium chloride, triethylamine, acetylacetone, trifluoroacetylacetone, BSTFA containing 1% TMCS, pyridine, deuterated benzoic acid-d5, deuterated naphthalene-d8, magnesium chloride, sodium chloride, potassium chloride, sodium tetraborate, benzoic acid, tris(hydroxymethyl)aminomethane, magnesium sulfate, citric acid, and high-purity helium.

[0051] Experimental objective: The preparation parameters of solid test samples for gas chromatography analysis were adjusted to investigate the effect of parameter changes on the gas chromatography analysis standards.

[0052] Experimental steps: S1: 100g of Fe3O4 nanoparticles and 30g of ZIF-8 metal-organic framework material were weighed and then Fe3O4@ZIF-8 was prepared by solvothermal method. Then, 25g of multi-walled carbon nanotubes and 25g of aminated graphene oxide were loaded sequentially by electrostatic self-assembly to prepare the multifunctional magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2. S2: Weigh 1.0 g of solid sample, grind it and place it in a 50 mL centrifuge tube. Then add 10 mL of methanol:water = 1:1 extraction solution and shake and stir for 5 minutes. Then extract with ultrasound at 50 kHz frequency for 15 minutes. Finally, add 20 mg of the magnetic composite material prepared in S1 and continue shaking for 10 minutes. S3: Use an external magnetic field to separate the magnetic adsorbent obtained in S2, then discard the supernatant, and then use 5 mL of ultrapure water and 5 mL of 5% methanol aqueous solution in sequence, and finally blow dry with nitrogen at room temperature of 25°C for 5 minutes. S4: Add 2 mL of acetonitrile solution containing 0.5% triethylamine to the adsorbent, then elute with ultrasound at 50 kHz for 3 minutes, collect eluent A by magnetic separation, add 2 mL of acetonitrile solution containing 0.05 mol / L acetylacetone to the residual adsorbent, elute with ultrasound for 3 minutes, and collect eluent B. S5: Eluent A collected in S4 was dried in nitrogen at 40°C. Then, 50 μL of BSTFA containing 1% TMCS and 50 μL of acetonitrile were added sequentially. After sealing, the eluent was heated to 70°C and kept at that temperature for 15 minutes. Eluent B was dried in nitrogen at 40°C. Then, 50 μL of trifluoroacetylacetone, 50 μL of acetonitrile and 10 μL of pyridine were added as catalysts. After sealing, the eluent was heated to 50°C and kept at that temperature for 20 minutes to obtain the chelated derivative. S6: Combine eluent A and eluent B obtained from the chelated derivative in S5, then add 10 μL of an internal standard mixed solution containing 10 μg / mL deuterated benzoic acid-d5 and 10 μg / mL deuterated naphthalene-d8, and finally dilute to 200 μL with acetonitrile and pass through a 0.22 μm filter membrane to obtain the gas chromatographic analytical standard.

[0053] Experimental results: See Table 5 for details.

[0054] Table 5: Test Results of Example 5

[0055] Example 5, based on Example 3, reduced the amounts of ZIF-8, multi-walled carbon nanotubes, and aminated graphene oxide, and shortened the adsorption oscillation and ultrasonic elution times. This significantly weakened the multiple adsorption interactions of the composite material, including metal coordination, π-π stacking, electrostatics, and hydrogen bonding, resulting in a decreased enrichment capacity for inorganic salts and organic acids. Simultaneously, the reduced eluent concentration and insufficient derivatization temperature and time led to incomplete chelation and silanization reactions, incomplete desorption of the target analyte, and low derivative yields. Ultimately, this resulted in performance indicators such as recovery rate, precision, and detection limit being inferior to those of Example 3. The reduction in the functional components of the material and the weakening of the reaction conditions were the key factors contributing to the performance decline in Example 5.

[0056] Comparative Example 1 This embodiment provides a method for preparing conventional gas chromatography analytical standards, the specific implementation steps of which include: Experimental materials: Methanol, acetonitrile, ethyl acetate, n-hexane, anhydrous sodium sulfate, sodium chloride, ultrapure water, benzene standard solution, toluene standard solution, ethylbenzene standard solution, o-xylene standard solution, phenol, m-cresol, p-tert-butylphenol, C1-C3 mixed alcohol standards, C6-C10 mixed alkane standards, nitrogen, and helium.

[0057] Experimental objective: A traditional method for preparing gas chromatographic analytical standards is provided as a comparative benchmark for the method of this invention.

[0058] Experimental steps: S1: Preparation of liquid test standard: Take 10 mL of mixed standard solution containing the target analyte, add 5 g of anhydrous sodium sulfate to dehydrate, shake for 5 minutes and let stand for 10 minutes, take the supernatant and filter it through a 0.45 μm organic phase filter membrane to obtain the crude extract of liquid test analyte; S2: Preparation of gaseous test standard: Using the static gas mixing method of steel cylinder, benzene, toluene, ethylbenzene and o-xylene standard solutions are injected into a pre-vacuumed stainless steel gas cylinder in proportion, and high-purity nitrogen is filled to the set pressure to prepare a BTEX mixed standard gas with a concentration of 10 ppb. S3: Preparation of solid test standard: Weigh 1.0 g of solid sample, place it in a 50 mL centrifuge tube, add 10 mL of methanol-water mixed solvent, vortex for 5 minutes, let stand for 30 minutes to extract, take the supernatant and filter it through a 0.45 μm filter membrane to obtain solid test extract; S4: Transfer the samples prepared in S1, S2, and S3 into injection vials and perform gas chromatography analysis directly.

[0059] Experimental results: Comparative Example 1 employed a traditional gas chromatography (GC) analytical standard preparation method. Its main technical drawbacks are: liquid test samples only undergo simple dehydration and filtration, lacking an effective enrichment step, resulting in high detection limits for trace components and an enrichment factor of only 1, which fails to meet trace analysis requirements. Gaseous test samples utilize a static gas mixing method using gas cylinders, which suffers from inconvenience in carrying cylinders, high storage pressure, volatile concentrations, and difficulty in controlling mixing accuracy. Furthermore, the lack of internal standard correction leads to poor quantitative accuracy. Solid test samples employ only simple solvent extraction, lacking targeted enrichment and derivatization treatments. Inorganic salt compounds are difficult to extract effectively and analyze by GC, resulting in low recovery rates, high detection limits, and an inability to simultaneously analyze multiple types of target compounds. The entire preparation process lacks any internal standard, failing to correct for systematic errors and matrix effects during sample pretreatment and instrument analysis, resulting in poor quantitative precision and accuracy.

[0060] Comparing the examples and comparative examples, Example 1, through multiple adsorption of Fe3O4@MOF-5@GO and microwave-assisted derivatization, achieved the highest efficiency in enriching liquid organic matter, demonstrating the best performance. Example 2 employed ionic liquid-modified needle extraction, achieving a gaseous BTEX enrichment efficiency of 94.9%–97.8%, but with limited adsorption capacity. Example 3 utilized multi-level core-shell composite materials and stepwise derivatization to simultaneously analyze solid inorganic salts and organic acids, but the preparation was complex. Examples 4 and 5 showed a significant performance decline due to reduced material usage or weakened conditions. The traditional method in Comparative Example 1 lacked enrichment, derivatization, and internal standards, resulting in high detection limits and low recoveries. This invention designs specific materials and processes for different states of matter, significantly improving analytical performance and applicability, demonstrating outstanding technological advancement.

[0061] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims.

[0062] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing GC standard using 4-methyl-2-pentanone, characterized in that, Specifically, this includes methods for preparing gas chromatographic analysis standards for solid test substances, methods for preparing gas chromatographic analysis standards for liquid test substances, and methods for preparing gas chromatographic analysis standards for gas test substances.

2. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 1, characterized in that, The specific method for preparing the gas chromatographic analysis standard of the liquid test material includes: A1: Take 80-100 parts by weight of magnetic Fe3O4 nanoparticles, then add 25-50 parts by weight of MOF-5 organic framework material to obtain Fe3O4@MOF-5 by solvothermal method, then add 25-50 parts by weight of graphene oxide GO and ultrasonically disperse at a frequency of 60kHz for 15-30min to prepare magnetic metal-organic framework / graphene composite material Fe3O4@MOF-5@GO; A2: Take 10-20 parts by weight of Fe3O4@MOF-5@GO and disperse it in 25-50 parts by weight of water / organic diluent containing the target analyte. Then add 1-2 parts by weight of anhydrous sodium sulfate and 0.5-1 parts by weight of sodium chloride and shake for 15 minutes. A3: Separate the magnetic adsorbent from the final mixture obtained in A2 using an external magnetic field, discard the supernatant, and then wash the adsorbent with 5-8 parts by weight of 5% methanol aqueous solution and 5-8 parts by weight of ultrapure water in sequence to remove weakly bound impurities and salts. Repeat the washing twice and then dry under nitrogen flow at room temperature for 5 minutes. A4: Add 2-3 parts by weight of a mixed solvent of acetonitrile:ethyl acetate = 1:1 to the dried adsorbent in A3 and sonicate for 5 minutes. Then collect the eluent by magnetic separation. Elute the residual adsorbent with 2-3 parts by weight of acetonitrile solution containing 0.2% formic acid for 5 minutes by sonication. Combine the two eluents. A5: The last eluent from A4 was dehydrated by passing it through an anhydrous sodium sulfate column, and then the dehydrated eluent was dried in a water bath at 40°C with pure nitrogen. A6: Add 0.05-0.1 parts by weight of BSTFA containing 1% TMCS and 0.05-0.1 parts by weight of acetonitrile to the residue. After sealing, place the mixture in a microwave reactor and irradiate it at 300 W power and 70°C for 3 minutes. After cooling to room temperature, add 0.10-0.2 parts by weight of deuterated toluene-d8 containing 10 μg / mL and deuterated phenol-d6 containing 10 μg / mL to obtain the gas chromatographic analysis standard.

3. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 2, characterized in that, The MOF-5 organic framework material in A1 has a microporous crystal structure, formed by the coordination self-assembly of terephthalic acid and zinc ions, and has a three-dimensional cubic network topology with a pore size of 0.8~1.2 nm.

4. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 2, characterized in that... In A1, Fe3O4@MOF-5@GO has a core-shell structure with magnetic Fe3O4 nanoparticles as the core, a MOF-5 layer in the middle, and graphene oxide (GO) as the outer layer.

5. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 1, characterized in that, The specific method for preparing the gaseous test sample gas chromatographic analysis standard includes: B1: Graphitized carbon black and carbon molecular sieve are mixed evenly at a mass ratio of 2:1 to obtain an adsorbent. Then, 30-40 parts by weight of the adsorbent are taken and 5 wt% of [BMIM]PF6 ionic liquid is added to it and ultrasonically impregnated for 30 minutes. After the solvent has completely evaporated, the liquid is evenly coated on the surface of the adsorbent. B2: The modified adsorbent is filled into the middle of a stainless steel hollow needle. The filled needle extraction device is placed in an aging furnace at 250°C and aged for 4 hours with high-purity nitrogen gas introduced at a rate of 50 mL / min to obtain a composite adsorbent needle extraction device. B3: Inject 0.1~0.2 parts by weight of a methanol solution of toluene-d8 with a concentration of 100 ng / μL into the needle extraction device and purge with nitrogen for 2 minutes; B4: Using a dynamic gas mixing system, benzene, toluene, ethylbenzene, and o-xylene standard solutions are injected into the vaporization chamber to prepare a BTEX mixed standard gas with a concentration of 10 ppb. The needle extraction device prepared in B2 is connected to the gas sampling pump, the BTEX mixed standard gas is introduced and the flow rate is controlled at 100 mL / min, and then the standard gas is drawn off at a flow rate of 50 mL / min. B5: Remove the enriched needle extraction device and immediately insert it into a gas chromatograph with an injection port temperature of 250℃. At the same time, start the programmed temperature rise thermal desorption, set the initial injection port temperature to 50℃, and rapidly heat it to 250℃ at a rate of 10℃ / s and hold it for 2 minutes. The desorbed target analytes are carried by high-purity helium carrier gas and directly enter the chromatographic column for separation.

6. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 5, characterized in that, The graphitized carbon black described in B1 is a layered or flocculent aggregate of graphite microcrystals, formed by high-temperature graphitization of carbon black, with a spacing of 0.335~0.340 nm between the graphite microcrystals.

7. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 5, characterized in that, The carbon molecular sieve described in B1 is a microporous carbonaceous adsorbent material with a regular slit-like or columnar pore structure and a pore size distribution concentrated in the range of 0.4~0.7 nm.

8. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 1, characterized in that, The specific method for preparing the gas chromatographic analysis standard of the solid test material includes: C1: Weigh 80-100 parts by weight of Fe3O4 nanoparticles and 25-50 parts by weight of ZIF-8 metal-organic framework material, and then prepare Fe3O4@ZIF-8 by solvothermal method. Then, load 25-50 parts by weight of multi-walled carbon nanotubes and 25-50 parts by weight of aminated graphene oxide through electrostatic self-assembly to prepare multifunctional magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2. C2: Weigh 1-2 parts by weight of solid sample, grind it and place it in a centrifuge tube. Then add 8-10 parts by weight of methanol:water = 1:1 extraction solution and shake and stir for 5 minutes. Then extract with ultrasound at 50 kHz frequency for 15 minutes. Finally add 10-20 parts by weight of the magnetic composite material prepared in C1 and continue to shake for 20 minutes. C3: The magnetic adsorbent obtained in C2 is separated by an external magnetic field. The supernatant is then discarded. The adsorbent is then washed with 5-8 parts by weight of ultrapure water, 5-8 parts by weight of 5% methanol aqueous solution, and 5-8 parts by weight of n-hexane in sequence. Finally, it is dried with nitrogen at room temperature of 25°C for 5 minutes. C4: Add 2-5 parts by weight of acetonitrile solution containing 0.5% triethylamine to the adsorbent, then elute with ultrasound at 50 kHz for 5 minutes, collect eluent A by magnetic separation, and add 2-5 parts by weight of acetonitrile solution containing 0.1 mol / L acetylacetone to the residual adsorbent, elute with ultrasound for 5 minutes, and collect eluent B. C5: Eluent A collected in C4 was dried in nitrogen at 40°C. Then, 0.05-0.1 parts by weight of BSTFA containing 1% TMCS and 0.05-0.1 parts by weight of acetonitrile were added sequentially. After sealing, the eluent was heated to 80°C and kept at that temperature for 30 minutes. Eluent B was dried in nitrogen at ambient temperature of 40°C. Then, 0.05-0.1 parts by weight of trifluoroacetylacetone, 0.05-0.1 parts by weight of acetonitrile and 0.10-0.20 parts by weight of pyridine were added as catalysts. After sealing, the eluent was heated to 60°C and kept at that temperature for 20 minutes to obtain the chelated derivative. C6: Combine eluent A and eluent B obtained from the chelated derivative in C5, then add 0.10~0.20 parts by weight of an internal standard mixed solution containing 10 μg / mL deuterated benzoic acid-d5 and 10 μg / mL deuterated naphthalene-d8, and finally pass it through a 0.22 μm filter membrane to obtain a gas chromatographic analytical standard.

9. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 8, characterized in that, The multi-walled carbon nanotubes described in C1 have a hollow tubular structure with a diameter of 10-30 nm and a length of 5-15 μm. The aminated graphene oxide described in C1 has a sheet structure with a sheet thickness of 1-3 nm and amino functional groups grafted onto its surface.

10. The method for preparing 4-methyl-2-pentanone standard for GC as described in claim 8, characterized in that, The magnetic composite material Fe3O4@ZIF-8@MWCNTs@GO-NH2 in C1 has a multi-level core-shell structure. Fe3O4 magnetic nanoparticles serve as the core, ZIF-8 forms the middle layer, multi-walled carbon nanotubes form a three-dimensional conductive network running through it, and aminated graphene oxide serves as the outer coating layer, forming a composite microsphere structure that combines magnetism, porous adsorption, and surface functionalization.

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