Method for analyzing methylsiloxane based on GC-APCI-MS / MS

Abstract

The invention discloses a method for analyzing methylsiloxane based on GC-APCI-MS / MS, and relates to the technical field of analysis and detection. According to the method, a gas chromatography-mass spectrometry technology is adopted, an atmospheric pressure chemical ionization source is taken as an ion source, ultrapure water is introduced as an ionization auxiliary agent, and gas chromatography conditions (including sample inlet parameters, chromatographic column configuration and a heating program) and mass spectrometry conditions (adopting a multi-reaction monitoring mode) are optimized, so that the analysis of the annular and linear methylsiloxane is realized. The method has the advantages of low background pollution, high sensitivity and precision, and is suitable for qualitative and quantitative analysis of methylsiloxane in various environmental media.

Description

Technical Field

[0001] This invention relates to the field of analytical detection technology, and in particular to a method for analyzing methylsiloxanes based on GC-APCI-MS / MS. Background Technology

[0002] Methylsiloxanes are a class of synthetically produced organic compounds with no natural origin. Their main chain has a Si-O structure, with methyl side chains attached to silicon atoms. Based on their chemical structure, methylsiloxanes can be classified into cyclic (cyclomethylsiloxanes) and linear compounds (also known as polydimethylsiloxanes). These compounds exhibit high volatility and lipophilicity. In industry, they are mainly used as synthetic intermediates for high molecular weight organosilicon polymers and are also widely used in cosmetics, toiletries, and other daily chemical products. Due to their unique and excellent physicochemical properties, the production and use of methylsiloxanes have continued to increase in recent years, leading to significant releases into the environment. Currently, methylsiloxanes have been detected in various environmental media, such as ng-μg / L in water, ng / g in sediments, soil, dust, and biota, and typically hundreds to thousands of ng / m³ in air samples.

[0003] Despite ongoing debate regarding the potential risks of methylsiloxanes, studies have shown that their semi-volatile nature and atmospheric persistence may lead to long-distance migration; their lipophilicity and low biodegradability give them the potential for bioaccumulation and amplification. Some methylsiloxanes are even suspected of having harmful effects on organisms. Therefore, methylsiloxanes have been identified as "emerging pollutants." To clarify the environmental risks of these chemicals, obtaining data on their concentration levels and fate behavior in the environment is crucial. Therefore, there is an urgent need to develop rapid, sensitive, and robust multi-media analytical methods for methylsiloxanes.

[0004] Because methylsiloxanes are widely used in everyday consumer goods and industrial products, they can be contaminated from various sources, including analytical equipment components and laboratory consumables, ultimately severely impairing test results. This significantly increases the difficulty of methylsiloxane analysis, leading to a lack of routinely used analytical methods. This is also one of the reasons why methylsiloxanes have not been included in environmental monitoring programs. Therefore, it is essential to develop operating procedures and background control strategies that minimize the possibility of external cross-contamination. Currently, there is no standard method for the analysis of methylsiloxanes. Due to their volatility, almost all studies primarily use gas chromatography-mass spectrometry (GC-EI-MS) based on electron ionization (EI) sources as the quantitative technique. Therefore, it is necessary to provide a low-background, high-sensitivity, and high-precision quantitative method for the analysis of cyclic and linear methylsiloxanes using atmospheric pressure chemical ionization source-based gas chromatography-mass spectrometry (GC-APCI-MS / MS). Summary of the Invention

[0005] The purpose of this invention is to provide a method for analyzing methylsiloxanes based on GC-APCI-MS / MS, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a method for analyzing methylsiloxanes based on GC-APCI-MS / MS, comprising the following steps:

[0008] Methylsiloxane was analyzed by gas chromatography-mass spectrometry using an atmospheric pressure chemical ionization source (APCI). Ultrapure water was introduced into the ion source as an ionization aid in an open manner, with a volume of 1000 μL.

[0009] The gas chromatography conditions include:

[0010] The injection port is a splitless injection port with an injection port temperature of 300℃ and a purge flow rate of 3.0 mL / min. The septum is a valve micro-seal septum, the inner liner is an ultra-inert splitless inner liner with a glass frit core at the bottom, and the O-ring of the inner liner is made of graphite.

[0011] The chromatographic column used was a DB-WAX column, 15m × 0.25mm × 0.25μm, with high-purity helium as the carrier gas, in constant flow mode at a flow rate of 1.0 mL / min;

[0012] Temperature program: Initial temperature 40℃, hold for 2 min, increase to 255℃ at 15℃ / min, hold for 8.67 min, total time 25 min;

[0013] Mass spectrometry conditions include:

[0014] The transfer line temperature was 320℃, the ion source temperature was 150℃, and the auxiliary gas, cone gas, and makeup gas were all nitrogen, with flow rates of 200 L / Hr, 50 L / Hr, and 300 mL / min, respectively. APCI positive mode was used, with a corona needle current of 0.5 μA and a cone voltage of 30V. The mass spectrometry acquisition mode was multiple reaction monitoring (MRM).

[0015] As a further preferred embodiment of the present invention, the evaporation rate of the ionization aid is 0.334±0.004 μL / min, and the evaporation process decreases linearly.

[0016] As a further preferred embodiment of the present invention, the method is used to detect cyclic methylsiloxanes and linear methylsiloxanes.

[0017] Cyclic methylsiloxanes include octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxane (D7), hexadecamethylcyclooctasiloxane (D8), or octadecylmethylcyclononasiloxane (D9).

[0018] The linear methylsiloxanes include: decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5), tetradecamethylhexasiloxane (L6), hexadecylmethylheptasiloxane (L7), octadecylmethyloctasiloxane (L8), eicosamethylnonasiloxane (L9), docosamethyldecasiloxane (L10), tetracosamethylundecasiloxane (L11), and hexadecyldecasiloxane. Hexacosamethyldodecasiloxane (L12), Octacosamethyltridecasiloxane (L13), Triacontamethyltetradecasiloxane (L14), Dotriacontamethylpentadecasiloxane (L15), Tetraiacontamethylhexadecasiloxane (L16), Hexatriacontamethylheptadecasiloxane (L17), or Octatriacontamethyloctadecasiloxane (L18).

[0019] As a further preferred embodiment of the present invention, the sample pretreatment step includes:

[0020] For atmospheric samples: Polyurethane foam collected from the samples was ultrasonically extracted with n-hexane, concentrated, and then filtered.

[0021] For particulate matter samples: the collected quartz filter membrane was cut into pieces and extracted with hexane by ultrasonication, then concentrated and filtered.

[0022] A two-piece (pistonless) syringe and a polytetrafluoroethylene (PTFE) needle filter are used for filtration.

[0023] As a further preferred embodiment of the present invention, 30 cm and 70 cm untreated, deactivated fused silica tubes (0.25 mm id) are used as the front guard column and the rear guard column, respectively, and ultra-inert metal two-way valves are used to connect them to the chromatographic column.

[0024] The septum of the chromatographic vial cap used in the sample pretreatment is made of polytetrafluoroethylene / tert-butyl rubber.

[0025] As a further preferred embodiment of the present invention, the precursor ion of the target analyte in the method is [M+H]⁺, and the daughter ions are quantitative ions and qualitative ions.

[0026] The method of this invention is applicable to the qualitative and quantitative analysis of methylsiloxanes in environmental media, including atmospheric, particulate matter, water, sediment, soil and biota samples.

[0027] The present invention also provides a system for implementing the above method, comprising:

[0028] Gas chromatograph, equipped with DB-WAX column 15m×0.25mm×0.25μm;

[0029] The mass spectrometer is equipped with an atmospheric pressure chemical ionization source (APCI) and a multiple reaction monitoring mode (MRM).

[0030] An ionization aid introduction device is used to easily and stably introduce ultrapure water into an ion source.

[0031] As a further preferred embodiment of the present invention, the ionization aid introduction device is an open-top chromatographic bottle with a volume of 1000 μL.

[0032] The present invention discloses the following technical effects:

[0033] This invention provides a method for analyzing methylsiloxanes based on GC-APCI-MS / MS. By optimizing gas chromatography and mass spectrometry conditions, using an atmospheric pressure chemical ionization source (APCI), and introducing ultrapure water as an ionization aid, the method effectively promotes the generation of the target analyte precursor ion [M+H]⁺, significantly enhances the detection response, and improves the sensitivity and specificity of the method.

[0034] Meanwhile, by setting specific protective columns at the front and rear ends of the chromatographic column and using ultra-inert connecting components, this invention minimizes external cross-contamination during the analysis process, reduces background interference, and ensures the accuracy and reliability of the detection results.

[0035] This invention enables the effective separation of various cyclic and linear methylsiloxanes with good peak shapes, meeting the needs of qualitative and quantitative analysis. It is applicable to the detection of various environmental media samples such as air and particulate matter, providing a stable and efficient analytical method for environmental monitoring of methylsiloxanes, an emerging pollutant. This helps to more accurately grasp its content level in the environment and provides strong technical support for assessing its environmental risks. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is an overlay of the total ion chromatograms (TICs) of 21 methylsiloxane monomers under the optimal conditions of Example 1.

[0038] Figure 2 The graph shows the relative intensities of 21 target standard molecular ions and neutral lost ions in APCI / -H2O and APCI / +H2O, which is a comparative example 1.

[0039] Figure 3 For comparison of the full scan mass spectra of methylsiloxanes D4, D9, L4, and L15 in APCI / -H2O and APCI / +H2O in Comparative Example 1.

[0040] Figure 4 As a comparative example 1, the effect of the introduction method of the ionization aid (water) in the APCI ion source on the response of methylsiloxane.

[0041] Figure 5 The scatter plot shows the average evaporation rate of different initial ionization agent volumes in the APCI ion source for Comparative Example 1.

[0042] Figure 6 This is a comparative example 1, showing the relationship between the remaining volume of the ionization aid (water) in the APCI ion source and the storage time.

[0043] Figure 7 For the background comparison of different types of syringes and needle filters in Comparative Example 2: (a) Background comparison of cyclic siloxanes introduced by different types of syringes (below the limit of quantitation or undetected, plotted as 0); (b) Background comparison of linear siloxanes introduced by different types of syringes (below the limit of quantitation or undetected, plotted as 0); (c) Background comparison of cyclic siloxanes introduced by different types of needle filters (below the limit of quantitation or undetected, plotted as 0); (d) Background comparison of linear siloxanes introduced by different types of needle filters (below the limit of quantitation or undetected, plotted as 0).

[0044] Figure 8 For Comparative Example 2, the background of different types of chromatographic bottle cap septa, gas chromatographic injection port septa, and capillary columns was compared as follows: (a) Background comparison of cyclic siloxanes introduced by chromatographic bottle cap septa of different materials (below the limit of quantitation or undetected, plotted as 0); (b) Background comparison of linear siloxanes introduced by chromatographic bottle cap septa of different materials (below the limit of quantitation or undetected, plotted as 0); (c) Background comparison of cyclic siloxanes introduced by different types of gas chromatographic injection port septa (below the limit of quantitation or undetected, plotted as 0); (d) Background comparison of linear siloxanes introduced by different types of gas chromatographic injection port septa (below the limit of quantitation or undetected, plotted as 0); (e) Background comparison of methylsiloxanes introduced by different capillary columns (below the limit of quantitation or undetected, plotted as 0).

[0045] Figure 9 This is a comparison chart of the instrument quantitation limits of the GC-EI-MS method and the GC-APCI-MS / MS method, shown in Comparative Example 3. Detailed Implementation

[0046] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0047] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0048] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0049] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0050] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0051] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0052] Example 1

[0053] Establish and optimize gas chromatography conditions and mass spectrometry methods:

[0054] Methylsiloxane was analyzed using gas chromatography-mass spectrometry (GC-MS) with an atmospheric pressure chemical ionization source as the ion source.

[0055] Based on the degree of separation between each analyte and the background level, the gas chromatography conditions were optimized and determined as follows: (1) Injection port parameters: splitless injection, injection port temperature of 300℃; purge flow rate of 3.0 mL / min; valve micro-sealing septum; ultra-inert splitless liner (with glass frit at the bottom); O-ring of the liner is made of graphite. (2) Column parameters: DB-WAX column (15m×0.25mm×0.25μm) was used, high-purity helium was used as carrier gas, constant flow mode, flow rate of 1.0 mL / min; 30 cm and 70 cm untreated, deactivated fused silica tubes (0.25mm id) were used as the front guard column and the rear guard column (transfer line) respectively, and ultra-inert metal two-way valves were used to connect them to the column. (3) Heating program: Initial temperature 40℃, hold for 2 min, increase to 255℃ at 15℃ / min, hold for 8.67 min, total time is 25 min.

[0056] Based on the response value, signal-to-noise ratio, and peak area of ​​the analyte precursor ions, the optimized and determined mass spectrometry conditions were as follows: (1) The transfer line temperature was 320℃; the ion source temperature was 150℃; the auxiliary gas, cone gas, and supplementary gas (sheath gas) were all nitrogen, with flow rates of 200 L / Hr, 50 L / Hr, and 300 mL / min, respectively. (2) Ultrapure water was used as the ionization aid, and the current mode was adopted, using APCI positive mode, with a corona needle current of 0.5 μA and a cone voltage of 30V. (3) The mass spectrometry acquisition mode was multiple reaction monitoring (MRM). The chromatographic and mass spectrometric information of the target analytes detected by GC-APCI-MS / MS are shown in Tables 1-3.

[0057] Table 1

[0058]

[0059] Table 2

[0060]

[0061] Table 3

[0062]

[0063] RT: Retention time (min); RW: Scan window (min); Precursor ion: Prnt (m / z) (Siloxane precursor ions are all quasi-molecular ions, M+H) + Product ion: Product ion, * indicates quantitative ion; Cone voltage (V): cone; Collision energy (eV): Coll; Ion ratio (q / Q): Qualitative ion (q) / Quantitative ion (Q).

[0064] Pretreatment of the test sample:

[0065] (1) Atmospheric sample pretreatment: After collecting the sample, the polyurethane foam was placed in a 50mL centrifuge tube, and then 1 g of anhydrous sodium sulfate was added to remove water, followed by 30 mL of n-hexane and 50 ng of sodium sulfate. 13 C-D4 and 13 C6-D6 was extracted using ultrasonic extraction for 15 min, followed by centrifugation at low temperature for 5 min (4ºC, 3500 rpm). Extraction with n-hexane was repeated three times. The three extracts were combined (90 mL) and concentrated to approximately 0.5 mL using a rotary evaporator (20ºC, 100 rpm). The concentrated sample and washing buffer (n-hexane used to wash the inner wall of the rotary evaporator) were then transferred to a chromatographic vial, and 50 ng of [a specific extract / concentration solution] was added. 13 C-D5, then bring the volume to 1 mL with n-hexane, and then filter using a needle filter (PTFE).

[0066] (2) Pretreatment of particulate matter samples: The collected atmospheric particulate matter (PM2.5) samples were pretreated. 2.5 PM 10 TSP (Total Suspended Particulates), with PM2.5 2.5 (Dust as an example). PM2.5 will be collected. 2.5 The quartz filter membrane was shredded using ceramic scissors (washed with n-hexane before and after use) and placed in a 50 mL centrifuge tube. Then, 1 g of anhydrous sodium sulfate was added to remove water, followed by 5 mL of n-hexane and 50 ng of sodium sulfate. 13 C-D4 and 13 C6-D6 was extracted using ultrasonic extraction for 15 min, followed by centrifugation at low temperature for 5 min (4ºC, 3500 rpm). Extraction with n-hexane was repeated three times. The three extracts were combined (15 mL) and concentrated using a rotary evaporator (20ºC, 100 rpm) to approximately 0.5 mL. The concentrated sample and washing buffer (n-hexane used to wash the inner wall of the rotary evaporator) were then transferred to a chromatographic vial, and 50 ng of [a specific extract / concentration solution] was added. 13 C-D5, then bring the volume to 1 mL with n-hexane, and then filter using a needle filter (PTFE).

[0067] After the sample pretreatment was completed, the internal standard method of GC-APCI-MS / MS was used for detection by gas chromatography and mass spectrometry established above, and the sample was qualitatively and quantitatively analyzed by combining the standard curve equation.

[0068] The overlay plot of the total ion chromatogram (TIC) of 21 methyl groups under optimal conditions is shown below. Figure 1 ,Depend on Figure 1 It can be seen that the method of the present invention can completely separate 21 target substances in the target substance, with good peak shape and high response.

[0069] Table 4 shows the instrumental method detection limit (LOD), quantitation limit (LOQ), linear equation of the standard curve and its correlation coefficient, and the method detection limit for atmospheric and particulate matter samples under optimal conditions. The LOD range for 21 methylsiloxanes using the method of this invention is 0.03-0.88 ug / L, and the LOQ range is 0.06-0.99 ug / L. The repeatability of the LOQ lower limit for six consecutive injections is within 15.6% (0.17%-15.6%). The signal-to-noise ratio (S / N) of the LOD is ≥3, and the S / N of the LOQ is ≥10. The method detection limit (MDL) for atmospheric sample pretreatment ranges from 0.05-12.9 ng / L, and the method detection limit (MDL) for particulate matter sample pretreatment ranges from 2.21-75.1 ng / L.

[0070] Table 4. Linear range of target compound, linear equation of standard curve and its correlation coefficient, limit of detection of instrument, limit of quantitation of instrument, method recovery and limit of detection of method.

[0071]

[0072] Comparative Example 1

[0073] This comparative study optimizes and compares the effects of different ionization environments and the introduction of ionization aids on precursor ions in the MRM mass spectrometry method for methylsiloxanes, and optimizes the method and amount of ionization aids introduced. Methylsiloxanes were analyzed using gas chromatography-mass spectrometry (GC-MS) with an atmospheric pressure chemical ionization source and full scan mass spectrometry. In full scan mode, high concentrations of target methylsiloxane standards were injected (100 μg / L for D4-D9 and L4; 800 μg / L for PDMS (L5-L18)). Under conventional APCI conditions (without water introduction, referred to as APCI / −H2O or dry ion source) in positive mode, although the quasi-molecular ion [M+H] was recorded in the APCI / −H2O mass spectra of all target methylsiloxanes... + However, the APCI / −H2O mass spectra of the target methylsiloxane mainly show [M+H-CH4] as the main component. + Fragment ions form the base peak (except for L11, L13, L16, L17, and L18, with relative ionic intensities of 27%, 12.8%, 33.8%, 0.46%, and 25.8%, respectively), while [M+H]... + The relative strength of the ions ranges from 0.22% to 27.6% (see...). Figure 2 ).

[0074] A chromatographic vial filled with ultrapure water is placed inside the ion source. Water, used as an ionization aid, is injected into the APCI source (referred to as APCI / +H₂O or a wet ion source). Injection of water effectively inhibits source fragmentation, leading to [M+H]... + The ionic strength increases significantly, such as Figure 1 As shown, in APCI / +H2O, except for L17 (29.1%) and L18 (52.8%), the base peak of all target siloxanes is [M+H]. + ion. Figure 3 The APCI / +H2O mass spectra of the target siloxanes (D4, D9, L4, and L15 as examples) were compared with those obtained under conventional conditions (APCI / −H2O). Therefore, the analytical technique of this invention, which introduces water (APCI / +H2O) as an ionization aid in the ion source, is more favorable for the precursor ion [M+H] of the target analyte. + generate.

[0075] Based on the above, the optimal introduction method of the ionization aid was optimized. Experiments compared two different introduction methods: inserting a capillary tube (with different inner diameters of 0.25 mm, 0.32 mm, 0.53 mm, and 0.9 mm) into the chromatographic vial and leaving the vial open. The results are as follows: Figure 4 As shown, among four methods of extracting the target methylsiloxane [M+H] by introducing the ionization aid (water) via capillary tube, [the results are as follows]. + The peak area response was low, and only L5-L9 of the target siloxanes were detected. In contrast, the open-type method, compared with the four capillary-introduced methods, detected a greater number of target methylsiloxanes and had a higher response.

[0076] Within the APCI source, the remaining volume of the ionization aid decreases continuously with increasing instrument running time. The amount of ionization aid and its stable evaporation directly affect the instrument's analytical capabilities. The experiment optimized the results by using ten initial placement volumes (10 μL, 20 μL, 30 μL, 60 μL, 100 μL, 200 μL, 400 μL, 1000 μL, 1500 μL, and 2000 μL). The experimental results are as follows... Figure 5 As shown, the larger the initial volume of the ionization aid, the greater its evaporation rate. However, when the volume is between 10 μL and 1000 μL, the evaporation rate is similar, around 0.30 μL / min. With an initial ionization aid volume of 1000 μL, evaporation in the ion source continued until only 10 μL remained, a process that took more than 2800 min. Within this time, the evaporation of the ionization aid may be relatively stable. However, since this is an average evaporation rate, further optimization is needed to determine the stability of the volatilization process.

[0077] The ionization aid was initially placed in volumes of 1000 μL, 1500 μL, and 2000 μL, which were then evaporated to 10 μL, with durations in the ion source exceeding 2800 min, 4100 min, and 4800 min, respectively. Based on this, further optimization was conducted to investigate the stability of the ionization aid's volatilization process under different initial volumes. The experiment was optimized across three initial volumes of 1000 μL, 1500 μL, and 2000 μL, with each group of experiments performed in duplicate. The experimental results are as follows: Figure 6 As shown, when the initial placement volume of the ionization aid is 1000 μL, its linear fitting results are better (R0). 2 =0.9991), followed by 1500 μL (R 2 =0.9974, R 2 =0.9941), the worst is 2000μL (R 2 =0.9794, R 2 =0.9838). Figure 6In the linear fitting, the intercept is the theoretical initial placement volume, and the actual initial volumes are 1000μL, 1500μL and 2000μL. The relative deviations between the theoretical and actual initial placement volumes are 1.69%-1.88%, 3.75%-6.22% and 11.0%-12.0%, respectively. The absolute slope of the linear fit was the theoretical evaporation rate. The average theoretical slopes for the three groups (1000 μL, 1500 μL, and 2000 μL) were 0.334 ± 0.004 μL / min, 0.355 ± 0.0104 μL / min, and 0.369 ± 0.0019 μL / min, respectively, while the measured average evaporation rates were 0.38 ± 0.005 μL / min, 0.47 ± 0.022 μL / min, and 0.79 ± 0.024 μL / min, respectively. The relative deviations between the theoretical and measured rates were 10.6%, 24.5%, and 53.3%, respectively. Compared with the three initial placement volumes, the actual evaporation process at an initial placement volume of 1000 μL showed a linear decrease and was more stable. Therefore, the analytical technique of this invention can significantly improve the analysis of the ion abundance of 21 methylsiloxane precursors and provide a stable ionization aid injection environment.

[0078] Comparative Example 2

[0079] This comparative study optimized and reduced the background level of methylsiloxanes during pretreatment and instrumental analysis. Methylsiloxanes were analyzed using gas chromatography-mass spectrometry (GC-MS) with an atmospheric pressure chemical ionization source (APCI / +H₂O) and the mass spectrometry method in MRM mode.

[0080] Before analyzing the concentrated sample (1 mL), it needs to be filtered to prevent contamination from residual particles in the solution that could clog the chromatographic injection port. Syringes with needle filters are a commonly used sample filtration method. In this experiment, two types of syringes—three-piece (with piston) and two-piece (without piston)—were selected, along with four types of needle filters: 0.1 μm nylon membrane, 0.22 μm nylon membrane, 0.22 μm polytetrafluoroethylene membrane, and 0.22 μm polyethersulfone membrane. The combination with the lowest background was selected. Syringe optimization was performed first. In the experiment, 2.5 mL of each syringe (three-piece (with piston) and two-piece (without piston) were used to draw 1 mL of n-hexane before analysis, with six parallel experiments performed for each. The results are as follows: Figure 7As shown in (a) and (b), in hexane drawn using a two-piece (pistonless) syringe, only cyclic siloxanes D4-D9 were detected, but their concentrations were below the instrument's limit of quantitation and could not be quantified, while linear siloxanes were not detected. However, in hexane drawn using a three-piece (piston-equipped) syringe, all but one of the six cyclic methyl siloxanes D4-D9 and fourteen linear methyl siloxanes L5-L18 were detected, with background levels ranging from 17.3±0.40 to 2307±408 ug / L. Among the cyclic methyl siloxanes, D4 had the highest background level, and D5 had the lowest, with a background level range of 43.5±15.6 to 2307±408 ug / L. Figure 7 (a) Among linear methylsiloxanes, L16 had the highest background level, while L5 had the lowest, ranging from 17.3±17.3±0.40 to 1400±171 ng / mL. Comparing the two types of syringes, the three-piece (with piston) syringe introduced significantly more background types and levels than the two-piece (without piston) syringe. Therefore, to avoid high background, a two-piece (without piston) syringe was selected for sample filtration before loading the syringe.

[0081] The background of the needle filter was further investigated using a two-piece (pistonless) syringe. 1 mL of n-hexane was filtered through different needle filters before analysis, with each experiment performed in six parallel runs. Results are as follows: Figure 7 As shown in (c) and (d), the background levels and concentrations varied among filters with different filter media. D4 was below the instrument's detection limit, while D5 was below the instrument's quantitation limit, making quantification impossible. In filters using nylon as the filter media, both cyclic (D5-D9) and linear (L6-L16) methylsiloxanes were detected, with linear methylsiloxanes being predominant. In filters using polytetrafluoroethylene (PTFE) and polyethersulfone (PES) as the filter media, linear methylsiloxanes were not detected; the background was mainly cyclic methylsiloxanes. D6 and D9 were below the instrument's quantitation limit, making quantification impossible. The background level of D7 in the PTFE filter (2.50 ± 0.08 ng / mL) was higher than that in the PES filter, while the opposite was true for D8. Overall, the background levels of the four filters, from highest to lowest, are as follows: 0.22 μm nylon filter > 0.1 μm nylon filter > 0.22 μm polytetrafluoroethylene (PTFE) filter > 0.22 μm polyethersulfone (PES) filter. Although the 0.22 μm PES filter has the lowest overall background level, it is a hydrophilic filter and not suitable for pretreatment with hexane as the extractant. Therefore, the 0.22 μm PTFE needle filter is the optimal choice.

[0082] After sample pretreatment, the samples were stored in chromatographic vials for analysis. Different materials used for the vial caps and septa introduced varying degrees of background as rubber particles entered the sample after the instrument needle punctured the septum. The experiment compared three types of chromatographic caps and septa: blue PTFE / Rsi (blue cap), green PTFE / Rsi (green cap), and PTFE / Butyl rubber (tert-butyl rubber) cap. Six parallel experiments were performed for each type of cap and septum. Results are as follows: Figure 8 As shown in (a) and (b), both blue PTFE / Rsi (blue cap) and green PTFE / Rsi (green cap) septa detected cyclic methylsiloxanes D4-D9, with comparable background concentrations ranging from 4.20 ± 2.41 - 53.8 ± 31.5 ng / mL to 2.42 ± 2.74 - 72.3 ± 58.4 ng / mL. For linear methylsiloxane background, four types (L7-L9 and L12) were detected using the green PTFE / Rsi (green cap), while the blue PTFE / Rsi (blue cap) septa showed significantly higher concentrations. Only L9 was detected in the cap. When using a PTFE / tert-butyl rubber septum cap, neither cyclic nor linear methylsiloxanes were detected, meaning no background introduction was introduced. Therefore, a PTFE / tert-butyl rubber septum cap is the optimal choice, ensuring the chromatographic vial remains airtight while eliminating background introduction.

[0083] The experiment optimized three gas chromatograph inlet septa (Agilent advanced green septa, BTO septa, and Merlin microseal valve septa), with 12 parallel experiments performed for each septa. Results are as follows: Figure 8As shown in (c) and (d), both Agilent advanced green and BTO septa detected cyclic methylsiloxanes D4-D9 with comparable background concentrations, ranging from 12.4±0.95 to 51.9±4.05 ng / mL and 13.0±1.68 to 54.9±7.59 ng / mL, respectively. For linear methylsiloxane background, Agilent advanced green septa detected nine types (L4 and L6-L13) with a background level ranging from 1.10±0.00 to 5.84±0.20 ng / mL, while BTO septa detected three types (L7-L9) with a background level ranging from 3.26±0.39 to 5.38±0.19 ng / mL. However, using a Merlin microseal valve septa resulted in no detection of the target siloxane background. Therefore, the Merlin microseal valve is the best choice.

[0084] The experiment optimized three gas chromatographic capillary columns (DB-5MS, Rxi-5HT, and DB-WAX). Each capillary column was acclimated and then run in six parallel trials. The results are as follows: Figure 8 As shown in (e), the DB-5MS capillary column detected six cyclic methylsiloxanes D4-D9 (0.30±0.22-13.4±7.22 ng / mL) and one linear methylsiloxane L5 (0.92±0.04 ng / mL), while the Rxi-5HT column only detected one linear methylsiloxane, L5 (0.90±0.00 ng / mL). However, using the DB-WAX capillary column, no target methylsiloxane was detected in the background, indicating no background introduction. Therefore, the DB-WAX capillary column is the optimal choice.

[0085] Comparative Example 3

[0086] This comparative example uses a gas chromatography-mass spectrometry system (traditional EI ion source) in SIM mode (Selected Ion Monitor) (GC-EI-MS method) to analyze 21 methylsiloxanes. The instrumental limit of quantitation (LOQ) is compared with that of the GC-APCI-MS / MS method. Results are as follows: Figure 9 As shown, the GC-APCI-MS / MS analysis method has lower sensitivity. Therefore, the analysis technique of this invention is more sensitive.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for analyzing methylsiloxanes based on a GC-APCI-MS / MS method, characterized in that, The method comprises the following steps: The methylsiloxane is analyzed by gas chromatography-mass spectrometry, and the ion source is an atmospheric pressure chemical ionization source; Ultra-pure water is introduced into the ion source as an ionization aid in an open manner; The gas chromatography conditions comprise: The injection port is a non-split injection port, the injection port temperature is 300 DEG C, and the purge flow is 3.0 mL / min; The chromatographic column uses a DB-WAX chromatographic column 15m*0.25mm*0.25um, the carrier gas is high-purity helium, the constant flow mode is used, and the flow is 1.0 mL / min; The temperature rising program is as follows: the initial temperature is 40 DEG C, the temperature is kept for 2 min, the temperature is raised to 255 DEG C at a rate of 15 DEG C / min, the temperature is kept for 8.67 min, and the total time is 25 min; The mass spectrometry conditions comprise: The ion source temperature is 150 DEG C, the auxiliary gas, the cone hole gas, and the supplementary gas are all nitrogen, the flow rates are 200 L / Hr, 50 L / Hr, and 300 mL / min respectively, the APCI positive mode is used, the corona needle current is 0.5 mu A, the cone hole voltage is 30 V, and the mass spectrometry acquisition mode is a multiple reaction monitoring mode.

2. The method of claim 1, wherein, The evaporation rate of the ionization aid is 0.334+ / -0.004 mu L / min, and the evaporation process is linearly decreasing.

3. The method of claim 1, wherein, The method is used for detecting cyclic methylsiloxane and linear methylsiloxane.

4. The method of claim 1, wherein, The cyclic methylsiloxane comprises octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, tetradecamethylcyclotetrasiloxane, hexadecamethylcyclotetrasiloxane or octadecamethylcyclotetrasiloxane; The linear methylsiloxane comprises decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, hexadecamethylheptasiloxane, octadecamethyloctasiloxane, eicosamethylnonasiloxane, docosamethyldesiloxane, tetracosamethyldesiloxane, hexacosamethyldodecasiloxane, octacosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethyldesiloxane, tricosamethy 5. The method of claim 1, wherein, ​ ​ ​ 6. The method of claim 1, wherein, ​ 7. The method of claim 1, wherein, ​ 8. A system for carrying out the method of any one of claims 1 to 7, characterized in that ​ ​ ​ ​ 9. The system of claim 8, wherein, ​

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