Quantitative analysis method of main component of insulating medium

Abstract

This invention belongs to the field of component quantitative analysis technology and discloses a quantitative analysis method for the main components of insulating media, including the following steps: S1, extraction and concentration of the sample to be tested; S2, establishment of a multiple reaction monitoring (MRM) analysis method based on GC-MS / MS; S3, detection according to the MRM analysis method to qualitatively confirm each component in the linear alkylbenzene mixed oil; S4, establishment of a standard curve using the external standard method, and calculation of the content of the target component in the sample to be tested using the standard curve. This invention uses GC-MS / MS technology, combined with MRM acquisition mode, retention time and characteristic ion abundance ratio as dual qualitative standards, and establishes a standard curve for quantitative analysis of the target components. The method demonstrates good separation effect, strong anti-interference ability, and accurate analytical results for the main components of the linear alkylbenzene mixed oil.

Description

Technical Field

[0001] This invention relates to the field of quantitative component analysis technology, specifically a method for quantitative analysis of the main components of insulating media. Background Technology

[0002] Insulating media, also known as dielectrics, are insulating materials used to isolate charged conductors. Among them, linear alkylbenzene (LAB) blended oils are a class of high-performance insulating media. Due to their low viscosity, low dielectric loss, high breakdown field strength, and excellent electric field gas evolution properties, they are widely used as impregnating agents and fillers for self-contained high-voltage oil-filled cables and their accessories.

[0003] In linear alkylbenzene blends, dodecylbenzene (DDB) typically accounts for more than 50% of the total composition, with the remainder being alkylbenzene homologues with 10-13 carbon atoms in their side chains. These alkylbenzene homologues with different carbon numbers and substitution positions exhibit subtle differences in physicochemical properties, and their composition directly affects the overall performance of the insulating medium, such as viscosity stability, oxidation resistance, and long-term electrical reliability. Specifically, during long-term cable operation, the insulating medium may undergo aging and degradation due to factors such as heat and electric fields, leading to changes in its compositional structure and thus affecting the safe service life of the cable. Furthermore, when a cable leaks, linear alkylbenzene enters water bodies or soil as an environmental pollutant, and accurate determination of its residual concentration is a crucial indicator for environmental monitoring and risk assessment. Therefore, accurately determining the content of each component in linear alkylbenzene blends is of paramount importance for product quality assessment of cable oils, monitoring the operational status of in-service cables, and assessing potential environmental risks.

[0004] Currently, for the analysis of major components in industrial oil products such as linear alkylbenzene mixtures, existing technologies mostly employ gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS). However, due to the complex composition of linear alkylbenzene mixtures, which include not only homologues with different carbon numbers (C10–C13) but also positional isomers of the benzene ring at different substitution positions on the alkyl chain, GC analysis often results in overlapping or even co-eluting peaks, leading to insufficient resolution and poor analytical accuracy. GC-MS analysis, on the other hand, suffers from significantly increased background noise due to numerous interfering matrix components. Therefore, existing technologies for analyzing the major components of linear alkylbenzene mixtures generally suffer from poor separation, weak anti-interference capabilities, and insufficient sensitivity for quantitative analysis. Summary of the Invention

[0005] The present invention aims to provide a quantitative analysis method for the main components of insulating media to solve the problems in the background art.

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

[0007] A quantitative analysis method for the main components of an insulating medium includes the following steps:

[0008] S1, Sample Pretreatment

[0009] The sample to be tested is extracted and concentrated to obtain the sample solution.

[0010] S2. Establishment of Instrumental Analysis Conditions

[0011] A multi-reaction monitoring and analysis method was established by optimizing the instrument parameters using a gas chromatography-triple quadrupole mass spectrometer.

[0012] S3, Qualitative Analysis

[0013] The sample solution obtained in step S1 is injected into a gas chromatograph-triple quadrupole mass spectrometer and detected according to the multiple reaction monitoring analysis method established in step S2. The components in the sample are qualitatively confirmed by comparing the retention time and characteristic ion abundance ratio of the sample and the standard.

[0014] S4, Quantitative Analysis

[0015] An external standard method was used to establish a standard curve. Based on the chromatographic peak area of ​​the target component in the sample solution, the content of the target component in the sample was calculated using the standard curve.

[0016] Further, in step S1, the sample to be tested is a straight-chain alkylbenzene mixed oil, whose main components include dodecylbenzene and alkylbenzene homologues with 10 to 13 side chain carbon atoms.

[0017] Further, in step S1, the method for extracting and concentrating the sample to be tested is as follows: add dichloromethane to the sample to be tested for liquid-liquid extraction, repeat the extraction multiple times, and combine the extracts; dehydrate the combined extracts with anhydrous sodium sulfate and then concentrate them, and make up to volume with isooctane to obtain the sample solution to be tested.

[0018] Furthermore, the container for holding the sample to be tested is a brown screw-top glass bottle, and the temperature of the concentration process does not exceed 30°C.

[0019] Furthermore, if the extracted solution is dark in color, it can be purified using a syringe filter. The specific method is as follows: draw all the concentrated extract into the syringe, invert the syringe, and wipe away any residue on the needle tip; firmly connect the syringe filter to the needle tip, and filter the extract in the syringe into the sample vial; if necessary, remove the syringe plunger to fill the syringe with air, reconnect the plunger, and press the plunger down to filter the residual sample, thereby maximizing the sample recovery rate.

[0020] Furthermore, in step S2, the conditions for gas chromatography are as follows:

[0021] Inlet temperature: 280~320℃, splitless injection;

[0022] Carrier gas: Helium;

[0023] Column flow rate: 0.8–1.2 mL / min;

[0024] Column temperature: The temperature is programmed to rise. The initial temperature is 50-70℃, held for 1-2 minutes, then increased to 100-130℃ at a rate of 30-50℃ / min, and then increased to 280-320℃ at a rate of 3-8℃ / min, held for 0-5 minutes.

[0025] Furthermore, the conditions for mass spectrometry are:

[0026] Transmission line temperature: 280~320℃;

[0027] Ion source temperature: 280~320℃;

[0028] Color interface temperature: 280~320℃;

[0029] Collision gas: Nitrogen;

[0030] Quenching gas: Helium;

[0031] The data acquisition method was multiple reaction monitoring.

[0032] Furthermore, in step S2, establishing the multiple reaction monitoring analysis method includes the following steps:

[0033] S2.1 Full scan mode analysis: Run the standard in full scan mode to determine the retention time of the target component and select the ion with the highest abundance as the parent ion;

[0034] S2.2 Product ion scanning analysis: The selected parent ion is scanned for product ions under different collision energies, and the characteristic daughter ion with the highest abundance is selected as the daughter ion to form ion pairs;

[0035] S2.3 Collision Energy Optimization: For a given ion pair, operate under different collision cell voltages to optimize the optimal collision energy for each ion pair;

[0036] S2.4 Establish a multiple reaction monitoring and analysis method: Based on optimized ion pairs, collision energies and other mass spectrometry parameters, establish the final multiple reaction monitoring and analysis method.

[0037] Further, in step S3, the conditions for qualitative analysis are: on the chromatogram, the signal-to-noise ratio (S / N) of the chromatographic peak is greater than 3, and the ion pairs monitored in the sample appear within the specified retention time window, with the relative deviation of their ion abundance ratio from the theoretical ion abundance ratio being less than 15%.

[0038] Further, in step S4, the external standard method includes: preparing a series of standard solutions of different concentrations, injecting them into a gas chromatography-triple quadrupole mass spectrometer for analysis, plotting a standard curve with the concentration of the target component as the abscissa and the corresponding peak area as the ordinate; analyzing the sample under the same conditions, finding the corresponding concentration of the target component on the standard curve based on the peak area of ​​the target component in the sample, and calculating the content of the component in the sample.

[0039] The beneficial effects of the technical solution are:

[0040] 1. The method of the present invention uses dichloromethane extraction, anhydrous sodium sulfate dehydration, concentration and volume adjustment and other steps for pretreatment of insulating media (linear alkylbenzene mixed oil), and combines it with needle filter purification and other operations, which can effectively enrich the target components and remove impurities. It also purifies the extract with darker color, further reducing matrix interference and improving the universality and reliability of the analytical method.

[0041] 2. This invention employs gas chromatography-triple quadrupole mass spectrometry (GC-MS) combined with multiple reaction monitoring (MRM) acquisition mode. Through dual screening of precursor and daughter ions, it significantly improves analytical selectivity. Compared with GC and GC-MS, the method of this invention provides better separation, effectively eliminates background interference from complex sample matrices, significantly reduces background noise, avoids false positives, and improves the accuracy of quantitative analysis results.

[0042] 3. The method of this invention, by optimizing mass spectrometry parameters such as ion pairs and collision energies, fully leverages the low-noise advantage of tandem mass spectrometry, significantly improving the signal-to-noise ratio. It can meet the needs of trace detection of cable insulation media and micro-analysis of linear alkylbenzene residues in environmental water samples and soil, providing strong technical support for cable operation status monitoring and environmental risk assessment.

[0043] 4. This invention employs a dual qualitative standard of retention time and characteristic ion abundance ratio, ensuring accurate and reliable qualitative analysis. Simultaneously, it utilizes the external standard method for quantitative analysis, establishing a standard curve to quantitatively analyze the target components. This is further supported by signal-to-noise ratio verification, instrument detection limits, and method detection limits validation, ensuring the accuracy, precision, and repeatability of the quantitative results and meeting the stringent standards for product quality assessment and environmental monitoring. Attached Figure Description

[0044] Figure 1The concentration of linear alkylbenzene components obtained from the measurement and analysis of 5 groups of seawater samples in Example 3 of the present invention. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0046] Example 1: A quantitative analysis method for the main components in an insulating medium (a mixture of linear alkylbenzene oils), using dodecylbenzene standards as the object, to establish and validate the method.

[0047] 1. Instruments and reagents

[0048] Instruments: Agilent 8890-7010B gas chromatograph-triple quadrupole mass spectrometer, equipped with an electron impact (EI) ion source; Column: HP-5MS UI capillary column (30 m × 0.25 mm, film thickness 0.25 μm), stationary phase is 5% phenyl / 95% polymethylsiloxane.

[0049] Reagents: dichloromethane and isooctane (both chromatographic grade, MREADA, USA); anhydrous sodium sulfate (superior grade, Tianjin Kemeio Chemical Reagent Development Center); dodecylbenzene standard (purity ≥98%).

[0050] 2. Preparation of standard solutions

[0051] Accurately weigh an appropriate amount of dodecylbenzene standard, dissolve it in isooctane and dilute to volume to prepare a standard stock solution with a concentration of 100 μg / mL; then dilute it stepwise with isooctane to prepare a series of standard solutions with concentrations of 0.01, 0.02, 0.05, 0.10, 0.20 and 0.50 μg / mL, for a total of 6 mass concentration points.

[0052] 3. Instrumental analysis conditions

[0053] 3.1 Gas Chromatography Conditions

[0054] Inlet temperature: 300℃, splitless injection;

[0055] Carrier gas: High-purity helium (purity ≥99.999%), flow rate 1.0 mL / min (constant flow mode);

[0056] Column oven heating program: Initial temperature 60℃, hold for 1 min; increase to 120℃ at a rate of 40℃ / min; then increase to 300℃ at a rate of 5℃ / min; hold at 300℃ for 3 min.

[0057] 3.2 Mass Spectrometry Conditions

[0058] Transmission line temperature: 300℃;

[0059] Ion source temperature: 300℃;

[0060] Quadrupole temperature: 150℃;

[0061] Ionization method: EI, 70 eV;

[0062] Collision gas: nitrogen, flow rate 1.5 mL / min;

[0063] Quenching gas: Helium, flow rate 2.25 mL / min;

[0064] Data acquisition method: Multiple response monitoring (MRM).

[0065] 4. Establishing the MRM Method

[0066] Precursor ion screening (full scan mode): Run the dodecylbenzene standard solution (1.0 μg / mL) in full scan mode, scanning the range from 50 to 750 u to obtain the mass spectrum. Select characteristic ions with high abundance and a large mass-to-charge ratio (m / z) as precursor ions. For dodecylbenzene, m / z 91 was selected as the quantitative precursor ion.

[0067] Faction ion screening and collision energy optimization (product ion scanning mode): In product ion scanning mode, different collision energies (4, 8, 12, 16, 20, 24, 28, and 32 eV) were set for the selected parent ion to observe the generation of daughter ions. The characteristic daughter ion with the highest abundance was selected as the quantitative daughter ion, and the optimal collision energy was determined to be 20 eV.

[0068] The MRM method is established by setting different collision cell voltages for ion pairs of a given target component, optimizing the optimal collision energy for each daughter ion, and finally using the optimized collision energy while keeping the ion source parameters unchanged.

[0069] 5. Standard curve and detection limit

[0070] Under optimized instrument conditions, a series of standard solutions were sequentially injected and analyzed, with each concentration point analyzed three times. A standard curve was plotted with concentration on the x-axis and the peak area of ​​the quantitative ion pair on the y-axis.

[0071] Example 2: This example uses the analytical method established in Example 1 to analyze the main components of linear alkylbenzenes in a seawater sample from a certain sea area.

[0072] 1. Sample pretreatment

[0073] Seawater samples were collected in accordance with the provisions of GB 17378.3.

[0074] After collecting the sample, accurately measure 1 L of water into a 2 L separatory funnel, add 25 mL of dichloromethane, shake for 2 min, and be careful to release gas. Allow to separate into layers, collect the lower organic phase, and repeat the extraction process twice. Combine the three extracts, dehydrate them through a glass funnel containing approximately 10 g of anhydrous sodium sulfate, and collect the extract in a 100 mL concentration flask. Concentrate to near dryness using a rotary evaporator at 30°C, add isooctane to a final volume of 200 μL, transfer to a sample vial, and store the sample solution at below 4°C until analysis.

[0075] 2. Sample determination

[0076] The processed sample solution was injected into a gas chromatography-triple quadrupole mass spectrometer (GC-MS) under the same analytical conditions as the standard curve for analysis, yielding the MRM chromatogram. In the chromatogram, peaks with a signal-to-noise ratio (S / N) greater than 3 were considered valid peaks.

[0077] The chromatographic peaks detected in the sample were qualitatively confirmed by comparing their retention time (11.50 min) and ion abundance ratio (ratio of quantitative to qualitative ion peak area) with those of the standard. Specifically, the monitored ions were defined as being present within the specified retention time window, and their ion abundance ratio was consistent with the theoretical ion abundance ratio, with a relative deviation of less than 15%. Chromatographic peaks meeting all of these conditions were identified as the target substance.

[0078] 3. Result Calculation

[0079] The external standard method is used for precise quantification of the target substance. The standard sample and the actual sample are injected separately under the same conditions, and the peak areas are compared to determine the quantitative method of the analyte content. Specifically, based on the chromatographic peak area of ​​the target component in the sample, the standard curve equation for dodecylbenzene is substituted, and the concentration of dodecylbenzene in the actual sample solution is calculated according to formula (1).

[0080] (1)

[0081] In the formula, f i For component correction factor; A i Let be the peak area of ​​component i; The content of component i in the standard sample is %.

[0082] Then, based on the concentration factor of the sample, the concentration of dodecylbenzene in the original seawater sample is calculated.

[0083] 4. Spike Recovery Experiment

[0084] Blank seawater samples from the same batch (tested to be free of the target analyte) were used for spiked recovery experiments at three concentration levels: low (0.02 μg / L), medium (0.10 μg / L), and high (0.40 μg / L). Each concentration level was analyzed in six parallel runs. The average recovery rate and relative standard deviation (RSD) were calculated.

[0085] 5. Determination of the method detection limit

[0086] Following all the steps of sample analysis, using blank seawater as the matrix, a blank spiked experiment was conducted with a concentration 3 to 5 times the estimated method detection limit (0.01 μg / L in this example), and 7 parallel determinations were performed. The standard deviation (S) of the 7 parallel determinations was calculated, and the method detection limit was calculated using the detection limit calculation formula (formula (2)) according to the requirements of the "Technical Guidelines for the Formulation and Revision of Environmental Monitoring Analysis Method Standards" (HJ 168).

[0087] (2)

[0088] In the formula, MDL is the method detection limit; n is the number of parallel determinations of the sample; t is the t-distribution (one-sided) with n-1 degrees of freedom and 99% confidence level; S is the standard deviation of n parallel determinations. The t-values ​​for n-1 degrees of freedom and 99% confidence level can be found in Table 1.

[0089] Table 1. t-distribution with n-1 degrees of freedom and 99% confidence level.

[0090]

[0091] That is, when n=7, t （n-1,0.99） =3.143, and the method detection limit for dodecylbenzene in seawater samples was calculated to be 0.008 μg / L.

[0092] Example 3: This example uses the instrumental analysis method established in Example 1 and the sample pretreatment and data analysis method established in Example 2 to analyze the main components of linear alkylbenzenes in 5 groups of seawater samples from a certain sea area.

[0093] Five groups of seawater samples were selected and analyzed using the above method and instrument. The concentrations (ng / L) of the linear alkylbenzene components obtained are shown in Table 2. Figure 1 As shown, the concentrations of C10 to C13 components at each seawater station can be accurately quantified, indicating the feasibility of this method.

[0094] Table 2 Alkylbenzene Composition Table

[0095]

[0096] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A quantitative analysis method for the main components of an insulating medium, characterized in that, Includes the following steps: S1, Sample Pretreatment The sample to be tested is extracted and concentrated to obtain the sample solution. S2. Establishment of Instrumental Analysis Conditions A multi-reaction monitoring and analysis method was established by optimizing the instrument parameters using a gas chromatography-triple quadrupole mass spectrometer. S3, Qualitative Analysis The sample solution obtained in step S1 is injected into a gas chromatograph-triple quadrupole mass spectrometer and detected according to the multiple reaction monitoring analysis method established in step S2. The components in the sample are qualitatively confirmed by comparing the retention time and characteristic ion abundance ratio of the sample and the standard. S4, Quantitative Analysis An external standard method was used to establish a standard curve. Based on the chromatographic peak area of ​​the target component in the sample solution, the content of the target component in the sample was calculated using the standard curve.

2. The method for quantitative analysis of the main components of an insulating medium according to claim 1, characterized in that, In step S1, the sample to be tested is a straight-chain alkylbenzene mixed oil, whose main components include dodecylbenzene and alkylbenzene homologues with 10 to 13 side chain carbon atoms.

3. The method for quantitative analysis of the main components of an insulating medium according to claim 1, characterized in that, In step S1, the method for extracting and concentrating the sample to be tested is as follows: add dichloromethane to the sample to be tested for liquid-liquid extraction, repeat the extraction multiple times, and combine the extracts; The combined extract was dehydrated with anhydrous sodium sulfate and then concentrated, and finally diluted to volume with isooctane to obtain the sample solution to be tested.

4. The method for quantitative analysis of the main components of an insulating medium according to claim 3, characterized in that, The container for holding the sample to be tested is a brown screw-top glass bottle, and the temperature during the concentration process does not exceed 30℃.

5. The method for quantitative analysis of the main components of an insulating medium according to claim 3, characterized in that, If the extracted solution is dark in color, it should be purified using a syringe filter. The specific method is as follows: draw all the concentrated extract into the syringe, invert the syringe, and wipe away any residue from the needle. Securely connect the syringe filter to the needle and filter the extract into the sample vial. If necessary, remove the syringe plunger to fill the syringe with air, reconnect the plunger, and press the plunger down to filter the residual sample, thereby maximizing the sample recovery rate.

6. The method for quantitative analysis of the main components of an insulating medium according to claim 1, characterized in that, In step S2, the gas chromatography conditions are as follows: Inlet temperature: 280~320℃, splitless injection; Carrier gas: Helium; Column flow rate: 0.8–1.2 mL / min; Column temperature: The temperature is programmed to rise. The initial temperature is 50-70℃, held for 1-2 minutes, then increased to 100-130℃ at a rate of 30-50℃ / min, and then increased to 280-320℃ at a rate of 3-8℃ / min, held for 0-5 minutes.

7. The method for quantitative analysis of the main components of an insulating medium according to claim 6, characterized in that, The conditions for mass spectrometry are: Transmission line temperature: 280~320℃; Ion source temperature: 280~320℃; Color interface temperature: 280~320℃; Collision gas: Nitrogen; Quenching gas: Helium; The data acquisition method was multiple reaction monitoring.

8. The method for quantitative analysis of the main components of an insulating medium according to claim 7, characterized in that, In step S2, establishing the multiple reaction monitoring analysis method includes the following steps: S2.1 Full scan mode analysis: The standard is run in full scan mode to determine the retention time of the target component and select the ion with the highest abundance as the parent ion; S2.2 Product ion scanning analysis: The selected parent ion is scanned for product ions under different collision energies, and the characteristic daughter ion with the highest abundance is selected as the daughter ion to form ion pairs; S2.3 Collision Energy Optimization: For a given ion pair, operate under different collision cell voltages to optimize the optimal collision energy for each ion pair; S2.4 Establish a multiple reaction monitoring and analysis method: Based on optimized ion pairs, collision energies and other mass spectrometry parameters, establish the final multiple reaction monitoring and analysis method.

9. The method for quantitative analysis of the main components of an insulating medium according to claim 8, characterized in that, In step S3, the conditions for qualitative analysis are: on the chromatogram, the signal-to-noise ratio (S / N) of the chromatographic peak is greater than 3, and the ion pairs monitored in the sample appear within the specified retention time window, with the relative deviation of their ion abundance ratio from the theoretical ion abundance ratio being less than 15%.

10. The method for quantitative analysis of the main components of an insulating medium according to claim 9, characterized in that, In step S4, the external standard method includes: preparing a series of standard solutions of different concentrations, injecting them into a gas chromatography-triple quadrupole mass spectrometer for analysis, plotting a standard curve with the concentration of the target component as the abscissa and the corresponding peak area as the ordinate; analyzing the sample under the same conditions, finding the corresponding concentration on the standard curve based on the peak area of ​​the target component in the sample, and calculating the content of the component in the sample.

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