A method for analyzing mercaptoacetic acid isooctyl ester content in an industrial by-product sodium chloride by liquid chromatography

Abstract

This invention belongs to the field of detection, and specifically discloses a liquid chromatography analysis method for the content of isooctyl thioglycolate in sodium chloride, an industrial by-product, including the following steps: sample pretreatment; preparation of standard solution; (3) high performance liquid chromatography detection. This invention uses liquid chromatography to determine the content of isooctyl thioglycolate in sodium chloride solid. This analytical method can accurately detect the content of isooctyl thioglycolate under high salt conditions. The detection limit of isooctyl thioglycolate is 0.4 mg / kg; the quantitation limit of isooctyl thioglycolate is 1.0 mg / kg. This invention has strong specificity, high sensitivity, good recovery rate, accurate and reliable method, and simple operation, and can meet the technical requirements of detection.

Description

Technical Field

[0001] This invention belongs to the field of detection, specifically relating to a liquid chromatography method for analyzing the content of isooctyl thioglycolate in sodium chloride, an industrial byproduct. Background Technology

[0002] 2-Ethylhexyl thioglycolate, an important organic synthesis intermediate and industrial additive, is widely used in the plastics and rubber industries, especially as an auxiliary stabilizer in the heat-stabilized systems of materials such as polyvinyl chloride (PVC). However, this compound has certain toxicity and irritant properties, and may remain as a byproduct or trace impurity in related industrial products (such as sodium chloride byproducts) during the production process, posing potential risks to product quality and safety, environmental protection, and subsequent use. Therefore, establishing an accurate, sensitive, and reliable method for detecting the content of 2-Ethylhexyl thioglycolate is of great significance for the quality control and safety assessment of related industrial byproducts.

[0003] High-performance liquid chromatography (HPLC) is characterized by high separation efficiency, good selectivity, and excellent reproducibility, making it suitable for the qualitative and quantitative analysis of trace organic compounds in complex matrices. This study aims to establish a HPLC-based detection method for the determination of isooctyl thioglycolate in sodium chloride, an industrial byproduct. Through systematic methodological validation, the method was ensured to meet analytical requirements in terms of specificity, sensitivity, linearity, precision, repeatability, and accuracy, providing reliable technical support and standardized operating procedures for the detection of practical samples. Summary of the Invention

[0004] To address the aforementioned problems, this invention discloses a liquid chromatography method for analyzing the content of isooctyl mercaptoacetate in sodium chloride, an industrial byproduct.

[0005] This invention is achieved through the following technical solution: A liquid chromatography method for the analysis of isooctyl thioglycolate content in sodium chloride, an industrial byproduct, includes the following steps: (1) Sample pretreatment: Add extraction reagent to the sample, mix, vibrate and sonicate, and filter; (2) Prepare standard solutions; (3) High performance liquid chromatography detection.

[0006] Furthermore, the extraction reagent was a mixture of ethyl acetate and acetonitrile in a volume ratio of 4:1.

[0007] Furthermore, the specific process of sample pretreatment is as follows: Take 1.00 g of sodium chloride solid as test sample, place it in a 10 mL centrifuge tube, add 2.0 mL of ethyl acetate-acetonitrile (4:1, v / v) mixed extraction solution, vortex for 10 min, sonicate for 20 min, and filter the supernatant through a 0.22 μm filter membrane.

[0008] Furthermore, the preparation process of the standard solution is as follows: accurately weigh 10 mg of isooctyl mercaptoacetate standard, place it in a 100 mL volumetric flask, dilute to the mark with acetonitrile solution, shake well, and prepare a 1 mL isooctyl mercaptoacetate standard solution containing 100 μg, which is the reference stock solution; take 0.5 mL of the reference stock solution, accurately measure it, place it in a 10 mL volumetric flask, dilute to the mark with acetonitrile, shake well, and prepare a 1 mL solution containing 5.0 μg, which is the standard solution.

[0009] Furthermore, the chromatographic column was an Agilent 5 TC-C18 with dimensions of 250 mm × 4.6 mm and a diameter of 5 μm; the injection volume was 20 μL; the column temperature was 30 ℃; the flow rate was 1.0 mL / min; the mobile phase was acetonitrile: 0.05% phosphoric acid aqueous solution = 70:30 (v / v); isocratic elution was performed from 0 to 20 min; and the wavelength was 210 nm.

[0010] Beneficial effects This invention provides an analytical method for determining the content of isooctyl mercaptoacetate in solid sodium chloride using liquid chromatography. This method can accurately detect the content of isooctyl mercaptoacetate under high-salt conditions, with a detection limit of 0.4 mg / kg and a quantitation limit of 1.0 mg / kg. This invention features high specificity, high sensitivity, good recovery, accuracy, reliability, and simple operation, meeting the technical requirements for detection. Attached Figure Description

[0011] Figure 1 Chromatogram of a dilution solvent blank; Figure 2 The chromatogram of the test solution; Figure 3 The chromatogram is of the reference solution; Figure 4 The chromatogram of the spiked solution of the test sample; Figure 5 The working curve of the method. Detailed Implementation

[0012] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available reagents and materials.

[0013] Example 1 1. Instruments and Materials 1.1 Experimental Apparatus Shimadzu SPD-20A liquid chromatograph (Shimadzu Corporation, Japan); Agilent 5 TC-C18 column (250 mm × 4.6 mm, 5 μm) (Agilent Technologies, USA); KQ-250E CNC ultrasonic cleaner (Shanghai Chubo Experimental Equipment Co., Ltd.); Mettle XS204 electronic balance (Mettler Instruments, Switzerland).

[0014] 1.2 Experimental Materials Reference standard isooctyl mercaptoacetate (batch number I96059) was purchased from Alta; ethyl acetate and acetonitrile were chromatographically pure and purchased from Tiandi Inc., USA; phosphoric acid was analytically pure and purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.; Wahaha purified water was ordered from a supermarket; and a sample of sodium chloride solid, a byproduct of a certain factory, was also provided.

[0015] 2 Experimental Methods 2.1 Chromatographic conditions The chromatographic column was an Agilent 5 TC-C18 (250 mm × 4.6 mm, 5 μm). The injection volume was 20 μL, the column temperature was 30℃, and the flow rate was 1.0 mL / min. The mobile phase was acetonitrile: 0.05% phosphoric acid aqueous solution = 70:30 (v / v). Isocratic elution was performed from 0 to 20 min at a wavelength of 210 nm.

[0016] 2.2 Solution Preparation Preparation of the test solution: Weigh 1.00 g of sodium chloride solid and place it in a 10 mL centrifuge tube. Add 2.0 mL of ethyl acetate-acetonitrile (4:1, v / v) mixed extraction solution, vortex to dissolve the acetonitrile, shake for 10 min, sonicate for 20 min, and filter the supernatant through a 0.22 μm filter membrane to obtain the test solution.

[0017] Preparation of reference stock solution: Accurately weigh 10 mg of isooctyl mercaptoacetate standard, place it in a 100 mL volumetric flask, dilute to the mark with acetonitrile solution, shake well, and prepare a 1 mL standard solution containing 100 μg of isooctyl mercaptoacetate.

[0018] Preparation of reference solution: Take 0.5 mL of the reference stock solution, accurately measure it, place it in a 10 mL volumetric flask, dilute to the mark with acetonitrile, shake well, and prepare a solution containing 5.0 ug in 1 mL.

[0019] 2.3 Results and Discussion 2.3.1 Selection of Extraction Solvent System An ethyl acetate-acetonitrile (4:1, v / v) mixed extract can effectively extract isooctyl mercaptoacetate. This invention investigated the extraction of ethyl acetate, acetonitrile, ethyl acetate-acetonitrile (1:1, v / v), ethyl acetate-acetonitrile (2:1, v / v), ethyl acetate-acetonitrile (3:1, v / v), ethyl acetate-acetonitrile (4:1, v / v), and ethyl acetate-acetonitrile (5:1, v / v).

[0020] Isooctyl mercaptoacetate (SMA) is a moderately lipophilic ester compound. Ethyl acetate alone is too weakly polar, highly volatile, and has poor compatibility with the mobile phase. Acetonitrile alone is insufficient in its solubility for the target compound and struggles to overcome salt matrix adsorption. When ethyl acetate or acetonitrile is used alone, the recovery rate of SMA drops below 90%. This experiment used this extraction solvent to extract SMA. Ethyl acetate provides strong ester solubility, while acetonitrile adjusts polarity, improves wettability, and enhances chromatographic compatibility. In a high-salt sodium chloride system, it forms a strengthened salting-out effect, effectively blocking matrix adsorption and achieving efficient and stable extraction of the target compound. As the proportion of ethyl acetate in the mixed system increases, the solubility and desorption efficiency of the target compound gradually improve, and the recovery rate increases accordingly. When the ratio is ethyl acetate:acetonitrile (4:1, v / v), the optimal balance is achieved in solubility, salting-out effect, matrix desorption, and chromatographic compatibility, with the recovery rate exceeding 95%. Further increasing the proportion of ethyl acetate leads to excessively low system polarity, decreased wettability, increased volatility, and poorer chromatographic compatibility, resulting in a decrease in the recovery rate. Therefore, this experiment selected an ethyl acetate to acetonitrile volume ratio of 4:1 as the optimal extraction solvent.

[0021] 2.3.2 Selection of Mobile Phase To achieve rapid extraction of isooctyl mercaptoacetate, the mobile phases selected were acetonitrile-water, acetonitrile-0.05% phosphoric acid aqueous solution, and acetonitrile-0.1% phosphoric acid aqueous solution. During isocratic elution, the peak shape of isooctyl mercaptoacetate was affected when using acetonitrile-water, resulting in a lower recovery rate. The recovery rate increased significantly when using acetonitrile-0.05% phosphoric acid aqueous solution, but then began to decrease again.

[0022] The mobile phase utilizes a weakly acidic environment to inhibit the dissociation and ester bond hydrolysis of isooctyl mercaptoacetate, ensuring its stable molecular state retention on the C18 column and guaranteeing detection accuracy and stability. Phosphorylation of silanol groups eliminates secondary adsorption, significantly improving peak shape, avoiding tailing, and enhancing column efficiency and resolution. Acetonitrile provides suitable reversed-phase elution capability, working in conjunction with the aqueous phase to achieve efficient separation of the target analyte from matrix impurities and eliminate interference from the sodium chloride matrix. This system exhibits low UV absorption, a stable baseline, and low noise at 210 nm, significantly improving detection sensitivity and meeting trace quantification requirements. A phosphoric acid concentration of 0.05% is the optimal acidity, achieving the best balance between inhibiting dissociation, protecting the column, and improving peak shape.

[0023] 3. Analytical Method Validation 3.1 Specificity Verification Acetonitrile was used as the extraction solution and the test solution for injection to demonstrate that the blank extraction solution and other impurities in the test solution did not interfere with the analyte testing. The reference solution and the spiked test solution were also injected. The corresponding spectra are shown below. Figures 1-4 As shown in the figure, the extraction solution does not interfere with the detection of the target compound, and other impurities in the sample do not interfere with the detection of the target compound, indicating that the method has strong specificity.

[0024] 3.2 Validation of Limit of Quantitation and Limit of Detection The concentration with a signal-to-noise ratio (S / N) of 3 to 5 is the limit of detection concentration; the concentration with a S / N of 10 to 15 is the limit of quantitation concentration, and the relative standard deviation of the S / N corresponding to the limit of quantitation for 6 needles should be ≤10.0%.

[0025] Accurately transfer 0.4 mL of the reference solution into a 10 mL volumetric flask, dilute to the mark with acetonitrile to prepare a 200 ng / mL solution, which will be used as the detection limit verification concentration.

[0026] Accurately transfer 1.0 mL of the reference solution into a 10 mL volumetric flask, dilute to the mark with acetonitrile to prepare a 500 ng / mL solution, which will be used as the limit of quantitation verification concentration.

[0027] The test results are shown in Tables 1 and 2.

[0028] Table 1 Detection Limit Experiment Results Table 2 Results of Limit of Quantitation Experiment The results showed that the detection limit of isooctyl mercaptoacetate in this analytical method was 0.4 mg / kg; the quantitation limit of isooctyl mercaptoacetate was 1.0 mg / kg, and the relative standard deviation of the signal-to-noise ratio of the 6-needle quantitation limit was 2.78%, which was less than 10%.

[0029] 3.3 Linearity Range Verification Take an appropriate amount of the reference stock solution and serially dilute it with acetonitrile solution to prepare standard solutions with concentrations of 500 ng / mL, 1000 ng / mL, 2000 ng / mL, 5000 ng / mL, 10000 ng / mL, and 20000 ng / mL, as linearity range validation solutions. Inject 20 μL of each of the above solutions and record the working curves. (See figure) Figure 5 The linearity results for the compounds are shown in Tables 3 and 4.

[0030] Table 3. Results of linear experiments Table 4. Linear results of isooctyl mercaptoacetate The results showed that the linear equation for isooctyl mercaptoacetate in the analytical method was y = 3.861x + 645.1 with a linear correlation coefficient R² = 0.999 in the mass concentration range of 500–20000.0 ng / mL, indicating a good linear relationship.

[0031] 3.4 Method Precision Validation The reference solution was used as the method precision test solution, and the injection was repeated 6 times. The peak area response values ​​were recorded, and the relative standard deviation was calculated. The results showed that the relative standard deviation of the peak area of ​​isooctyl mercaptoacetate in this analytical method was 3.36%, proving that the method has high precision.

[0032] Table 5. Results of Method Precision Test 3.5 Repeatability Validation Accurately weigh 1.00 g of sodium chloride and place it in a 10 mL centrifuge tube. Then, accurately add 0.1 mL of isooctyl thioglycolate (SHT) reference stock solution, followed by 1.90 mL of an ethyl acetate:acetonitrile (4:1) mixture. Vortex for 10 min, then sonicate for 20 min. Collect the supernatant to obtain a mixed solution containing an SHT standard concentration of 5.0 μg / mL. This solution was used as the repeatability test solution. Six parallel samples were prepared, with 20 μL injected from each sample. The measured concentrations were recorded, and the relative standard deviations (RSDs) were calculated. The RSDs of the measured concentrations of the analyte in the six parallel samples were 3.95%. Table 6 shows that the repeatability of SHT in this analytical method is good.

[0033] Table 6 Repeatability Test Results 3.6 Spike Recovery Validation Accurately weigh 1.00 g of sodium chloride and place it in a 10 mL centrifuge tube. Then, accurately add 0.08 mL of isooctyl thioglycolate (SHS) reference stock solution, followed by 1.92 mL of an ethyl acetate:acetonitrile (4:1) mixed solution. Vortex for 10 min, then sonicate for 20 min. Collect the supernatant to obtain a mixed solution containing an SHS standard concentration of 4.0 μg / mL. Prepare three aliquots of this solution. Alternatively, accurately weigh 1.00 g of sodium chloride and place it in a 10 mL centrifuge tube. Then, accurately add 0.10 mL of isooctyl thioglycolate (SHS) reference stock solution, followed by 1.90 mL of an ethyl acetate:acetonitrile (4:1) mixed solution. Vortex for 10 min, then sonicate for 20 min. Collect the supernatant to obtain a solution containing an SHS standard concentration of 5.0 μg / mL. Three aliquots of a mixed solution containing 100% isooctyl thioglycolate (IOS) standard were prepared. 1.00 g of sodium chloride was accurately weighed and placed in a 10 mL centrifuge tube. Then, 0.12 mL of IOS stock solution was accurately added, followed by 1.88 mL of an ethyl acetate:acetonitrile (4:1) mixed solution. The mixture was vortexed for 10 min, then sonicated for 20 min. The supernatant was collected to obtain a mixed solution containing 6.0 ug / mL IOS, which was then used as a 120% IOS test solution. Three aliquots of this solution were prepared. The recovery rate and relative standard deviation of the IOS content were calculated. The difference between the measured results and the true values ​​was verified to determine whether the analytical method could obtain accurate test results. The IOS spiked recovery test results are shown in Table 7.

[0034] Table 7 Results of the recovery rate test of isooctyl mercaptoacetate The results showed that the recoveries of isooctyl mercaptoacetate in this analytical method ranged from 88.1% to 94.0% at low, medium, and high spikes, with a relative standard deviation of 2.14%, indicating good recovery results.

[0035] 3.7 Sample Content Determination Sodium chloride solid samples (samples 1, 2, and 3) from a certain factory were taken. 1.00 g of sodium chloride was accurately weighed and placed in a 10 mL centrifuge tube. 2.0 mL of an ethyl acetate:acetonitrile (4:1) mixed solution was then accurately added. The tubes were vortexed for 10 min, followed by sonication for 20 min. 20 μL of the supernatant was collected from each sample and injected. The results are shown in Table 8.

[0036] Table 8 Sample Test Results Table 8 Sample test results 4. Conclusion The verification of the above indicators shows that the analytical method for determining the content of isooctyl thioglycolate in sodium chloride solid using high-performance liquid chromatography has high specificity, high sensitivity, good recovery rate, accuracy, reliability, and simple operation, and can meet the technical requirements for detection.

Claims

1. A liquid chromatography method for analyzing the content of isooctyl thioglycolate in sodium chloride, an industrial byproduct, characterized in that, Includes the following steps: (1) Sample pretreatment: Add extraction reagent to the sample, mix, vibrate and sonicate, and filter; (2) Prepare standard solutions; (3) High performance liquid chromatography detection.

2. The method according to claim 1, characterized in that, The extraction reagent was a 4:1 volume ratio of ethyl acetate to acetonitrile mixed solution.

3. The method according to claim 1, characterized in that, The specific process of sample pretreatment is as follows: Take 1.00 g of sodium chloride solid as test sample, place it in a 10 mL centrifuge tube, add 2.0 mL of ethyl acetate-acetonitrile (4:1, v / v) mixed extraction solution, vortex for 10 min, sonicate for 20 min, and filter the supernatant through a 0.22 μm filter membrane.

4. The method according to claim 1, characterized in that, The chromatographic column was an Agilent 5 TC-C18, with dimensions of 250 mm × 4.6 mm and a diameter of 5 μm; the injection volume was 20 μL; the column temperature was 30 °C; the flow rate was 1.0 mL / min; the mobile phase was acetonitrile: 0.05% phosphoric acid aqueous solution = 70:30 (v / v); isocratic elution was performed from 0 to 20 min; and the wavelength was 210 nm.

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