A method for determining industrial methyl perfluoroisobutylate by gas chromatography

Abstract

The application discloses a method for determining industrial methyl perfluoroisobutyrate by gas chromatography, adopts a 60m capillary column with a stationary phase of (6% -cyanopropyl-phenyl) methyl polysiloxane, and cooperates with a specific programmed temperature condition and a headspace sampling mode to simultaneously separate three impurities of dimethyl carbonate, perfluoroisobutyryl fluoride and methyl perfluoropropionate, the resolution of each component is greater than 1.5, and the quantitative detection limit of dimethyl carbonate is less than or equal to 0.05%. The application realizes quantitative detection by a blank correction standard curve method, has the characteristics of strong separation capacity, high sensitivity, good precision and simple operation, and is suitable for multi-component synchronous quality detection of industrial methyl perfluoroisobutyrate products.

Description

Technical Field

[0001] This invention relates to the field of instrumental analysis technology, specifically to a gas chromatographic qualitative and quantitative determination method for industrial-grade perfluoroisobutyrate methyl ester. Background Technology

[0002] Methyl perfluoroisobutyrate is a high-performance fluorinated chemical and an important chemical intermediate raw material. In industrial production, it has excellent dielectric properties, a wide boiling point range, outstanding material compatibility and thermal stability. It can be used as a cold cleaning agent, a special solvent and a reaction medium, and is widely used in liquid cooling and heat transfer fields.

[0003] Currently, my country lacks a unified testing standard for perfluoroisobutyrate methyl ester. The conventional gas chromatography methods used by various manufacturers generally suffer from two major drawbacks: first, they can only detect dimethyl carbonate as a single impurity, failing to simultaneously separate fluorinated homologues such as perfluoroisobutyryl fluoride and perfluoropropionate methyl ester, resulting in poor multi-component separation and significant deviations in quantitative results; second, the direct injection method is susceptible to sample volatility, leading to poor injection repeatability and high detection limits, failing to meet the quantitative requirements for trace impurities. The quality control of industrial-grade products lacks standardized, accurate, and efficient methods for simultaneous multi-component detection. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing methods for detecting perfluoroisobutyrate (PFOS) such as weak impurity separation capability, high detection limit, and poor repeatability. This invention provides a gas chromatographic method for the determination of industrial PFOS, achieving baseline separation of the main component from various fluorinated impurities. It features simple operation, high sensitivity, and excellent precision and accuracy, making it suitable for rapid quality testing of industrial products.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A gas chromatographic method for the determination of industrial-grade perfluoroisobutyrate methyl ester. The steps of the measurement method are as follows: Preparation of standard samples: Add different masses of dimethyl carbonate standard to methyl perfluoroisobutyrate standard, mix well to obtain a series of standard samples with gradient concentrations; at the same time, take pure methyl perfluoroisobutyrate standard as blank control sample. Chromatographic detection: Each standard sample and blank control sample were injected and analyzed under the same chromatographic conditions, and the retention time and corresponding peak area of ​​methyl perfluoroisobutyrate and each impurity were recorded. Standard curve plotting: A standard curve is plotted with the content of dimethyl carbonate as the abscissa and the correction peak area as the ordinate; the correction peak area is the peak area of ​​dimethyl carbonate in the standard sample minus the peak area of ​​dimethyl carbonate in the blank control sample. Test sample detection: The industrial perfluoroisobutyrate sample to be tested was subjected to gas chromatography analysis under the same conditions. The measured peak area of ​​dimethyl carbonate was substituted into the standard curve to calculate the content of dimethyl carbonate and perfluoroisobutyrate in the sample. Gas chromatography was used for qualitative and quantitative determination of methyl perfluoroisobutyrate. The core chromatographic conditions are as follows: Chromatographic column: Capillary column with (6% cyanopropyl-phenyl)methylpolysiloxane as stationary phase, 60 m × 0.32 mm × 1.0 μm; Programmed temperature ramp: Initial column temperature 40℃, hold for 15 min; ramp to 200℃ at a rate of 10℃ / min, hold for 10 min.

[0006] Furthermore, the detector is a flame ionization detector (FID) with a detector temperature set at 230°C; the carrier gas is high-purity nitrogen with a flow rate of 1.5 mL / min; the split ratio is set at 50:1; and the vaporization chamber temperature is set at 230°C.

[0007] Furthermore, headspace sampling was employed, with a headspace equilibrium temperature of 60℃ and an equilibrium time of 15 min. The sample was filtered through a 0.22 μm organic phase filter before headspace injection, with a single injection volume of 0.5–2.0 μL. This injection method avoids injection errors for volatile samples and improves detection repeatability and sensitivity.

[0008] Preferably, a total of 4 standard sample series are prepared, each containing 100g of perfluoroisobutyrate methyl ester standard, and the amount of dimethyl carbonate added is 0.2g, 0.5g, 0.8g, and 1.5g, respectively; the standard samples are prepared in pressure-resistant reagent bottles, first adding perfluoroisobutyrate methyl ester standard, then adding dimethyl carbonate standard, and mixing thoroughly.

[0009] Under the above chromatographic conditions, baseline separation of three impurities—dimethyl carbonate, perfluoroisobutyryl fluoride, and perfluoropropionate—from the main component can be achieved simultaneously, with a resolution greater than 1.5 for each component and a limit of quantification of dimethyl carbonate ≤0.05%.

[0010] This invention, through a combination of specific chromatographic column selection, optimized temperature programming, and headspace injection, achieves baseline separation of methyl perfluoroisobutyrate from various fluorinated impurities, offering the following advantages: 1. Strong separation capability: It can simultaneously separate three typical process impurities, and the separation degree of each meets the baseline separation requirements, solving the industry pain point of insufficient separation degree of multiple impurities in conventional methods.

[0011] 2. High sensitivity: Headspace injection combined with a long column and thick liquid film design results in a detection limit of less than 0.05% for dimethyl carbonate, which is far superior to conventional direct injection methods and can meet the needs of trace impurity detection.

[0012] 3. High precision and fast detection speed: High sample repeatability, controllable single sample detection cycle, suitable for rapid screening and quality control of industrial batch samples.

[0013] 4. Easy to operate: No complicated pretreatment is required, the sample volume is small, the detection cost is low, it is compatible with conventional gas chromatographs, and it is easy to promote and apply in industrial enterprises. Attached Figure Description

[0014] Figure 1 The gas chromatogram of the mixed sample under the chromatographic conditions of this invention is labeled with four chromatographic peaks: perfluoroisobutyryl fluoride, methyl perfluoropropionate, dimethyl carbonate, and methyl perfluoroisobutyryl fluoride, and their corresponding resolution values. Figure 2 This is the gas chromatogram of pure methyl perfluoroisobutyrate; Figure 3 The gas chromatogram of pure dimethyl carbonate is shown. Figure 4 The standard curve for dimethyl carbonate is shown, with linear correlation coefficients and limits of detection labeled. Figure 5 This is a comparative chromatogram of a conventional 30m column, used to demonstrate the separation advantage of this method. Detailed Implementation

[0015] The technical solution of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can fully and accurately understand and implement the present invention.

[0016] Example 1 Instruments and reagents Instrument: Fuli F80 gas chromatograph, equipped with a flame ionization detector and headspace sampler.

[0017] Reagents: Methyl perfluoroisobutyrate standard (content ≥98%, Shanghai Aladdin Biochemical Technology Co., Ltd.); dimethyl carbonate standard (content ≥99%, Shanghai Linen Technology Development Co., Ltd.); perfluoroisobutyryl fluoride standard; methyl perfluoropropionate standard.

[0018] Gas chromatography conditions The chromatographic conditions are shown in the table below: Capillary column: (6%-cyanopropyl-phenyl)methylpolysiloxane fused silica column, column length 60 m × column inner diameter 0.32 mm × stationary phase liquid film thickness 1.0 μm; Column temperature program: Hold at 40℃ for 15 min, then increase the temperature to 200℃ at a rate of 10℃ / min and hold for 10 min; Vaporization chamber temperature: 230℃; Detector type: FID flame ionization detector; Detector temperature: 230℃; Flow split ratio: 50:1; Carrier gas flow rate (nitrogen): 1.5 mL / min; Make-up gas flow rate (nitrogen): 30 mL / min; Hydrogen flow rate: 30 mL / min; Air flow rate: 300 mL / min Headspace equilibration conditions: Equilibrate at 60℃ for 15 minutes; Injection volume: 1.0 μL; Preparation of standard samples: Accurately weigh 100g of perfluoroisobutyrate methyl ester standard (accurate to 0.0002g) into 100mL pressure-resistant reagent bottles, and add 0.2g, 0.5g, 0.8g, and 1.5g of dimethyl carbonate standard in sequence. After shaking well, four standard samples with gradient concentrations are obtained.

[0019] Determination and Standard Curve Establishment: 1 μL of each standard sample was injected for analysis, with pure perfluoroisobutyrate standard used as a blank control. The correction peak area was obtained by subtracting the dimethyl carbonate peak area of ​​the blank control from the peak area of ​​the standard sample. A standard curve was plotted with dimethyl carbonate content on the x-axis and correction peak area on the y-axis.

[0020] The test results showed that the retention time of perfluoroisobutyryl fluoride was approximately 8.3 min, that of methyl perfluoropropionate was approximately 9.7 min, that of methyl perfluoroisobutyryl fluoride was approximately 11.8 min, and that of dimethyl carbonate was approximately 20.9 min. The separation degree between each pair of components was greater than 1.5, achieving baseline separation. Within the dimethyl carbonate content range of 0.2%-1.5%, the linear correlation coefficient R0 was [not specified]. 2 =0.9998, and the limit of detection was 0.042%.

[0021] Example 2: Precision Verification The standard sample containing 0.2g of dimethyl carbonate from Example 1 was measured six times in parallel according to the above detection method. The peak area of ​​dimethyl carbonate was recorded and the content was calculated. The results are shown in the table below:

[0022] The experimental results show that the relative standard deviation of the dimethyl carbonate content detection method is 3.58%, which is of good precision and meets the requirements of industrial quantitative detection.

[0023] Example 3: Actual Sample Testing Two commercially available industrial perfluoroisobutyrate methyl products were used as test samples. The samples were analyzed under the chromatographic conditions described in Example 1. The content of dimethyl carbonate was calculated by substituting its peak area into the standard curve. The detection status of each impurity was recorded. The results are shown in the table below:

[0024] The results show that this method can accurately quantify the content of the main component and various impurities in industrial samples, and is suitable for comprehensive quality control of perfluoroisobutyrate products.

[0025] Comparative Example 1: Comparison of Conventional Chromatographic Columns Using the same model instrument, but replacing the column with a 30m × 0.32mm × 0.5μm column of the same type, and with all other conditions consistent with Example 1, the same mixed sample was analyzed. The results showed that the peaks of perfluoroisobutyryl fluoride and perfluoropropionate partially overlapped, with a resolution of only 0.9, making accurate quantification impossible; the limit of detection for dimethyl carbonate was 0.12%, which was significantly lower than the sensitivity of the present invention.

[0026] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A gas chromatographic method for the determination of industrial-grade perfluoroisobutyrate methyl ester, characterized in that, Includes the following steps: (1) Add different masses of dimethyl carbonate standard to methyl perfluoroisobutyrate standard, mix evenly, and obtain a series of standard samples containing dimethyl carbonate; at the same time, use pure methyl perfluoroisobutyrate standard as blank control sample. (2) Gas chromatography analysis was performed on each standard sample and blank control sample to obtain the retention time and peak area of ​​methyl perfluoroisobutyrate and dimethyl carbonate. (3) Plot a standard curve of dimethyl carbonate content versus correction peak area, wherein the correction peak area is the peak area of ​​dimethyl carbonate in the standard sample minus the peak area of ​​dimethyl carbonate in the blank control sample. (4) Perform gas chromatography analysis on the perfluoroisobutyrate sample to be tested, and substitute the measured peak area of ​​dimethyl carbonate into the standard curve of step (3) to obtain the content of perfluoroisobutyrate and dimethyl carbonate in the sample. The chromatographic conditions for the gas chromatography used to determine methyl perfluoroisobutyrate include: The chromatographic column is a capillary column, the stationary phase of which is 6% cyanopropylphenylmethylpolysiloxane, the column length is 60m, the column inner diameter is 0.32mm, and the stationary phase liquid film thickness is 1.0μm; The temperature program conditions in the determination method are as follows: initial column temperature 40℃, hold for 15 min; then increase the temperature to 200℃ at a rate of 10℃ / min, hold for 10 min; The determination method simultaneously separates three impurities in the sample: dimethyl carbonate, perfluoroisobutyryl fluoride, and perfluoropropionate. The separation degree of each component from the main component is greater than 1.

5.

2. The gas chromatography determination method according to claim 1, characterized in that, The detector used in the determination method is a hydrogen flame ionization detector with a detector temperature of 230℃.

3. The gas chromatography determination method according to claim 1, characterized in that, The carrier gas used in the determination method is nitrogen, and the carrier gas flow rate is 1.5 mL / min.

4. The gas chromatography determination method according to claim 1, characterized in that, The split ratio is 50:

1.

5. The gas chromatography determination method according to claim 1, characterized in that, The temperature of the vaporization chamber is 230℃.

6. The gas chromatography determination method according to claim 1, characterized in that, The sample was introduced via headspace, with a headspace equilibrium temperature of 60℃ and an equilibrium time of 15 min. The sample was filtered through a 0.22 μm organic phase filter membrane before headspace injection, with an injection volume of 0.5-2 μL.

7. The gas chromatography determination method according to any one of claims 1-6, characterized in that, The limit of detection for dimethyl carbonate is ≤0.05%.

8. The gas chromatography determination method according to claim 7, characterized in that, In step (1), four standard samples are prepared. Each standard sample contains 100g of perfluoroisobutyrate methyl standard, with the amount of dimethyl carbonate added being 0.2g, 0.5g, 0.8g, and 1.5g, respectively.

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