Method for determining content of chloroacetic acid by derivatization gas chromatography

Abstract

The invention discloses a derivatization gas chromatography method for determining chloroacetic acid, and belongs to the field of analysis and detection. According to the method, after chloroacetic acid is subjected to derivatization treatment under specific conditions, a DB-624 capillary column is adopted for separation, and a gas chromatography flame ionization detector is adopted for analysis and quantitative treatment of the derivative, so that an analysis result of the content of a to-be-detected product is obtained. The method disclosed by the invention is high in sensitivity, good in repeatability and simple and rapid to operate, can effectively control the product quality, and can be further popularized and applied to analysis and detection of chloroacetic acid in other compounds.

Description

Technical Field

[0001] The present invention belongs to the technical field of pharmaceutical analysis. Specifically, the present invention relates to a derivatization gas chromatography method for the determination of chloroacetic acid. Background Art

[0002] Chloroacetic acid is an important organic chemical raw material, commonly used in the production of pesticides and as an intermediate in organic synthesis. It is also an important carboxymethylating agent with a wide range of uses. Due to its inherent structural characteristics, it may have genotoxicity, so it is extremely important to control its residue level in products. Chloroacetic acid is a white crystalline powder, soluble in water, ethanol, ether, chloroform, and carbon disulfide. Its boiling point is 189 °C, and it has strong corrosiveness, which is likely to damage the instrument and is not convenient for direct injection. Its carboxyl group can be esterified to form volatile esters.

[0003] In China's HG / T 2371-2000, the method for determining the content of industrial chloroacetic acid is titration. In this method, a certain amount of sodium hydroxide is added to chloroacetic acid (containing dichloroacetic acid), and the total chlorine content is measured by argentometry for the generated sodium chloride; the sodium glyoxylate formed by the reaction of dichloroacetic acid with sodium hydroxide and the sodium oxalate formed by the continuous reaction of sodium glyoxylate with sodium hydroxide are titrated with a standard potassium permanganate titrant under appropriate conditions to obtain the content of dichloroacetic acid; the content of chloroacetic acid is obtained by subtracting the content of dichloroacetic acid and the content of free chlorine from the total chlorine content respectively. However, this method has cumbersome operations, long time consumption, and poor accuracy of analysis results. Chloroacetic acid has a simple structure and no conjugated groups, and when determined by liquid chromatography, the ultraviolet response is weak. Gas chromatography has the advantages of fast analysis speed and high sensitivity, but chloroacetic acid has a high boiling point and strong corrosiveness, making it not suitable for direct detection. Summary of the Invention

[0004] To solve the deficiencies of the prior art, the present invention provides a derivatization gas chromatography method for the determination of chloroacetic acid, which greatly improves the detection efficiency of chloroacetic acid in production.

[0005] The present invention provides a derivatization gas chromatography method for the determination of chloroacetic acid, comprising the following steps:

[0006] (1) Preparation of the standard solution: Weigh chloroacetic acid, quantitatively dilute it with absolute ethanol to form a chloroacetic acid solution with a concentration of 15 - 60 μg / ml. Precisely measure 1.0 ml, add thionyl chloride dropwise, heat in a water bath at 50 - 65 °C for 20 - 90 min, cool to room temperature, and then make up the volume to 2.0 ml with dichloromethane to form a standard solution, and calculate the concentration C0 of the formed standard solution.

[0007] (2) Sample treatment: Weigh the weight W of the compound to be measured, add 1.0 ml of absolute ethanol to dissolve it, dropwise add thionyl chloride, heat in a water bath at 50 - 65 °C for 20 - 90 min. After cooling to room temperature, add an appropriate amount of dichloromethane to make the volume up to 2.0 ml, vortex until the sample is completely dissolved, shake well. The volume of dichloromethane for volume determination is S, the sample concentration is 0.1 - 0.3 g / ml, and then inject for analysis;

[0008] (3) Chromatographic conditions: A chromatographic column with 6% cyanopropyl benzene - 94% dimethyl siloxane as the stationary phase; Injection port temperature: 170 - 190 °C; Column flow rate: 2.8 - 3.2 ml / min; Injection mode: Split injection; Temperature programming: The initial column temperature is 75 - 85 °C, and it is heated to 180 °C at a rate of 5 °C per minute; Detector temperature: 210 - 230 °C; Split ratio: 15 - 25:1; 0

[0009] (4) Calculation:

[0010] The content (%) of chloroacetic acid in the sample is calculated according to the following formula:

[0011]

[0012] Where:

[0013] X—the mass fraction of chloroacetic acid in the analyte, expressed as %;

[0014] C0—the concentration of ethyl chloroacetate in the standard solution;

[0015] A—the peak area of ethyl chloroacetate in the analyte;

[0016] A0—the peak area of ethyl chloroacetate in the standard solution;

[0017] S—the dilution volume of the analyte;

[0018] W—the weighed amount of the analyte.

[0019] In the technical solution of the present invention, in step (1), the dropping amount of thionyl chloride is 0.01 - 0.1 ml dropped per milliliter of chloroacetic acid solution.

[0020] In the technical solution of the present invention, in step (1), the dropping amount of thionyl chloride is 0.04 - 0.06 ml dropped per milliliter of chloroacetic acid solution.

[0021] In the technical solution of the present invention, in step (2), the dropping amount of thionyl chloride is 0.1 - 0.5 ml dropped per gram of the sample.

[0022] In the technical solution of the present invention, in step (2), the dropping amount of thionyl chloride is 0.2 - 0.3 ml dropped per gram of the sample.

[0023] In the technical solution of the present invention, the chromatographic column used in step (3) is a DB-624 capillary column.

[0024] In the technical solution of the present invention, the injection volume in step (3) is 0.5 - 1.5 μL.

[0025] In the technical solution of the present invention, the mass of W in step (2) is 0.1 - 0.3 g.

[0026] The present invention can use a common gas chromatograph in the art. For example, the instrument used is as follows: Shimadzu GC2030, equipped with an FID detector.

[0027] The reagents and solvents used in the present invention can be of the purity usually required for gas chromatography. For example: anhydrous ethanol, analytical pure; dichloromethane, analytical pure; thionyl chloride, analytical pure; chloroacetic acid, 98%.

[0028] The instruments used in the determination process of the present invention should be dry, and the solvents are all water-free.

[0029] Beneficial effects: In the detection method of the present invention, after esterification treatment with thionyl chloride - anhydrous ethanol, separation is carried out using a DB-624 capillary column, and chloroacetic acid is detected by a gas chromatograph hydrogen flame ionization detector. The retention time of chloroacetic acid in the standard solution is 8.6 min, with high sensitivity, good precision and accuracy, simple and rapid operation, and it is not easy to cause damage to the metal pipeline of the detection instrument. Description of the Drawings

[0030] Figure 1 It is the chromatogram of the chloroacetic acid reference solution in the embodiment of the present invention;

[0031] Figure 2 It is the chromatogram of the compound to be measured in the embodiment of the present invention;

[0032] Figure 3 It is the linear relationship diagram for determining the content of chloroacetic acid in the embodiment of the present invention. Detailed Embodiments

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. The following described embodiments are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention. After reading the present invention, various equivalent forms of modification by those skilled in the art fall within the scope defined by the appended claims of this application. Those reagents or instruments not indicated by the manufacturer can be conventional products obtained through commercial purchase.

[0034] In the embodiments of the present invention, the sample to be measured used is self-made by the applicant, and the reference substance is obtained through commercial purchase.

[0035] Unless otherwise specified, the instruments, reagents, and solvents used in the following examples are shown in Tables 1 and 2 below.

[0036] Table 1 Instrument Usage

[0037] Instrument Name Model Specification Performance Shimadzu Gas Chromatograph (equipped with FID detector) GC2030 Good

[0038] Table 2 Reagent and Solvent Usage;

[0039] Name Manufacturer Concentration Absolute Ethanol Sinopharm Chemical Reagent Co., Ltd. Analytical Reagent Dichloromethane Sinopharm Chemical Reagent Co., Ltd. Analytical Reagent Thionyl Chloride Sinopharm Chemical Reagent Co., Ltd. Analytical Reagent Chloroacetic Acid MACKLIN 98％

[0040] Unless otherwise specified, the instruments used in the measurement process should be dry, and the solvent should be water-free.

[0041] Example 1

[0042] The chromatographic conditions for this example are as follows: DB-624 capillary column (30m × 0.53mm × 3.0μm), as shown in Table 3 specifically:

[0043] Table 3 Details of Gas Chromatography Condition Parameters

[0044]

[0045] 1. Preparation of standard solution: Weigh chloroacetic acid, quantitatively dilute it with anhydrous ethanol to make a solution containing approximately 60 μg per 1 ml, and shake well. Accurately measure 1.0 ml and place it in a 2-ml volumetric flask, add 1 drop of thionyl chloride (about 0.05 ml), heat in a water bath at 55°C for 60 min, cool to room temperature, and then make up the volume to 2.0 ml with dichloromethane and shake well to form a standard solution, where the concentration of chloroacetic acid is denoted as C0. Inject for analysis, and the chromatogram is as Figure 1 .

[0046] 2. Sample treatment: Weigh 0.2 g (W) of the compound to be tested, accurate to 0.1 mg, place it in a 2-ml (S) volumetric flask, add 1 ml of anhydrous ethanol and 1 drop of thionyl chloride, heat in a water bath at 55°C for 60 min, cool to room temperature, add an appropriate amount of dichloromethane, vortex until the sample is completely dissolved, make up the volume to 2.0 ml with dichloromethane, shake well, inject for analysis, and the chromatogram is as Figure 2 ;

[0047] 3. Sample determination: Determine the sample according to the external standard method of the standard solution, identify it by retention time, and calculate the concentration of chloroacetic acid in the sample by peak area;

[0048] 4. Calculation:

[0049] The content (%) of chloroacetic acid in the sample is calculated according to the following formula:

[0050]

[0051] In the formula:

[0052] X—the mass fraction of chloroacetic acid in the analyte, expressed as %;

[0053] C0—the concentration of chloroacetic acid in the standard solution;

[0054] A—the peak area of ethyl chloroacetate (equivalent to chloroacetic acid) in the analyte;

[0055] A0—the peak area of ethyl chloroacetate (equivalent to chloroacetic acid) in the standard solution read from the instrument;

[0056] S—the dilution volume of the analyte;

[0057] W—the weighed amount of the sample to be analyzed.

[0058] Example 2

[0059] Referring to the method described in Example 1, the sensitivity and precision of the method of the present invention were investigated, and the results are as follows:

[0060] (1) Linear range

[0061] Linear range: the linear range of the solution injected into the instrument is 15.58 - 62.33 μg / ml. Experiments showed that a good linear relationship can be obtained when determining the content of chloroacetic acid by gas-phase derivatization chromatography, such as Figure 3 .

[0062] (2) Detection limit and quantification limit

[0063] Quantification limit solution (15.58 μg / mL): Weigh 12.72 mg of chloroacetic acid reference substance and place it in a 20 ml volumetric flask. Add anhydrous ethanol to dissolve and dilute to the scale, shake well. Pipette 0.5 ml and place it in a 20 ml volumetric flask. Add anhydrous ethanol to about 10 ml, add 1 drop of thionyl chloride, heat in a water bath at 55 °C for 60 min, cool to room temperature, and make up the volume with dichloromethane, shake well.

[0064] Detection limit solution (5.30 μg / mL): Accurately pipette 3 mL of the quantification limit solution into a 10 mL volumetric flask, dilute to the scale with dichloromethane, and shake well.

[0065] The detection limit and quantification limit information of this method are shown in Table 4:

[0066] Table 4 Record table of detection limit and quantification limit data

[0067]

[0068] The results of the precision test of the quantification limit of this method are shown in Table 5:

[0069] Table 5 Record table of precision data of quantification limit

[0070]

[0071] As can be seen from Table 4, the detection limit concentration of chloroacetic acid is 5.30 μg / ml, which is equivalent to 0.005% of the concentration of the test solution, and the signal-to-noise ratio is greater than 3:1; the quantitation limit concentration is 15.58 μg / ml, which is equivalent to 0.016% of the concentration of the test solution, and the signal-to-noise ratio is greater than 10:1. As can be seen from Table 5, at the quantitation limit concentration level, the sample was injected 6 times repeatedly, and the relative standard deviation of the peak areas of each peak in the 6 obtained chromatograms was not greater than 5.0%, indicating good precision in the determination of the quantitation limit.

[0072] Conclusion: This method has high sensitivity and small error, and can be used for quantitative analysis of chloroacetic acid.

[0073] (3) Precision experiment

[0074] The middle concentration within the linear range was continuously injected 6 times under the above conditions, and the results are shown in Table 6.

[0075] Table 6 Results of injection precision test

[0076] Number 1 2 3 4 5 6 Average Peak Area RSD% Peak Area 9605 9656 9811 9877 9839 9835 9771 1.14

[0077] Conclusion: The RSD of the peak area is 1.14%, indicating good injection precision.

[0078] (4) Accuracy experiment

[0079] An appropriate amount of the compound to be tested was taken, and a known concentration of chloroacetic acid reference stock solution was added respectively for derivatization treatment, and then the recovery rate was determined. The results are shown in Table 7.

[0080] Table 7 Record table of accuracy data

[0081]

[0082]

[0083] Conclusion: The recovery rate of chloroacetic acid is between 92.93% and 104.85%, the average value is 98.4%, and the RSD is 4.19%, indicating good recovery.

[0084] Conclusion verification of Example 3

[0085] A certain amount of the compound to be tested was weighed, and after being esterified with absolute ethanol according to the method described in Example 1, it was separated by a DB-624 capillary column, and chloroacetic acid was detected by a gas chromatograph with a hydrogen flame ionization detector. The method has high sensitivity, good precision and accuracy, and is simple and rapid in operation. Chloroacetic acid was not detected in the sample.

[0086] Through method verification, the detection limit, precision and accuracy at each test level meet the expected requirements, as shown in Table 8:

[0087] Table 8 Verification summary

[0088]

[0089] There are no outliers or other situations during the verification process. This method uses a DB-624 capillary column, and the measurement results are stable and accurate. The test detection limit meets the expected requirements and can be selected. This method uses a programmed temperature rise mode for the column temperature, the peak shape of the measurement is better, and the measurement results are stable and accurate, so it can be selected.

Claims

1. A derivatization gas chromatography method for determining chloroacetic acid, characterized in that: The steps include: (1) Preparation of standard solution: Weigh chloroacetic acid and quantitatively dilute it with anhydrous ethanol to prepare a 15-60 μg / ml chloroacetic acid solution. Measure 1.0 ml of the chloroacetic acid solution and dropwise add thionyl chloride. Incubate in a water bath at 50-65°C for 20-90 min. After cooling to room temperature, dilute to 2.0 ml with dichloromethane to form a standard solution. Calculate the concentration C0 of the formed standard solution. (2) Sample treatment: weigh the compound to be tested, add 1.0 ml of anhydrous ethanol to dissolve it, add thionyl chloride dropwise, incubate in a water bath at 50-65°C for 20-90 min, cool to room temperature, add appropriate amount of dichloromethane to make up to 2.0 ml, vortex until the sample is completely dissolved, shake well, the volume of dichloromethane is S, the sample concentration is 0.1-0.3 g / ml, and inject for analysis; (3) Chromatographic conditions: 6% cyanopropylbenzene-94% dimethylsiloxane as stationary phase chromatographic column; injection port temperature: 170-190℃; Column flow rate: 2.8-3.2ml / min; Injection method: split injection; Heating program: Initial column temperature 75-85℃, heating to 180℃ at a rate of 5℃ per minute; Detector temperature: 210-230℃; Split ratio: 15-25:1; (4) Calculation: The content of chloroacetic acid in the sample (%) is calculated as follows: Where: X—mass fraction of chloroacetic acid in the analyte, expressed in %; C0—ethyl chloroacetate concentration in standard solution; A—the peak area of ​​ethyl chloroacetate in the analyte; A0—Ethyl chloroacetate peak area in standard solution; S—dilution volume of the substance to be tested; W—sample weight of the object to be tested.

2. The derivatization gas chromatography method for determining chloroacetic acid according to claim 1, characterized in that: In step (1), the amount of thionyl chloride added is 0.01-0.1 ml per ml of chloroacetic acid solution.

3. The derivatization gas chromatography method for determining chloroacetic acid according to claim 2, characterized in that: In step (1), the amount of thionyl chloride added is 0.04-0.06 ml per ml of chloroacetic acid solution.

4. The derivatization gas chromatography method for determining chloroacetic acid according to claim 1, characterized in that: In step (2), the amount of thionyl chloride added is 0.1 to 0.5 ml per gram of sample.

5. The derivatization gas chromatography method for determining chloroacetic acid according to claim 4, characterized in that: In step (2), the amount of thionyl chloride added is 0.2 to 0.3 ml per gram of sample.

6. The derivatization gas chromatography method for determining chloroacetic acid according to claim 1, characterized in that: The chromatographic column used in step (3) is a DB-624 capillary column.

7. The derivatization gas chromatography method for determining chloroacetic acid according to claim 1, characterized in that: Injection volume in step (3): 0.5-1.5 μL.

8. The derivatization gas chromatography method for determining chloroacetic acid according to claim 1, characterized in that: The mass of W in step (2) is 0.1-0.3 g.

Images