General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China Standardization Administration of the People’s Republic of China

Foreword

The national standard was drafted according to the provisions specified in GB/T 1.1-2009.

The national standard was proposed by China National Light Industry Council. It was issued on 31 Dec., 2012, and implemented on 1 Sep., 2012.

The national standard is under the jurisdiction of National Technical Committee 272 on Surfactant and Detergent of Standardization Administration of China (SAC/TC 272).

The national standard was drafted by China Research Institute of Daily Chemical Industry, Guangzhou Startec Science & Technology Co., Ltd., Zhejiang Zanyu Technology Co., Ltd., Productivity Promotion Center of Surfactants and Detergents.

The main drafters of the standard are Feng Yu, Ye Jianzhong, Huang Yaru, Yao Chenzhi, Cheng Xiaojing, Xu Linshou,Xia Xiongyan, Guan Jingcai, Lei Xiaoying.

Determination of chloroacetic acid(chloroacetate) in surfactants Scope

The national standard specifies the methods for determination of mono-chloroacetic acid (monochloroacetate) and di-chloroacetic acid (di-chloroacetate)in surfactants by high performance liquid chromatography(HPLC) method and ion chromatography (IC) method.

The national standard is applicable to surfactants with mono-chloroacetic acid or sodium mono-chloroacetate as raw material, such as alcohol ethoxylated carboxylate(AEC), undecyl imidazoline carboxylate, fatty alkyl dimethyl betaine and fatty acetyl propyl dimethyl betaine, to determine the mono-chloroacetic acid (mono-chloroacetate) and di-chloroacetic acid (di-chloroacetate) content.

When the expected mono-chloroacetic acid(mono-chloroacetate) and/or di-chloroacetic acid (dichloroacetate) content in the test sample is out of the range of the calibration curve, any of following measures is recommended: reduction of test sample mass in sample preparation procedure, dilution of test solution and extra standard solution with appropriate concentration.

Normative references

The GB/T 6682 Water for analytical laboratory use —Specification and test methods and GB/T 13659 Strong acid polystyrene cation exchange resin are indispensable for the application of this document. For dated references,only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

HPLC method

Principle

The sample is dissolved in the acidic acetonitrile solution (10%, 100 mL of acetonitrile + 900 mL of water +2.0 mL of orthophosphoric acid) and analyzed by high performance liquid chromatography (HPLC) with a C8-bonded silica gel column. The mono-chloroacetic acid (mono-chloroacetate) and di-chloroacetic acid (dichloroacetate) are detected by an UV or a PDA detector at 214 nm wavelength.

Reagents

Water, shall conform to grade 1 in accordance with GB/T 6682.

Mono-chloroacetic acid (CH2ClCOOH), AR, purity≥ 99%(w/w).

Di-chloroacetic acid (CHCl2COOH), AR, purity ≥ 99%(w/w).

Acetonitrile (CH3CN), HPLC grade.Orthophosphoric acid (H3PO4), AR.

Hydrochloric acid, 1+1 (V/V) solution.

Mix 10 mL of hydrochloric acid (AR) with 10 mL of water in portions.

Apparatus

Ordinary laboratory apparatus and HPLC instrument,equipped with data processor and a high resolution UV detector or photo diode array detector, of which the noise and the drift of base line at 254 nm is less than 2×10-5AU/s(blank cell) and at 254 nm less than 1×10-3AU/h (blank cell, after stabilizing for 60 min), respectively.

HPLC column, C8-bonded silica gel column (particle size 5 μm), 250 mm×4.6 mm (ID), pH range from 1 to 8;or equivalent.

Micro-syringe, 25 μL.

Analytical balance, reading up to 0.1 mg.

Ultrasonic device for the degassing of reagents.

Filtration device with a vacuum pump, filter membrane with suitable aperture (0.2 μm or 0.45 μm) for the filtration of reagents, and syringe filter head (0.2 μm)for sample filtration before analyzing.

Volumetric flasks, of capacity 100 mL.

Glass beakers, of capacity 50 mL.

Procedure

HPLC conditions. a) Mobile phase: Pipette 2.0 mL of orthophosphoric acid in 900 mL of water, mix and filter with the filtration device. Then, add 100 mL of filtered acetonitrile, and mix well. The pH value of this solution is about 1.7 to 2.0. Before using, the mobile phase should be degassed with an ultrasonic device. b) Flow rate: 1.0 mL/min. c) Detection wavelength: 214 nm.d) Injection volume: 20 μL.

Standard stock solution. Weigh respectively, to the nearest 1×10-4g, 0.1 g of mono-chloroacetic acid and 0.1 g of di-chloroacetic acid, in a 25 mL beaker,add approximately 20 mL of mobile phase, and stir to thoroughly dissolve. Transfer quantitatively to a 100 mL volumetric flask, Dilute to the mark with mobile phase and completely homogenize. This is the standard stock solution with concentration of 1 mg/mL (mono-chloroacetic acid and di-chloroacetic acid, respectively).

Store this standard stock solution in a refrigerator at(4±2) ℃ and renew it every 7 days.

Standard calibration solution. Quantitatively dilute 0.1 mL, 0.5 mL, 1.0 mL, 1.5 mL, 2.0 mL of standard stock solution to 100 mL with mobile phase in 100 mL volumetric flasks, respectively, and mix well. This is the standard calibration solution, which shall be freshly prepared before analysis.

Filter above solutions and inject 20 μL of the filtrate to the HLPC for analysis under the chromatographic conditions. Use appropriate tools or software to calculate the linear correlation coefficient (γ) of the regression curve based on the equation in annex B. The obtained γ shall be 0.999 or above.

Alcohol ethoxylated carboxylate (AEC) and alkyl imidazoline carboxylate sample.Weigh, to the nearest 1×10-4g,5 to 10 g of test sample in a 100 mL beaker, and dissolve with 30 mL of mobile phase, stir until the sample is dissolved completely. Measure the pH with a pH meter and adjust the pH to the value the same as that of mobile phase by adding dropwise HCl solution. Transfer the solution in a 100 mL volumetric flask,rinse the beaker with mobile phase and combine the washing liquid. Dilute to the mark with mobile phase and mix. Filter the test solution with the 0.2 μL syringe filter head and inject 20 μL of the filtrate for analysis under the chromatographic conditions.

Betaine sample. Prepare the sample with ion-exchange column in accordance with the method specified in annex A. Filter the sample solution with syringe filter and inject 20 μL of the filtrate for analysis.

Note: The ion-exchange procedure in the method of annex A is designed to eliminate the interference with the peak of mono-chloroacetic acid or di-chloroacetic acid in betaine chromatogram. Ignore the ion-exchange procedure and prepare the sample solution, if no interference is found in chromatogram.

Chromatogram. Under HPLC, a typical chromatogram is shown in Figure 1.

Figure 1. A typical HPLC chromatogram of monochloroacetic acid and di-chloroacetic acid in fatty alkyl betaine sample

Results and calculation

The mono-chloroacetic acid content, in milligrams per kilogram (mg/kg), is given by the formula (1)

where

X1—is the content, in milligrams per kilogram, of mono-chloroacetic acid.

A —is the concentration, in micrograms per milliliter,of mono-chloroacetic acid in test solution calculated via calibration curve.

V —is the volume, in milliliters, of test solution.

M —is the mass, in grams, of test sample.

The sodium mono-chloroacetate content, in milligrams per kilogram (mg/kg), is given by the formula (2).

where

X2—is the content, in milligrams per kilogram, of sodium mono-chloroacetate.

116.5 —is the molar mass, in grams per mole, of sodium mono-chloroacetate.

94.5 —is the molar mass, in grams per mole, of monochloroacetic acid

The di-chloroacetic acid content, in milligrams per kilogram (mg/kg), is given by the formula (3).

where

X3—is the content, in milligrams per kilogram, of dichloroacetic acid.

B—is the concentration, in micrograms per milliliter,of di-chloroacetic acid in test solution calculated via calibration curve.

The sodium di-chloroacetate content, in milligrams per kilogram (mg/kg), is given by the formula (4).

where

X4—is the content, in milligrams per kilogram, of sodium di-chloroacetate.

150.9—is the molar mass, in grams per mole, of sodium di-chloroacetate.

128.9—is molar mass, in grams per mole, of dichloroacetic acid.

Precision

The absolute difference between two independent single test results, obtained simultaneously or in rapid succession using the same method on identical test sample in the same laboratory by the same analyst using the same apparatus, shall not exceed the repeatability limit(r) in more than 5% of cases. r can be expected to be:

—10% for mono-chloroacetic acid (monochloroacetate) or di-chloroacetic acid (di-chloroacetate)content greater than or equal to 50 mg/kg,

—15% for mono-chloroacetic acid (monochloroacetate) or di-chloroacetic acid (di-chloroacetate)content less than 50 mg/kg.

Ion chromatographic method

Principle

The sample solution is diluted to appropriate concentration and passed through an anion exchange column. The mono-chloroacetic acid (mono-chloroacetate)and di-chloroacetic acid (di-chloroacetate) are adsorbed on the column, then eluted by the mobile phase and detected by the electrical conductivity detector.

Reagents

Ultrapure water, resistivity about 18.2 MΩ.

Mono-chloroacetic acid (CH2ClCOOH), AR, purity ≥99% (w/w).

Di-chloroacetic acid (CHCl2COOH), AR, purity ≥99% (w/w).

Sulfuric acid (H2SO4), AR.

Sodium carbonate (Na2CO3), AR.

Sodium bicarbonate (NaHCO3), AR.

Sodium hydroxide (NaOH), GR.

Apparatus

Ordinary laboratory apparatus and Ion chromatography instrument, equipped with separation column,guard column, appropriate suppressor, data processing software and electrical conductivity detector.

Analytical balance, reading up to 0.1 mg.

Filter membrane, aperture 0.45 μm

Volumetric flasks, of capacity 100 mL and 1, 000 mL.

Glass beakers, of capacity 25 mL and 100 mL.

Procedure

1)Ion chromatographic conditions

General.The choice of chromatographic conditions depends on the apparatus in use and can be varied from those given below, provided that suitable separation of the compounds of interest is maintained.

IC operation condition 1:

Separation column: anion exchange column, suitable for separating mono-chloroacetic acid and di-chloroacetic acid from sample, 4 mm×250 mm, with appropriate guard column.

a) Mobile phase (Eluent solution): a mixture of sodium carbonate and sodium bicarbonate, with 3.2 mmol/L of sodium carbonate and 1.0 mmol/L of sodium bicarbonate,respectively.

b) Flow rate: 0.70 mL/min.

c) Injection volume: 20 μL.

d) Integration mode: peak area.

e) Regeneration solution: 50 mmol/L sulfuric acid aqueous solution.

The limit of detection (signal-to-noise ratio = 3),under above conditions, shall be 0.012 μg/mL for monochloroacetic acid and 0.032 μg/mL for di-chloroacetic acid, respectively.

A typical chromatogram is shown in Figure 2.

Figure 2. A typical IC chromatogram for mono-chloroacetic acid and di-chloroacetic acid (under IC operation conditions 1)

IC operation condition 2:

Separation column: anion exchange column, suitable for separating mono-chloroacetic acid and di-chloroacetic acid from sample, 4 mm×250 mm, with appropriate guard column.

a) Mobile phase (Eluent solution): 15 mmol/L sodium hydroxide solution.

b) Flow rate: 0.85 mL/min.

c) Injection volume: 20 μL.

d) Integration mode: peak area.

The limit of detection (signal-to-noise ratio = 3),under above conditions, shall be 0.012 μg/mL for monochloroacetic acid and 0.051 μg/mL for di-chloroacetic acid, respectively.

A typical chromatogram is shown in Figure 3.

Figure 3. A typical IC chromatogram for mono-chloroacetic acid and di-chloroacetic acid (under IC operation conditions 2)

2)Calibration

Standard stock solution.Weigh respectively, to the nearest 1×10-4g, 0.1 g of mono-chloroacetic acid and 0.1 g of di-chloroacetic acid in a 25 mL beaker, and dissolve in ultrapure water. Transfer quantitatively to a 1, 000 mL volumetric flask, rinse the beaker with ultrapure water and combine the washing liquid. Dilute to the mark and completely homogenize.This is the standard stock solution with concentration of 0.1 mg/mL mono-chloroacetic acid and 0.1 mg/mL di-chloroacetic acid, respectively.

Store this solution in a refrigerator at (4±2)℃ and renew it every 7 days.

Standard calibration solution.Quantitatively dilute 0.1 mL, 0.5 mL, 1.0 mL, 5.0 mL and 10.0 mL of standard stock solution respectively to 100 mL with water in 100 mL volumetric flasks, and mix. This is the standard calibration solution, which shall be freshly prepared before analysis.

Filter the standard calibration solutions with syringe filter head and inject 20 μL of the filtrate each to equipment for analysis under the chromatographic conditions.Use appropriate tools or software to calculate the linear correlation coefficient (γ) of the regression curve based on the equation in annex B. The obtained γ shall be 0.999 or above.

Sampling and analysis.Weigh, to the nearest 1×10-4g, 1 to 5 g of sample in a 25 mL beaker, and dissolve in 30 mL of water, stir until the sample is dissolved completely.Transfer into a 100 mL volumetric flask, rinse the beaker with ultrapure water and combine the washing liquid. Dilute to the mark with water and mix. Filter the solution and inject 20 μL of the filtrate for analysis under appropriate chromatographic conditions.

Results and calculation

1) Mono-chloroacetic acid content

The mono-chloroacetic acid content, in milligrams per kilogram (mg/kg), is given by the formula (5).

where

X5—is the content, in milligrams per kilogram, of mono-chloroacetic acid.

C—is the concentration, in micrograms per milliliter,of mono-chloroacetic acid in test solution calculated via calibration curve.

2) Sodium mono-chloroacetate content

The sodium mono-chloroacetate content, in milligrams per kilogram (mg/kg), is given by the formula (6).

where

X6—is the content, in milligrams per kilogram, of sodium mono-chloroacetate.

3 )Di-chloroacetic acid content

The di-chloroacetic acid content, in milligrams per kilogram (mg/kg), is given by the formula (7).

where

X7— is the content, in milligrams per kilogram, of dichloroacetic acid.

D —is the concentration, in micrograms per milliliter,of di-chloroacetic acid in test solution calculated via calibration curve

4) Sodium di-chloroacetate content

The sodium di-chloroacetate content, in milligrams per kilogram (mg/kg), is given by the formula (8).

where

X8—is the content, in milligrams per kilogram, of sodium di-chloroacetate.

5) Precision

The absolute difference between two independent single test results, obtained simultaneously or in rapid succession using the same method on identical test sample in the same laboratory by the same analyst using the same apparatus, shall not exceed the repeatability limit (r) 15%in rnore than 5% of cases.

Test report

This test report shall contain at least the following information:

a) All information necessary for the complete identification of the test compound；

b) Test method used；

c) All the data (e.g. in tabular form) obtained and the procedure；

d) All operating details not specified in this standard, or regarded as optional, together with details of any incident which may have influenced the test result(s).

Annex A

(Normative)

Pretreatment of Betaine sample

A.1 Principle

Strong acidic cation exchange resin is used to eliminate the interference in betaine sample.

A.2 Reagents

A.2.1 Water, conform to grade 1 specified in GB/T 6682.

A.2.2 Ion exchange resin (GB/T 13659), strong acidic cationic type, in the hydrogen form, 001×7, particle size between 0.3 mm and 1.00 mm.

A.2.3 Hydrochloric acid, AR, 4 mol/L solution.

A.2.4 Extensive pH test paper.

A.2.5 Acetonitrile, HPLC grade, 10% (V/V) water solution: Add 20 mL of acetonitrile to 180 mL of water(A.2.1.), and mix well.

A.3 Apparatus

A.3.1 Volumetric flask, of capacity 100 mL.

A.3.2 Glass beakers, of capacity 200 mL.

A.3.3 Glass exchange column: 25 mm in external diameter and 200 mm in height. The bottom of the column is extended by a narrower glass tube, fitted with a stopcock or is a rubber tube, fitted with a spring clip.

A.4 Procedure

A.4.1 Preparation of cation exchange resin

Soak cation-exchange resin (A.2.2.) in 4 mol/L hydrochloric acid solution (A.2.3). The volume of acid solution should be triple as much as that of the resin. Allow to stand for overnight. Decant the acid and wash the resin three times with water by repeat decantation.

Use another triple volume of hydrochloric acid solution (A.2.3) to soak the resin for 10 min, keep stirring during soaking. Decant the acid, and wash with water thrice by repeat decantation.

Introduce the resin into a preparation column containing a glass-wool plug by means of water. Wash the column with water until the pH of eluate is about 7 (by extensive pH test paper (A.2.4)).

A.4.2 Cation exchange column

Introduce appropriate volume of cation-exchange resin in the analytical column (A.3.3) with a glass-wool plug at the narrower bottom. The height of the resin is about 150 mm. Degassing the column by stir and slight shake. Wash with water until the pH of the eluate reaches 7 approximately (by extensive pH test paper (A.2.4)).Displace the water with 100 mL of acetonitrile solution(A.2.5) at a rate of 1 to 3 mL/min.

A.4.3 Sample preparation

Weigh, to the nearest 1×10-4g, about 5 g of betaine sample in a 200 mL beaker (A.3.2). Add 40 mL of acetonitrile solution (A.2.5) and stir until the sample is dissolved completely.

A.4.4 Sample elution

Pass the sample solution quantitatively through the column at a rate of 1 mL/min, rinse the beaker with appropriate volume of acetonitrile solution (A.2.5) and pass the washing liquid. Add more acetonitrile solution to elute sample. Receive the eluate in a 100 mL volumetric flask (A.3.1) up to the mark. Inject 20 uL after filtration for HPLC analysis.

Annex B

(Informative)

A set of test data is listed in Table B.1.

Table B.1 A set of test data

The linear regression equation (B.1) can be obtained based on the data in Table B.1 by linear regression, also known as least square method.

where

a—constant, slope of linear regression equation,calculated by formula (B.2)

b—constant, intercept of linear regression equation,calculated by formula (B.3)

where

xi—variable of test i

yi—result corresponding to test i

n— total number of tests

—arithmetic mean value of variables of all tests

—arithmetic mean value of corresponding results of all tests

The linear correlation coefficient (γ) of regression equation shall be calculated by formula (B.4)