CN112305144A

CN112305144A - Method for measuring dichloroacetic acid and trichloroacetic acid in water by ion chromatography

Info

Publication number: CN112305144A
Application number: CN201910693212.5A
Authority: CN
Inventors: 游咏妍
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-07-30
Filing date: 2019-07-30
Publication date: 2021-02-02

Abstract

The invention relates to a method for measuring dichloroacetic acid and trichloroacetic acid in water by ion chromatography, which comprises the following steps: adopting dichloroacetic acid and trichloroacetic acid standard solutions which all use methyl tert-butyl ether AS solvents, selecting an AS19 analytical column and an AG19 protective column, setting the column temperature at 23 ℃, enabling KOH eluent to enter an ion chromatography detection system in a gradient elution mode, and obtaining a linear equation of peak area and mass concentration. And calculating the content of dichloroacetic acid and trichloroacetic acid in water by a linear equation. The method is simple and convenient to operate, improves the separation degree of a nitrite chromatographic peak and a dichloroacetic acid chromatographic peak, and enables the determination of dichloroacetic acid to be more accurate.

Description

Method for measuring dichloroacetic acid and trichloroacetic acid in water by ion chromatography

Technical Field

The invention relates to the determination of dichloroacetic acid and trichloroacetic acid, and belongs to the field of chemical analysis.

Background

One of the currently used methods for measuring dichloroacetic acid and trichloroacetic acid in water is CJ/T141-2018 ion chromatography, the column temperature is constant to 30 ℃, but practice shows that under the condition of the column temperature of 30 ℃, a nitrite chromatographic peak is close to a dichloroacetic acid chromatographic peak, so that the measurement of the dichloroacetic acid is interfered. The temperature has little influence on the determination of trichloroacetic acid. The method adopts the solid standard products of dichloroacetic acid and trichloroacetic acid, needs balance and pure water for dissolution, and has troublesome operation.

Disclosure of Invention

The present invention aims at overcoming the demerits of available technology, and provides one kind of method suitable for measuring dichloroacetic acid and trichloroacetic acid in water.

The purpose of the invention can be realized by the following technical scheme: a method for measuring dichloroacetic acid and trichloroacetic acid in water by ion chromatography is characterized in that a dichloroacetic acid and trichloroacetic acid standard solution which both use methyl tert-butyl ether as a solvent is adopted. Although methyl tert-butyl ether is slightly water-soluble in nature, the intermediate solution for preparing dichloroacetic acid and the standard solution for trichloroacetic acid are both 100 times diluted with pure water, and the proportion of methyl tert-butyl ether in pure water is only 1%, so that methyl tert-butyl ether can be fused with water in a short time, and the methyl tert-butyl ether does not form interference peaks in ion chromatographic analysis and has no influence on the determination of dichloroacetic acid and trichloroacetic acid in water. The method comprises the following steps: and (3) measuring the peak area of the sample filtered by the 0.22-micron filter membrane by adopting an ion chromatograph, and comparing the peak area with a standard curve to obtain the concentrations of dichloroacetic acid and trichloroacetic acid in the sample to be measured. The ion chromatograph is characterized in that an AS19 analytical column and an AG19 protective column are selected AS chromatographic columns, an ASRS anion suppressor is used AS a suppressor, the column temperature is 23 ℃, the suppression current is 124mA, the sample injection volume is 500 mu L, the eluent is potassium hydroxide solution, the flow rate of the eluent is 1.0mL/min, gradient elution is carried out, and the determination is completed within 50 minutes. Wherein the gradient elution conditions are: 0-40 min: 6 mmol/L; 40-45 min: 50 mmol/L; 45-50 min: 6 mmol/L.

The standard curve is prepared by dissolving dichloroacetic acid and trichloroacetic acid standard solutions, which all use methyl tert-butyl ether as a solvent, in pure water to prepare a standard series solution. According to the sanitary Standard for Drinking Water (GB 5749-2006), the limit value of dichloroacetic acid is 0.05mg/L, and the limit value of trichloroacetic acid is 0.1 mg/L, the concentration of the standard series solution is set as follows: the mass concentrations of the dichloroacetic acid are respectively 0.02mg/L, 0.04mg/L, 0.05mg/L, 0.07mg/L, 0.12mg/L and 0.16 mg/L; the mass concentrations of trichloroacetic acid were 0.05mg/L, 0.10mg/L, 0.15mg/L, 0.20mg/L, 0.30mg/L, and 0.40mg/L, respectively, and the mixed standards were subjected to ion chromatography using an anion detection mode to obtain calibration curves of the mass concentrations and peak areas of dichloroacetic acid and trichloroacetic acid, respectively.

Compared with the prior art, the invention has the following advantages:

(1) the separation degree of a nitrite chromatographic peak and a dichloroacetic acid chromatographic peak is improved, so that the determination of the dichloroacetic acid is more accurate.

(2) The operation is simple and convenient, and the labor time is saved.

Drawings

FIG. 1 is an ion chromatogram of dichloroacetic acid and nitrite standards under column temperature conditions 1.

FIG. 2 is an ion chromatogram of dichloroacetic acid and nitrite standards under column temperature condition 2.

FIG. 3 is an ion chromatogram of dichloroacetic acid and trichloroacetic acid standards under optimal detection conditions.

FIG. 4 is an ion chromatogram of a standard sample of dichloroacetic acid and trichloroacetic acid added to tap water under optimal detection conditions.

Detailed Description

The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the present invention.

The required instruments are DIONEX AQUION ion chromatograph, conductivity detector, AS19 (250 mm. times.4 mm) anion analytical column, AG19 (50 mm. times.4 mm) anion guard column, ASRS anion suppressor.

Required reagents: nitrogen as carrier gas with purity greater than or equal to 99.999%, potassium hydroxide leacheate (Thermo).

Standard substance: standard solutions of dichloroacetic acid (1003. + -. 10.63 mg/L) and trichloroacetic acid (990. + -. 5.68 mg/L) in methyl tert-butyl ether (MTBE) and/or MTBE) were purchased from O2si, USA. Nitrite nitrogen standard solution (100 mg/L), Ministry of environmental protection Standard samples research institute.

1. Determination of optimal conditions: a standard mixture of dichloroacetic acid and nitrite each having a concentration of 0.16mg/L was prepared using pure water, and subjected to ion chromatography under the same conditions except for different column temperatures. Under the conditions of inhibiting current 124mA, sample injection volume of 500 mu L, eluent flow rate of 1.0mL/min, gradient elution (eluent concentration of 0-40 min: 6 mmol/L; 40-45 min: 50 mmol/L; 45-50 min: 6 mmol/L), column temperature condition 1: the column temperature is 30 ℃; column temperature condition 2: the column temperature was 23 ℃. Considering the separation degree of dichloroacetic acid and nitrite, the optimal detection conditions are that the column temperature is 23 ℃, the inhibiting current is 124mA, the sample injection volume is 500 mu L, the flow rate of the eluent is 1.0mL/min, gradient elution is carried out, and the concentration of the eluent is 0-40 min: 6 mmol/L; 40-45 min: 50 mmol/L; 45-50 min: 6 mmol/L.

2. Preparation of standard solution: dichloroacetic acid intermediate solution (ρ =10.03 mg/L): 1.00mL of a dichloroacetic acid standard solution (1003. + -. 10.63 mg/L) using methyl tert-butyl ether as a solvent was accurately transferred to a 100mL volumetric flask, and the volume was determined by pure water and mixed. Storing at 0-4 ℃. Dichloroacetic acid standard use solution (ρ =1.00 mg/L): 10.0mL of the intermediate dichloroacetic acid solution (. rho =10.03 mg/L) was accurately transferred to a 100mL volumetric flask and the volume was determined by pure water. It is prepared immediately after use. Trichloroacetic acid standard use solution (ρ =9.90 mg/L): 1.00mL of trichloroacetic acid standard solution (990. + -. 5.68 mg/L) using methyl tert-butyl ether as a solvent was accurately transferred to a 100mL volumetric flask and the volume was fixed with pure water. It is prepared immediately after use.

3. Drawing a standard curve: 1.00mL, 2.00mL, 2.50mL, 3.50mL, 6.00mL, 8.00mL of a dichloroacetic acid standard solution (. rho =1.00 mg/L) and 0.25mL, 0.50mL, 0.75mL, 1.00mL, 1.50mL, 2.00mL of a trichloroacetic acid standard solution (. rho =9.90 mg/L) were taken out of 6 50mL volumetric flasks, and the volume was fixed with pure water. In this standard series of solutions: the mass concentrations of the dichloroacetic acid are respectively 0.02mg/L, 0.04mg/L, 0.05mg/L, 0.07mg/L, 0.12mg/L and 0.16 mg/L; the mass concentration of the trichloroacetic acid is 0.05mg/L, 0.10mg/L, 0.15mg/L, 0.20mg/L, 0.30mg/L and 0.40mg/L respectively. Sequentially carrying out computer measurement under the optimal detection condition according to the sequence of the concentration from low to high. The response value (peak area) of the target compound chromatographic peak is taken as the ordinate, the corresponding mass concentration is taken as the abscissa, a standard curve is drawn, and the linear range and the linear correlation coefficient are shown in table 1.

TABLE 1 Linear Range and correlation coefficient of test items

Detecting items	Linear Range (mg/L)	Linear equation of equations	Correlation coefficient
				Dichloroacetic acid	0.02~0.16	Y=1.422x-0.0034	0.9996
Trichloroacetic acid	0.05~0.40	Y=1.061x-0.011	0.9996

4. Precision: under the best detection conditions, the pure water spiked samples of three different concentrations were determined in parallel seven times, and the data obtained are shown in table 2.

TABLE 2 precision of the results of the dichloroacetic acid and trichloroacetic acid measurements

5. Accuracy: under the best detection condition, pure water and tap water standard samples with three different concentrations are measured, and the recovery rate is shown in table 3.

TABLE 3 accuracy of the dichloroacetic acid and trichloroacetic acid measurements

Claims

1. A method for measuring dichloroacetic acid and trichloroacetic acid in water by ion chromatography is characterized in that dichloroacetic acid and trichloroacetic acid standard solutions which use methyl tert-butyl ether as solvents are adopted, although methyl tert-butyl ether is slightly soluble in water, intermediate solutions for preparing dichloroacetic acid and standard use solutions for preparing trichloroacetic acid are both 100 times diluted by pure water, the proportion of methyl tert-butyl ether in the pure water is only 1%, therefore, the methyl tert-butyl ether can be fused with water in a short time, and the methyl tert-butyl ether does not form interference peaks in the ion chromatography analysis, and does not influence the dichloroacetic acid and the trichloroacetic acid in the measured water,

the method comprises the following steps: and (2) measuring the peak area of the sample filtered by the 0.22 mu m filter membrane by adopting an ion chromatograph, and comparing the peak area with a standard curve to obtain the concentration of dichloroacetic acid and trichloroacetic acid in the sample to be measured, wherein the ion chromatograph is under the conditions that an AS19 analytical column is selected AS a chromatographic column, an AG19 protective column is selected AS an inhibitor, an ASRS anion inhibitor is adopted AS the inhibitor, the column temperature is 23 ℃, the inhibiting current is 124mA, the sample injection volume is 500 mu L, the eluent is potassium hydroxide solution, the flow rate of the eluent is 1.0mL/min, gradient elution (0-40 min: 6 mmol/L; 40-45 min: 50 mmol/L; 45-50 min: 6 mmol/L) is carried out, and the measurement is completed within 50 minutes.

2. The method of claim 1, wherein the column temperature is 23 ℃, the chromatographic peak of the chloride ion with higher concentration covers the chromatographic peak of the dichloroacetic acid at low temperature, and the chromatographic peak of the nitrite is close to the chromatographic peak of the dichloroacetic acid at high temperature, thereby interfering with the determination of the dichloroacetic acid.

3. The method for measuring dichloroacetic acid and trichloroacetic acid in water by ion chromatography as claimed in claim 1, wherein the standard curve is prepared by dissolving dichloroacetic acid and trichloroacetic acid standard solutions, both of which use methyl tert-butyl ether as a solvent, in pure water to prepare a standard series of solutions: the mass concentrations of the dichloroacetic acid are respectively 0.02mg/L, 0.04mg/L, 0.05mg/L, 0.07mg/L, 0.12mg/L and 0.16 mg/L; the mass concentrations of trichloroacetic acid were 0.05mg/L, 0.10mg/L, 0.15mg/L, 0.20mg/L, 0.30mg/L, and 0.40mg/L, respectively, and the mixed standards were subjected to ion chromatography using an anion detection mode to obtain calibration curves of the mass concentrations and peak areas of dichloroacetic acid and trichloroacetic acid, respectively.