GB/T 3051-2025General methods for the determination of chloride content in inorganic chemical products — Mercurimetric method and ion chromatography method (English PDF)

5.1 Principle

In slightly acidic water or ethanol solution, a strongly ionized mercuric nitrate standard titration solution is used to convert chloride ions into weakly ionized mercuric chloride, and diphenylcarbazone indicator solution is used to react with excess Hg2+ to form a purple-red complex to determine the endpoint.

5.2 Reagents or materials

5.2.1 Nitric acid solution. 1+19.

5.2.2 Sodium hydroxide solution. 40 g/L.

5.2.3 Mercuric nitrate standard titration solution I. c[1/2Hg(NO3)2]~0.1 mol/L.

5.2.4 Mercuric nitrate standard titration solution II. c[1/2Hg(NO3)2]~0.01 mol/L, c[1/2Hg(NO3)2]~0.005 mol/L, c[1/2Hg(NO3)2]~0.001 mol/L. Accurately dilute the mercuric nitrate standard titration solution I by the required multiple. During dilution, add an appropriate amount of nitric acid solution (1+1) to prevent hydrolysis of the mercuric nitrate.

5.2.5 Bromophenol blue indicator solution (0.4 g/L).

5.2.6 Diphenylcarbazone indicator solution (0.25 g/L).

5.3 Instruments and equipment

Microburette. The graduation value is 0.01 mL or 0.02 mL.

5.4 Test steps

5.4.1 Preparation of test solution

Weigh an appropriate amount of specimen to the nearest 0.0002 g. Treat using an appropriate method, or transfer an appropriate amount of test solution after chemical treatment (so that interfering ions do not exceed the specified limits, see Appendix A; chlorine content is 0.01 mg~80 mg). Place the solution in a conical flask, controlling the total volume to 100 mL~200 mL (if titrating in ethanol, the total volume shall not exceed 40 mL, with a volume ratio of ethanol to water of 3:1). Add 4~5 drops of bromophenol blue indicator solution (0.4 g/L), and adjust the pH of the test solution to 2.5~3.5 by following one of the following procedures.

-- If the test solution is yellow, add sodium hydroxide solution until the test solution turns blue, then add nitric acid solution until the test solution just turns yellow, and then add more 2~6 drops (in the case of ethanol solution, add more 2~3 drops);

-- If the test solution is blue, add nitric acid solution until the test solution is just yellow, and then add more 2~6 drops (in the case of ethanol solution, add more 2~3 drops).

5.4.2 Test

Add 1 mL of diphenylcarbazone indicator solution (0.25 g/L) to the test solution and titrate with a mercuric nitrate standard titration solution of appropriate concentration (see Appendix B) until the color of the test solution changes from yellow to purple-red, that is, the end.

At the same time, a blank test is also performed. Except that no sample is added to the blank test solution, the types and amounts of other reagents added (except the standard titration solution) are the same as those of the test solution.

NOTE 1: During determination, the limits and elimination of some ions that do not interfere with the determination, ions that interfere with the determination, and co-existing interfering substances are shown in Appendix A and Appendix C, respectively.

NOTE 2: Collect and retain the mercury-containing waste liquid after titration. See Appendix D for treatment methods.

5.5 Experimental data processing

The chloride content is expressed as the mass fraction w of chloride (as Cl) and is calculated according to formula (1).

Where:

V -- the volume of the mercuric nitrate standard titration solution consumed in the titration of the test solution, in milliliters (mL);

V0 -- the volume of the mercuric nitrate standard titration solution consumed in the titration of the blank test solution, in milliliters (mL);

c -- the exact value of the concentration of the mercuric nitrate standard titration solution, in moles per liter (mol/L);

M -- the molar mass of chlorine (Cl), in grams per mole (g/mol) (M=35.45);

m -- the mass of the specimen, in grams (g).

6.1 Principle

The test solution enters the anion exchange column and is eluted with the eluent.

Chloride ions in the test solution undergo ion exchange on the anion exchange column and are carried to the detector by the eluent, forming a Gaussian-distribution chromatographic peak. The peak area/height of chloride (as Cl) within a certain concentration range is proportional to the component concentration, allowing the chloride content to be determined.

6.2 Reagents or materials

6.2.1 Chloride standard solution. 1 mL of solution contains 0.01 mg of chlorine (Cl).

Pipette 1.00 mL of the chloride standard stock solution (as Cl) prepared according to HG/T 3696.2 into a 100 mL volumetric flask. […]