HJ 585-2010Water quality. Determination of free chlorine and total chlorine. Titrimetric method using N, N-diethyl-1, 4-phenylenediamine (English PDF)

4.1 Determination of free chlorine

At pH 6.2-6.5, free chlorine and N,N-diethyl-1,4-phenylenediamine (DPD) form a red compound with ferrous sulfate the ammonium standard solution was titrated until the red color disappeared.

4.2 Determination of total chlorine

At pH 6.2-6.5, elemental chlorine, hypochlorous acid, hypochlorite and chloramine react with DPD in the presence of excess potassium iodide.

The red compound was titrated to a red color with a standard solution of ammonium ferrous sulfate.

5.1 Interference from other chlorine compounds

Chlorine dioxide interferes with the determination of free chlorine and total chlorine, and chlorite interferes with the determination of total chlorine. Chlorine dioxide and chlorite it can be corrected by measuring its concentration. For the determination method, see GB/T 5750.11 and GB/T 5750.10.

High concentrations of monochloramine interfere with the determination of free chlorine. Can be added by adding sodium arsenite solution (6.13) or thioacetamide solution (6.13) Elimination of interference with monochloramine, determination of monochloramine in accordance with Appendix A.

5.2 Correction of interference between manganese oxide and hexavalent chromium

Manganese oxide and hexavalent chromium can interfere with the determination. The interference can be eliminated by measuring the concentration of manganese oxide and hexavalent chromium.

5.3 Interference of other oxides

This method interferes in the presence of the following oxidizing agents. bromine, iodine, bromoamine, iodine, ozone, hydrogen peroxide, chromate, oxidation Manganese, hexavalent chromium, nitrite, copper ions (Cu2) and iron ions (Fe3). Among them Cu2 (6 reagents and materials Unless otherwise stated, analytically pure reagents that meet national standards were used for the analysis.

6.1 Experimental water. It is deionized water or double distilled water containing no chlorine and reducing substances. The experimental water needs to pass the inspection before it can be used.

Test method. Add 100 ml of water to be tested and 1.0 g of potassium iodide (6.4) to the first 250 ml Erlenmeyer flask and mix. After 1 min, Add 5.0 ml buffer solution (6.11) and 5.0 ml DPD test solution (6.12); then add 100 ml to the second 250 ml Erlenmeyer flask to be tested.

Water and 2 drops of sodium hypochlorite solution (6.6). After 2 min, 5.0 ml buffer solution (6.11) and 5.0 ml DPD test solution (6.12) were added.

The first bottle should not be colored, and the second bottle should be pink. Otherwise, the experimental water should be dechlorinated by activated carbon treatment and pressed.

The steps are checked for quality and can be used until qualified.

6.2 Concentrated sulfuric acid. rho = 1.84 g/ml.

6.3 orthophosphoric acid. rho = 1.71 g/ml.

6.4 Potassium iodide. crystal.

6.5 Sodium hydroxide solution. c (NaOH) = 2.0 mol/L

Weigh 80.0 g of sodium hydroxide and dissolve in 500 ml of water (6.1). After the solution is cooled, transfer it to a 1 000 ml volumetric flask and add water (6.1).

Go to the marking line and mix.

6.6 Sodium hypochlorite solution. rho(Cl2)~0.1 g/L

It is diluted by a concentrated solution of sodium hypochlorite (trade name, Antifumin).

6.7 Potassium dichromate standard solution. c (1/6K2Cr2O7) = 100.0 mmol/L

Accurately weigh 4.904 g of finely divided potassium dichromate (baked at 105 ° C for more than 2 h), dissolved in a 1 000 ml volumetric flask, and added water (6.1) Go to the marking line and mix.

6.8 Ammonium ferrous sulfate stock solution. c[(NH4)2Fe(SO4)2·6H2O]~56 mmol/L

Weigh 22.0 g of ferrous ammonium hexahydrate, dissolved in water (6.1) containing 5.0 ml of concentrated sulfuric acid (6.2), and transferred to 1 000 ml of brown.

In the volumetric flask, add water (6.1) to the mark and mix. Calibration is performed before measurement.

Calibration method. Add 50.0 ml of ferrous ammonium sulfate stock solution (6.8) and 5.0 ml of orthophosphoric acid (6.3) to a 250 ml Erlenmeyer flask.

And 4 drops of diphenylamine sulfonate indicator solution (6.10). Titrate with potassium dichromate standard solution (6.7) until dark green, the color of the solution remains unchanged Time is the end point. The concentration of this solution is expressed in millimoles of chlorine (Cl2) per liter, and is calculated according to the formula (1).

twenty two

c Vc

Where. c1-- ferrous sulfate ammonium stock solution concentration, mmol/L;

C2--concentration of potassium dichromate standard solution, mmol/L;

V2--the volume of the potassium dichromate standard solution consumed by titration, ml;

V1--the volume of ferrous ammonium sulfate stock solution, ml;

2--Ethylene ferrous ammonium sulfate corresponds to the number of moles of chlorine (Cl2).

Note. If V2 is less than 22 ml, the ammonium ferrous sulfate stock solution should be reconstituted.

6.9 Ammonium ferrous sulfate standard titration solution. c[(NH4)2Fe(SO4)2·6H2O]~2.8 mmol/L

Take 50.0 ml of ferrous ammonium sulfate stock solution (6.8) in a 1 000 ml volumetric flask, add water (6.1) to the mark, mix and store in brown in the reagent bottle. Available now.

The concentration c3 (mmol/L) of this solution is expressed in millimoles of chlorine (Cl2) per liter, and is calculated according to the formula (2).

Cc = (2)

6.10 Diphenylamine sulfonate indicator solution. rho[(C6H5-NH-C6H4-SO3)2Ba]=3.0 g/L

Weigh 0.30 g of diphenylamine sulfonate dissolved in a 100 ml volumetric flask, add water (6.1) to the mark, and mix.

6.11 Phosphate buffer solution. pH=6.5

Weigh 24.0 g of anhydrous sodium hydrogen phosphate (Na2HPO4) or 60.5 g of disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), and 46.0 g potassium dihydrogen phosphate (KH2PO4), dissolved in water, and added 100 ml of 8.0 g/L disodium EDTA dihydrate (C10H14N2O8Na2·2H2O) solution or 0.8 g EDTA disodium solid, transfer to a 1 000 ml volumetric flask, add water (6.1) to the mark, Mix well. If necessary, 0.020 g of mercuric chloride can be added to prevent mold propagation and interference with traces of iodide in the reagents to the free chlorine test.

6.12 N,N-diethyl-1,4-phenylenediamine sulfate (DPD) solution. rho[NH2-C6H4-N(C2H5)2·H2SO4]=1.1 g/L

2.0 ml of concentrated sulfuric acid (6.2) and 25 ml of 8.0 g/L dihydrate EDTA disodium solution or 0.2 g EDTA disodium solid, Add 250 ml of water (6.1) to prepare a mixed solution. Add 1.1 g of anhydrous DPD sulfate or 1.5 g of pentahydrate to the above mixture in solution, transfer to a 1 000 ml brown volumetric flask, add water (6.1) to the mark and mix. The solution was placed in a brown reagent bottle and stored at 4 °C.

If the solution changes color after standing for a long time, it should be reconstituted.

Note. DPD sulphate can also be replaced by 1.1 g DPD oxalate or 1.0 g DPD hydrochloride.

6.13 sodium arsenite solution, rho (NaAsO2) = 2.0 g/L; or thioacetamide solution, rho (CH3CSNH2) = 2.5 g/L.

8.1 Sample Collection

Free chlorine and total chlorine are unstable and samples should be determined on site as much as possible. If the sample cannot be measured on site, the sample should be stored with a fixative.

Pre-add the sample volume 1% NaOH solution (6.5) to the brown glass bottle, collect the water sample to fill the sample bottle, and immediately cover the plug.

And sealed to avoid contact with air. If the sample is acidic, increase the amount of NaOH solution added to ensure that the pH of the water sample is >12.

8.2 Sample storage

The water samples were transported in a freezer, stored in a laboratory at 4 ° C, protected from light, and measured within 5 days.

9.1 Preparation of samples

Take 100 ml of the sample as sample V0. If the total chlorine (Cl2) exceeds 5 mg/L, take a smaller volume and dilute with water (6.1).

100 ml.

9.2 Determination of free chlorine

In a 250 ml Erlenmeyer flask, add 15.0 ml of phosphate buffer solution (6.11), 5.0 ml of DPD solution (6.12) and sample (9.1).

Mix well. Immediately titrate to the colorless end with ammonium ferrous sulfate standard titration solution (6.9), and record the number of milliliters of the titration solution volume V3.

For samples containing manganese oxide and hexavalent chromium, the interference can be eliminated by measuring the content of both. Take 100 ml of sample in a 250 ml Erlenmeyer Add 1.0 ml of sodium arsenite solution (6.13) or thioacetamide solution (6.13) and mix. Add 15.0 ml phosphate buffer (6.11) and 5.0 ml DPD solution (6.12), immediately titrated with ammonium ferrous sulfate standard titration solution (6.9), the solution is titrated from pink to none the color is the end point and the interference of manganese oxide is measured. If hexavalent chromium is present, after 30 minutes, the color of the solution turns pink and continues to titrate hexavalent chromium.

The interference caused the solution to be titrated from pink to colorless as the end point. Record titration consumption solution volume V5, equivalent to dry manganese oxide and hexavalent chromium Disturb. If the water sample needs to be diluted, the manganese oxide and hexavalent chromium interference of the diluted sample should be determined.

9.3 Determination of total chlorine

In a 250 ml Erlenmeyer flask, add 15.0 ml phosphate buffer solution (6.11), 5.0 ml DPD solution (6.12) and sample.

(9.1), add 1 g of potassium iodide (6.4) and mix. After 2 min, titrate with ammonium ferrous sulfate standard titration solution (6.9) until colorless.

If a pink reproduction is observed within 2 min, the titration is continued until colorless as the end point, and the number of milliliters of the titration solution volume V4 is recorded.

For samples containing manganese oxide and hexavalent chromium, the interference can be eliminated by measuring the content. For the determination method, see 9.2.

10.1 Calculation of free chlorine

The mass concentration rho (calculated as Cl2) of free chlorine in the water sample is calculated according to the formula (3).

(Cl ) = 70.91

c VV

rho - × (3)

Where. c3-- ammonium ferrous sulfate standard titration concentration (in terms of Cl2), mmol/L;

V3--measurement (9.2) volume of the standard titration solution of ammonium ferrous sulfate, ml;

V5--correction of the volume of ammonium ferrous sulfate standard titration solution when interfering with manganese oxide and hexavalent chromium, ml, if manganese oxide and six are not present Chromium, V5=0 ml;

V0--sample volume, ml;

The relative molecular mass of 70.91--Cl2.

10.2 Calculation of total chlorine

The mass concentration rho of the total chlorine in the water sample (calculated as Cl2) is calculated according to the formula (4).

(Cl ) 70.91

c VV=

rho - × (4)

Where. V4--measurement (9.3) volume of the standard titration solution of ammonium ferrous sulfate, ml.

10.3 Results are expressed

When the measurement result is less than 10 mg/L, it is retained to two decimal places; when it is greater than or equal to 10 mg/L, three significant figures are retained.

11.1 Precision

Five laboratories tested uniform samples containing potassium iodate at concentrations of 1.006, 5.03, and 9.05 mg/L.

The relative standard deviations in the experimental room were. 7.6% to 9.6%, 1.0% to 3.8%, and 0.7% to 1.4%;

The relative standard deviations between laboratories were. 1.2%, 1.1%, 0.4%;

The repeatability limits were. 0.25 mg/L, 0.33 mg/L, 0.26 mg/L;

The reproducibility limits were 0.25 mg/L, 0.36 mg/L, and 0.27 mg/L, respectively.

11.2 Accuracy

Five laboratories used sodium hypochlorite to determine the three actual samples from tap water, medical wastewater and domestic sewage.

The spiked recovery rates were. 100% to 103%, 100% to 103%, and 98.1% to 106%;

The final recoveries of the spiked recovery were. 102% ± 2.2%, 99.0% ± 6.2%, and 102% ± 6.4%.