GB/T 5750.11-2006Standard examination methods for drinking water -- Disinfectants parameters (English PDF)

1.1 N,N-Diethyl-p-phenylenediamine (DPD) spectrophotometry

1.1.1 Scope

This standard specifies the use of N,N-diethyl-p-phenylenediamine (DPD)

spectrophotometric method to determine free residual chlorine in drinking water

and its source water.

This method is applicable to the determination of free residual chlorine and

combined residual chlorine in various forms in drinking water and its source

water after chlorination and disinfection.

The minimum detection mass of this method is 0.1 µg. If a 10 mL water sample

is taken for the determination, the minimum detection mass concentration is

0.01 mg/L.

High concentrations of monochloramine interfere with the determination of free

residual chlorine, arsenite or thioacetamide can be used to control the reaction

to remove interference. Manganese oxide interference can be eliminated from

making the water sample blank. Chromate interference can be eliminated with

thioacetamide.

1.1.2 Principle

DPD reacts rapidly with free chlorine in water to produce red color. Under the

catalysis of iodide, monochloramine also reacts with DPD to develop color.

When iodide is added prior to the addition of the DPD reagent, a portion of the

trichloramine is developed with the free residual chlorine, and the concentration

of trichloramine can be determined by changing the order of addition of the shift

reagent. This method can use potassium permanganate solution to prepare a

permanent standard series.

1.1.3 Reagents

1.1.3.1 Potassium iodide crystals.

1.1.3.2 Potassium iodide solution (5 g/L). WEIGH 0.50 g of potassium iodide

(Kl), DISSOLVE it in fresh boiled cold purified water, DILUTE it to 100 mL.

permanganate in the standard solution is similar to the DPD and the red color

of the indicated residual chlorine.

1.1.3.9 Chlorine standard use solution [p(Cl2) = 1 µg/mL]. PIPETTE 10.0 mL of

chlorine standard stock solution (1.1.3.8), ADD pure water to dilute it to 100 mL.

MIX it uniformly, TAKE 1.00 mL and DILUTE it to 100 mL.

1.1.4 Instruments

1.1.4.1 Spectrophotometer.

1.1.4.2 Stoppered colorimetric tube, 10 mL.

1.1.5 Analytical procedure

1.1.5.1 Standard curve drawing. PIPETTE 0, 0.1, 0.5, 2.0, 4.0, 8.0 mL of

chlorine standard use solution (1.1.3.9) into six 10 mL stoppered colorimetric

tubes, USE water requiring no chlorine (1.1.3.7) to dilute it to the mark.

Respectively ADD 0.5 mL of phosphate buffer solution (1.3.3.3) and 0.5 mL of

DPD solution (1.1.3.4), MIX it uniformly. DETERMINE the absorbance at a

wavelength of 515 nm in a 1 cm cuvette with pure water as a reference. DRAW

a standard curve.

1.1.5.2 PIPETTE 10 mL of water sample into a 10 mL colorimetric tube, ADD

0.5 mL phosphate buffer solution (1.1.3.3), 0.5 mL of DPD solution (1.1.3.4),

MIX it uniformly; immediately DETERMINE the absorbance at a wavelength of

1.1.5.3 CONTINUE adding a small crystal of iodinated crystal (about 0.1 mg) to

the above test tube. After mixing it uniformly, MEASURE the absorbance,

RECORD the reading as B.

Note. If the content of dichloramine in the sample is too high, it may add 0.1 mL

of freshly prepared potassium iodide solution (1 g/L).

1.1.5.4 Then ADD potassium iodide crystal (about 0.1 g) to the above tube, MIX

it uniformly. After 2 min, MEASURE the absorbance and RECORD the reading

as C.

1.1.5.5 Take another two 10 mL colorimetric tubes, TAKE 10 mL of water sample

in one of the colorimetric tubes, then ADD a small amount of potassium iodide

crystal (about 0.1 mg), MIX it uniformly; ADD 0.5 mL of buffer solution (1.1.3.3)

and 0.5 mL of DPD solution (1.1.3.4) into the second colorimetric tube, POUR

4.1.1 Scope

This standard specifies the use of N,N-diethyl-p-phenylenediamine (DPD)-

ammonium ferrous sulfate titration method for the determination of chlorine

dioxide in drinking water.

This method applies to the determination of chlorine dioxide in drinking water.

The method requires that the total available chlorine (Cl2) of the water sample

be no higher than 5 mg/L. Once above this value, the sample must be diluted.

The determination scope of this method is 0.025 mg/L ~ 9.5 mg/L, the minimum

detection concentration is 0.025 mg/L (ClO2).

Oxidized manganese and chromate can make DPD produce color, resulting in

high measurement results, it may add sodium arsenite or thioacetamide to the

water sample to correct it; since the entering of titration solution into iron ion

can activate chlorite and interfere with the titration end, it can add

ethylenediaminetetraacetic acid disodium to inhibit it.

4.1.2 Principle

Glycine converts free chlorine in water to glycine chloride without disturbing the

determination of chlorine dioxide. Chlorine dioxide in water reacts with DPD in

red. It is titrated with ammonium ferrous sulfate standard solution. The addition

of phosphate buffer salt will keep the water sample neutral. Under this condition,

chlorine dioxide gets only 1 mol of electrons and is reduced to ClO2-. The

amount of ammonium ferrous sulfate in the water sample can be used to

calculate the mass concentration of the oxygen dioxide.

4.1.3 Reagents

4.1.3.1 Potassium dichromate standard solution [c(1/6K2Cr2O7) = 0.1000 mol/L].

WEIGH 4.904 g of the dried reference potassium dichromate, DISSOLVE it in

distilled water, MAKE its volume reach to 1000 mL, STORE it ground glass

bottles.

4.1.3.2 Bismuth diphenylamine sulfonate solution (1 g/L). WEIGH 0.1 g of

diphenylamine sulfonic acid hydrazine [(C6H5NHC6H4-SO3)2Ba] in 100 mL of

distilled water.

4.1.3.3 Ammonium ferrous sulfate standard solution {c[(NH4)2Fe(SO4)2] =

0.003000 mol/L}. WEIGH 1.176 g of ammonium ferrous sulfate

[Fe(NH4)2(SO4)2-6H2O] into the distilled water containing 1 mL of sulfuric acid

solution (1 + 3), USE the newly boiling and cooled distilled water to dilute it to

13.49 x 5 - The actual mass of chlorine dioxide in milligrams equivalent to

1.00 mL of ammonium ferrous sulfate {c[(NH4)2Fe(SO4)2] = 1.000 mol/L.

4.2 Iodometric method

4.2.1 Scope

This standard specifies the use of iodometric method for the determination of

chlorine dioxide in pure chlorine dioxide aqueous solution.

This method is applicable to the determination of chlorine dioxide in pure

chlorine dioxide solution.

The minimum detection mass of this method is 10 µg (by ClO2). If 500 mL of

aqueous solution is used, the minimum detection mass concentration is 20 µg/L

(by ClO2). Temperature and strong-light can affect the stability of the solution,

so the chlorine dioxide stock solution shall be protected from light, sealed, and

stored refrigerated. In order to minimize the loss of chlorine dioxide, the

preparation and calibration procedures are required to be performed at room

temperature not exceeding 20 °C and in non-direct light.

4.2.2 Principle

Sodium chlorite solution (NaClO2) reacts with dilute sulfuric acid to produce

chlorine dioxide. Impurities such as chlorine are removed...

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