GB/T 19203-2003Determination of calcium, magnesium and sulphur content for compound fertilizer (English PDF)

3.1 General provisions

The preparation of reagents, water and solutions used in this Standard, in the

absence of specifications and preparation methods, it shall be in accordance

with the provisions of HG/T 2843-1997.

3.2 Laboratory sample preparation

Prepare the laboratory sample according to the provisions of GB/T 8571.

3.3 Preparation of sample solution

3.3.1 Reagents and materials

3.4.2.6 Ammonia-ammonium chloride buffer solution. pH ~ 10; prepare it

according to the method in 9.5.1 of HG/T 2843-1997;

3.4.2.7 Disodium edetate (EDTA) standard titration solution. c(EDTA) = 0.02

mol/L;

3.4.2.8 Malachite green indicator solution. 1 g/L;

3.4.2.9 Calcein - methyl thymol blue indicator (referred to as calcein indicator).

grind and well mix 0.10 g of calcein and 0.10 g of methyl thymol blue (or methyl

thymol blue), 0.03 g of thymol phenolphthalein, 5 g of potassium chloride; store

in grinding mouth bottle, it is ready for later use;

3.4.2.10 Acid chrome blue K-naphthol green B mixed indicator (referred to as

K-B indicator).

3.4.3 Apparatus

General laboratory instruments.

3.4.4 Analysis steps

3.4.4.1 Determination of total calcium content

3.4.4.1.1 Content determination

Accurately pipet a certain amount of sample solution (less than 15 mg, in Ca)

in an Erlenmeyer flask. Add 50 mL of water, 10 mL of starch solution, 8 mL of

triethanolamine solution, 1 mL of ethylenediamine, 1 drop of malachite green

indicator solution. Drop-add potassium hydroxide solution till it is colorless. And

add an excess of 10 mL. Add 0.1 g of hydroxylamine hydrochloride (each

reagent must be well shaken when it is added). Add 0.1 g ~ 0.3 g of calcium

yellow indicator. On a black background, immediately use disodium edetate

(EDTA) standard titration solution to titrate till green fluorescence disappears. It

shall be the end of titration when it appears in purple-red.

3.4.4.1.2 Blank test

Except that sample is not added, it must use reagents, dosage and analysis

steps which are identical with sample determination to carry out the parallel test.

3.4.5 Expression of analysis results

3.4.5.1 Total calcium (in Ca) content w1, expressed in mass fraction (%), shall

be calculated according to equation (1).

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