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The principle of testing is to convert 1-hydroxyethylidene-1 1-diphosphonic acid (HEDP) to ortho phosphorus. And then to measure phosphorous.

The aim of the test is to detect the content of phosphorus (total phosphorus) in water. This testing is divided into two parts. They are inorganic phosphorus and organic phosphorus. The inorganic phosphorus portion may be composed of orthophosphoric and polymeric phosphorus. The organophosphorus moiety consists solely of 1-hydroxyethylidene-1 1-diphosphonic acid.

The content of orthophosphate representing total phosphorus. The content of orthophosphate representing inorganic phosphorus. The difference between the two is the content of organophosphorus (i.e., HEDP) based on the phosphonate.

If several phosphonic acids coexist in the water, this method cannot be distinguished. What is measured is the total amount of various phosphonic acids.

1. Determination of positive phosphorus content (standard HG 5-1513-85).

1.1 Phosphomolybdenum blue spectrophotometry.

Orthophosphate and sodium molybdate form a phosphomolybdate heteropolyacid in an acidic medium. It is reduced to phosphorus molybdenum blue with stannous chloride. And then spectrophotometry was carried out at 660nm.

1.2 phosphorus vanadium molybdenum yellow spectrophotometry.

Orthophosphate and ammonium molybdate and ammonium metavanadate form a yellow phosphorus vanadium molybdenum heteropoly acid in an acidic medium. And then use the spectrophotometrically to measure at 420nm.

2. Determination of inorganic phosphorus content (standard: HG 5-1514-85).

2.1 Phosphomolybdenum blue spectrophotometry.

Under acidic boiling conditions. The polymeric phosphorus is gradually hydrolyzed to normal phosphorus. Then, a phosphorus molybdenum heteropoly acid is formed with sodium molybdate. After reduction with barium sulfate to form phosphorus molybdenum blue. Spectrophotometry was carried out at 660nm.

2.2 Phosphorus, vanadium, molybdenum and yellow spectrophotometry.

The hydrolyzed polymeric phosphorus is heated to positive phosphorus in a strongly acidic solution. The phosphorous is reacted with ammonium molybdate and ammonium metavanadate to form a yellow phosphorus vanadium molybdenum heteropolyacid. Spectrophotometry was carried out at 420nm.

3. Determination of total phosphorus content (standard: HG 5-1515-85).

3.1 Phosphomolybdenum blue spectrophotometry.

The organic phosphorus and polyphosphoric are decomposed into positive phosphorus by the strong oxidizing agent ammonium persulfate. Then, it reacts with sodium molybdate to form a phosphorus molybdenum heteropolyacid. After reduction with barium sulfate into phosphorus molybdenum blue. Spectrophotometry was carried out at 660nm.

3.2 Phosphorus, vanadium, molybdenum and yellow spectrophotometry.

The organic phosphorus and polyphosphoric are decomposed into positive phosphorus by the strong oxidizing agent ammonium persulfate. It is then reacted with ammonium molybdate and ammonium metavanadate to form a yellow phosphorus vanadium molybdenum heteropolyacid. Spectrophotometry was carried out at 420nm.

If it is known that there is no inorganic phosphorus in the water. The 1-hydroxyethylidene-1 1-diphosphonic acid can be oxidized by excess sulfuric acid in an acidic solution. In the presence of a ferrous standard solution. The excess sorghum sulfate is then back titrated in the presence of a ferrous target. The content of 1-hydroxyethylidene-1 1-diphosphonic acid HEDP in water can be determined from the number of milliliters of the ferrous standard solution consumed.

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