Sulphides and hydrogen monosulphide

Sulphides and hydrogen monosulphide at concentrations 0.05 mg 1 are determined photometrically with iV, iV-dimethyl-p-phenylenediamine. A sensitive and selective determination is based on the production of Methylene Blue during the reaction of hydrogen monosulphide with the above reagent in the presence of Fe  

For the determination of higher amounts of hydrogen monosulphide (0.5-20 mg 1 ) and sulphides a iodometric method can be used. In this case sulphides and hydrogen monosulphide are separated in the form of a mixture of insoluble CdS and Cd(OH)2. The precipitate is separated, and known amounts of iodine and HCl are added. Iodine required for oxidation is determined from the difference between the added and remaining quantity of iodine, by titration with thiosulphate [13, 14]. 

For the determination of sulphides thin-layer chromatography [55, 56] is used, as well as spectrophotometry in the IR region [57], AAS [58], and a sulphide ion selective electrode [59-61]. 

The most important forms of phosphorus are inorganic orthophosphates which are determined photometrically with molybdenum. Orthophosphates react with ammonium molybdate in the presence of sulphuric acid and antimony ions to form heteropolyacids — phosphomolybdic acid. By reduction with ascorbic acid the yellow complex of phosphomolybdic acid changes into a solution of Phosphomolybdic Blue which can be determined photometrically  

Absorbance is measured at 690 nm (red filter). The method is used for the determination of soluble inorganic orthophosphates at concentrations 0.05 mg 1 . For low concentrations ( 0.005 mg 1 ) the extraction of Phosphomolybdic Blue into butyl alcohol can be used [14, 16, 62]. 

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