Phospho-organic complexes

Standard methods for phosphates, polyphosphates, and organic phosphates in environmental samples are predominantly nonchromatographic methods, which are based upon the molybdenum blue method. Within this colorimetric method ammonium molybdate and antimony potassium tartrate react under acidic conditions with dilute solution of phosphorous to form an antimony-phospho-molybdate complex which is then reduced to an intensely blue-colored complex by ascorbic acid. U.S. EPA Methods 365.1 to 365.4 are based upon this chemistry. 

All methods for phosphate in sea water rely on the formation of a phospho-molybdate complex and its subsequent reduction to highly coloured blue compounds. Methods using stannous chloride as a reductant at room temperature have been fevoured as they arc most sensitive and give less interference from easily hydrolysable organic compounds than do other techniques. There are complexities in these methods due to interference from arsenic and to concealed blanks arising from the reduction of molybdate in sea water in the absence of phosphate. An excellent program of comparative tests has been described by Jones and Spencer (7. Marine Bid. Assoc. U.K., 43 251, 1963). 

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