Ascorbic acid was first used in the analysis of seawater by Greenfield and Kalber (1954), but present method essentially follow the procedure by Murphy and Riley (1962), in which trivalent antimony ions are component of a single solution reagent. This reagent reacts rapidly with phosphate ions to yield a bluish complex containing antimony in a 1:1 atomic ratio to phosphorus, The method described here is a modification of the Murphy and Riley procedure as given by Koroleff in the first edition or this book. Two solutions are used instead of a single reagent : the first contains sulphuric acid, ammonium molybdate and antimony ions