10.2.5 Determination of dissolved inorganic phosphate
10.2.5.1 Principle of the method
All methods for the determination of inorganic phosphate in seawater are based on the reaction of the ions with an acidified molybdate reagent to yield a phosphomolybdate heteropoly acid, which is then reduced to a highly coloured blue compound. In early work, tin(II) chloride was used as the reductant in flow-analysis (Hager et al,1968).However, this reductant has serveral disadvantages, including the appreciable temperature dependence of the reduction rate and the pronounced salt error.