Determination of dissolved inorganic phosphate by an extraction procedure high-sensitivity method

7 Determination of dissolved inorganic phosphate by an extraction procedure (high-sensitivity method) 

The detection limit of the main procedure (Section 10.2.5) for the determination of dissolved phosphate in seawater is about 0.01-0.02/tmol/L, a sensitivity that is satisfactory for most marine investigations. In special biological studies, however, the determination of phosphate below this level is sometimes necessary. Increased sensitivity can be obtained by solvent extraction of the phosphomolybdic acid, followed by reduction in the organic phase or by extraction of the already reduced blue complex. Stephens (1963) combined the single solution method by Murphy and Riley (1962) with solvent extraction. This method has been adopted by Strickland and Parsons (1968). 

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