Polarographic determination of orthophosphate in seawater

In the system HCl-Sb (Ⅲ)-ammonium molybdatc-acetone-butanone, PO₄^3-, Sb (Ⅲ) and Mo (VI) form ternary heteropoly acid. This ternary heteropoly acid anion is adsorbed on the dropping mercury electrode and reduced quickly into heteropoly blue. The process of electrochemical reaction will produce a sensitive polarographic wave with peak potential -0.42V (vs S.C.E.). The detection limit is 6×10^-8 mol/l. Variable coefficients are 10% and 3% for 0.1 μmol/l and 1 μmol/l respectively.
This method is sensitive, accurate and extremely rapid for analysis of seawater.