Speciation of iron in seawater of Jiaozhou Bay in Qingdao was investigated by cathodic stripping voltammetry method which take advantage of ligand competition of an added electroactive ligand

1-nitroso-2-naphthol（NN）

with the natural organic complexing mater to evaluate whether iron is organically complexed. The measurements indicate that iron occurs 99% complexed by organic comlpexing ligands in seawater of the Jiaozhou Bay in Qingdao. The concentration of natural organic ligands was 47. 6nmol· L

-1

The conditional stability constant logK

FeL

is 21. 09.