Chemical forms of zinc in sea water

Recent experimental evidence concerning the chemical forms of zinc occurring in sea water is reviewed in order to aid in the systematic understanding of zinc geochemistry in the marine environment. The review indicates the necessity of systematizing the results obtained by different methods for the determination of zinc in sea water with respect to the chemical nature of the zinc fractions measured. Analytical procedures for the zinc determinations in sea water by spectrophotometry with dithizone extraction and anodic stripping voltammetry with composite mercury graphite electrodes are described. By using these methods, various pre-treatment tests were carried out to relate the results of different modes of measurements to the chemical forms of zinc involved. The comparisons of the results of these tests lead to an estimation of the occurrence of the following categories of chemical forms of zinc in sea water: (1) ionic plus labile form, (2) inorganic complexes and colloids as well as weak organic complexes and (3) occuled fraction in large organic molecules and/or organic colloids. Capabilities of different analytical procedures for differentiating one category from another are discussed.