Dissolved organic iodine in marine waters: Determination, occurrence and analytical implications

An analytical scheme for the determination of dissolved organic I, DOI, in marine waters has been designed. The concentration of total I is determined as IO3− or I− after DOI has been oxidized to IO3− quantitatively by UV irradiation and all the inorganic I formed and present initially in the sample have been converted to the appropriate form for detection. The concentration of DOI is estimated as (total I−TII) where TII, or total inorganic I, represents the sum of the directly and independently determined concentrations of IO3− and I−. The precision for the determination of total I and DOI are ±0.008 and ±0.02 μM, respectively. DOI was found ubiquitously in coastal waters. It constituted up to 40% of total I and is therefore a significant, and heretofore largely neglected, pool of dissolved I. The concentration of DOI decreased with depth and increased shoreward in the surface waters. The concentration of DOI has probably been underestimated in previously reported analytical schemes. The contribution of DOI to dissolved I may be safely neglected probably only in the deep oceans.