Precise determination of dissolved platinum in seawater of the Japan Sea, Sea of Okhotsk and western North Pacific Ocean

Platinum is among the least abundant elements in the earth's crust and is now widely used in various products such as catalytic converters in automobiles and anticancer drugs. Consequently, the concentration of Pt in urban aquatic environments is increasing. However, little is known about the distributions and geochemical cycles of Pt in the ocean owing to its low concentrations in seawater (< 0.2 pmol/L). In this study, we report an improved analytical method for determining sub-picomolar levels of Pt in seawater, and reveal the distributions of Pt in the Japan Sea, Sea of Okhotsk, and western North Pacific Ocean.For determining sub-picomolar levels of Pt in seawater, we used isotope-dilution ICP-MS (Inductively Coupled Plasma Mass Spectrometry) after column preconcentration with an anion exchange resin. This method facilitated highly accurate analysis of Pt in seawater using small sample volumes (~ 1 L). The detection limit and procedural blank value for this method were 0.015 and approximately 0.01 pmol/L, respectively. We obtained conservative vertical distributions, with nearly constant Pt concentrations between 0.19 and 0.25 pmol/L in the Japan Sea, Sea of Okhotsk, and western North Pacific Ocean. Judging from the constant dissolved Pt profiles, little anthropogenic influence of Pt is apparent in the open oceans at the present time.