Jinchun Yuan

Determination of iron in seawater by flow injection analysis using in-line preconcentration and spectrophotometric detection

A highly sensitive flow injection analysis (FIA) method for determining the concentration of iron in seawater has been developed. The technique is a modification of the catalytic batch method previously reported by Hirayama and Unohara. By optimising the chemistry for FIA and incorporating in-line preconcentration of the iron from seawater onto a column of resin-immobilised 8-hydroxyquinoline, the detection limit of the method has been reduced to 0.025 nM. The typical precision of the method for a 0.35 nM Fe sample is 2.5% (n = 6). The method has been used at sea in its preconcentration mode to determine iron in open ocean water samples from the equatorial Pacific and the North Atlantic. It has also been used in a direct injection mode for hydrothermal plume samples from around Loihi Seamount in the Central Pacific.

Hydrogen peroxide in deep waters of the North Pacific Ocean

[1] Hydrogen peroxide is a reactive oxygen intermediate that can play a role in a variety of redox cycles. In the ocean, it is generally considered to be dominantly photo-produced with negligible concentrations in deep waters. We have utilized a highly sensitive analytical method to investigate hydrogen peroxide in deep waters of the North Pacific Ocean. We present evidence that hydrogen peroxide exists in low nanomolar concentrations in these deep waters with an apparent minimum in the depth range of the oxygen minimum. A consideration of possible mechanisms and rates suggests both a short (∼12 day) residence time as well as a biological origin for this deep hydrogen peroxide. Hydrogen peroxide is probably of minor importance to metal cycling in the deep ocean except in low oxygen environments.