The Shipboard Determination of Iron(III) in Seawater Using Continuous Flow Analysis with Colorimetric Detection

Laboratory experiments were performed to adapt a catalytic colorimetric method to continuous flow analysis for the shipboard determination of iron(III) in seawater. System parameters such as reagent concentrations, reaction temperature, flow rate, reaction coil length, pH and buffer grade were optimized to increase sensitivity and decrease background absorbance. The method is based on the catalytic effect of iron(III) on the oxidation of N, N-dimethyl-p-phenylenediamine by hydrogen peroxide, and has an optimal detection limit of 0.2 nM. Preliminary shipboard testing of the system was conducted to determine if this method would be tactically useful when applied to a near real time chemical mapping strategy. A mesoscale fertilization experiment, IronEx-1, was performed in the equatorial Pacific in October, 1993. Data were collected over a 24 hr. period following iron enrichment. Iron concentrations measured by this method compared well with those determined by an independent, semicontinuous chemiluminescence method using samples collected at the same time.