SHIPBOARD FLOW-INJECTION METHOD FOR THE DETERMINATION OF MANGANESE IN SEA-WATER USING IN-VALVE PRECONCENTRATION AND CATALYTIC SPECTROPHOTOMETRIC DETECTION

A flow injection method for the determination of manganese at trace level concentrations in sea-water is proposed. The in-valve ion-exchange microcolumn for preconcentration was directly coupled to the spectrophotometer. The spectrophotometric detection was based on the catalytic effect of Mn(II) on the oxidation of N,N-diethylaniline by potassium periodate in a neutral medium. Variation of the preconcentration time from 10 s to 10 min allowed the determination of manganese in the concentration range 20-mu-g-1-10 ng l-1. A sampling frequency of up to 15 h-1 and a relative standard deviation of 5-8% were achieved. The proposed method was successfully applied to the direct shipboard measurement of the manganese content in deep sea-water samples for the purpose of indicating the presence of active hydrothermal vents on the sea floor.