Direct determination of molybdenum in seawater by adsorption cathodic stripping square-wave voltammetry

A reliable and very sensitive procedure for the determination of trace leve ls of molybdenum in seawater is proposed. The complex of molybdenum with 8- hydroxyquinoline (Oxine) is analyzed by cathodic stripping square-wave volt ammetry based on the adsorption collection onto a hanging mercury drop elec trode (HMDE). This procedure of molybdenum determination was found to be mo re favorable than differential pulse cathodic stripping voltammetry because of inherently faster scan rate and much better linearity obtained through the one-peak (instead of one-of-two peaks) calibration. The variation of po larographic peak and peak current with a pH, adsorption time, adsorption po tential, and some instrumental parameters such as scan rate and pulse heigh t were optimized. The alteration of polarographic wave and its likely mecha nism are also discussed. The relationship between peak current and molybden um concentration is linear up to 150 mu g l(-1). Under the optimal analytic al conditions, the determination limit of 0.5 mu g l(-1) Mo was reached aft er 60 s of the stirred collection. The estimated detection limit is better than 0.1 mu g l(-1) of Mo. The applicability of this method to analysis of seawater was assessed by the determination of molybdenum in two certified r eference seawater samples (CASS-2 and NASS-2) and the comparison of the ana lytical results for real seawater samples (study on a vertical distribution of Mo in the seawater column) with the results obtained by Zeeman-correcte d electrothermal atomization atomic absorption spectrometry (Zeeman ETAAS). A good agreement between two used methods of molybdenum determination was obtained. (C) 2000 Elsevier Science B.V. All rights reserved.