Determination of dissolved manganese(II) in coastal and estuarine waters by differential pulse cathodic stripping voltammetry

A method for the determination of dissolved manganese(II) in seawater utilizing cathodic stripping voltammetry on a rotating glassy carbon disk electrode is presented which is suitable for coastal and estuarine waters. The technique was accurate to within 2% in measuring manganese concentrations in CASS-3 Nearshore Seawater Reference Material, and manganese values determined on Narragansett Bay samples by this technique and by graphite furnace atomic absorption spectroscopy were in close agreement. Analytical conditions involve an oxidative deposition at a potential of +0.75 V and a pH of 8.5, followed by cathodic stripping in the differential pulse mode with a pulse modulation amplitude of 100 mV and a scan rate of 20 mV s−1. The sensitivity is 11 nA nM−1 min−1, and the detection limit 6 nM. This technique can be used to examine organic complexation of manganese, as it measures kinetically labile inorganic species, while Mn-organic chelates such as MnEDTA2− are inert. A preliminary examination of South San Francisco Bay water, however, found no evidence of organic complexation of manganese.