An on-line flow injection sample pretreatment procedure for matrix elimination and preconcentration in the determination of trace metals in seawater is described. The Method involves chelation of the trace metals onto an imminodiacetate-based resin column and elution with 2M nitric acid. Preconcentration factors between 4 and 155-fold were obtained for sample volumes ranging from 2ml to 17ml for several 1st row transition elements.
An alternative Electrothermal Vaporisation pretreatment method removes the predominant Sodium Chloride matrix prior to determination by ICP-MS allowing for interference free analysis of trace metals in seawater. Much of the seawater matrix can be removed by the use of controlled ashing in the Electrothermal Vaporiser (ETV) prior to sample analysis by ICP-MS. Ashing studies have shown that for the transition elements, ashing at between 1000 and 1150°C with addition of 5% HNO3 will give up to 100% spiked recovery for analyte samples, particularly if a slower vaporisation temperature ramp (1 sec) is applied. Optimum ashing times of around 30s have been established.
The merits of both techniques are discussed with respect to direct dilution nebulisation approaches with ICP-MS analysis Detection limits were found to be equivalent to those found with direct nebulisation of the equivalent concentrations of analytes in aqueous solutions.