Direct determination of trace metals in sea-water using electrothermal vaporization inductively coupled plasma mass spectrometry

Electrothermal vaporization (ETV) was used as an alternative method of sample introduction for inductively coupled plasma-mass spectrometry (ICP-MS). The capacity of the graphite furnace for in-situ matrix separation was coupled with the high-sensitivity and multi-element detection capability of ICP-MS. This ETV-ICP-MS method was applied to the determination of trace metals in sea-water samples. Five metals were selected, cobalt, copper, manganese, nickel and vanadium. Matrix interferences were eliminated by the use of ETV and the use of nitric acid as a chemical modifier which facilitated the removal of chloride during the sample drying stage. Optimization of the ETV heating programme resulted in effective separation of residual matrix and analyte species, thus reducing ionization suppression and space charge effects in the ICP-MS. Detection limits ranged from 0.003 ug per litre for vanadium to 0.14 ug per litre for copper. The method was validated by use of 2 certified sea water reference materials (NASS-3 and CASS-4). Calibration standards were prepared using a sea water matrix stripped of trace metals by ion exchange. Calibration graphs were linear and allowed direct determination of selected analytes without resorting to the standard additions method.