Sensitive determination of three arsenic species in water by ion exclusion chromatography-hydride generation-inductively coupled plasma mass spectrometry

A sensitive and robust method for the speciation of arsenic in water was developed. Arsenic(V), arsenic(III) and monomethylarsonic acid (MMA) were separated by ion exclusion chromatography on a sulphonated polystyrene resin using dilute trifluoroacetic acid at pH 2.1 as the mobile phase, and then quantified by hydride generation inductively coupled plasma mass spectrometry. Use of hydride generation as the sample introduction technique improved sensitivity and eliminated interference from chloride ions. The detection limits, using an injected volume of 50 ul, were 1.1 pg per ml for arsenic(V) and 0.5 pg per ml for both arsenic(III) and monomethylarsonic acid; these detection limits were more than 20 times lower than reported values, probably due to the use of a high purity acid as the mobile phase. The analysis time was approximately 18 minutes, but was reduced to 9 minutes by using a column-switching method. The method was applied to the analysis of 3 reference riverine water samples (JAC0031, SLRS-1 and SLRS-3), 1 reference estuarine sample (SLEW-2, salinity 11.6 per cent) and 1 reference seawater sample (CASS-3, salinity 30.2 per cent). The sum of the arsenic(V) and MMA concentrations for CASS-3 and SLEW-2 were in good agreement with the certified values, but the results for SLRS-1 and SLRS-3 showed large deviations from the certified data. The principal disadvantage of the method was its failure to elute dimethylarsinic acid.