COMBINED GENERATOR/SEPARATOR FOR CONTINUOUS HYDRIDE GENERATION - APPLICATION TO ONLINE PRE-REDUCTION OF ARSENIC(V) AND DETERMINATION OF ARSENIC IN WATER BY ATOMIC EMISSION-SPECTROMETRY

A continuous hydride generator is described which incorporates a combined generator/separator. The low acid concentrations necessary in the tetrahydroborate(III)-L-cysteine mediated determination of most hydride-forming elements require that the gas is purged from solution. As the hydride transfer reaction is so rapid, this allows both the hydride-forming reaction and the stripping reaction to take place in the same vessel. The system has been further modified to allow on-line pre-reduction of arsenic(v) to arsenic(III) by L-cysteine. Detection limits for arsenic, germanium and selenium are 4, 0.3 and 8 ng ml-1, respectively, at a sample flow rate of 15 ml min-1. Application of the system to the determination of arsenic in water is described. Concentrations of arsenic in several Ontario waters were found to be in the range 7-600 ng ml-1. Interferences from nickel and palladium, two of the most strongly interfering elements in the continuous hydride generation process, are diminished to a greater extent with the system described here than with the conventional high acid continuous system.