Abstract

In this paper we describe a hydride generation system for measuring the inorganic and methylated species of three metalloids, Ge, Sb and As, in marine and freshwater samples. The system utilises the principles of both flow injection and batch hydride generation and couples it to an automated cryogenic trapping unit with detection by ICP-MS. The Teflon cryogenic trap was packed with 10 cm of SE-30 5% Chromosorb W-HP 80–100 mesh and wound with 1.2 m of resistance wire. A motorised cryofocusing unit was designed and built to lower and raise the hydride trap into and out of a liquid nitrogen dewar and to control the heating of the hydride trap. The compromise conditions for hydride generation and cryogenic trapping of inorganic and methylated species were final solution concentrations of 0.06 M hydrochloric acid, 0.5% w/v sodium tetrahydroborate and 0.5% w/v cysteine. For measurement of As^III and Sb^III cysteine was omitted. Samples were purged and trapped with helium at a flow rate of 80 ml min⁻¹. One run took 8.75 min for a 1 ml sample. Detection limits were 1-5 pM for Ge species, 0.001–0.004 nM for Sb species and 0.002–0.069 nM for As species. The analytical precision for inorganic and methylated species was 2–8% for all but two of the species (TMSb, 20% and DMSb, 11%) at concentrations typically found in the environment. Results for a range of natural waters are presented to illustrate the use of the system.