DETERMINATION OF GERMANIUM BY ISOTOPE-DILUTION HYDRIDE GENERATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

Inorganic germanium in aqueous solution is determined by a combination of isotope dilution, hydride generation, and inductively-coupled plas ma mass spectrometry (ID-HG-ICP-MS). Samples (5-20 ml) are spiked with an enriched stable isotope (Ge-70). Germanic acid is reduced by sodiu m borohydride to germane (GeH4), stripped in He gas and collected on a liquid nitrogen trap. The hydrides are subsequently evaporated from t he cold trap and introduced into the ICP torch. The ion counts at m/z= 70 and 74 are monitored during the transient hydride peak. Absolute de tection limits are about 400 fg. The method has an overall precision o f better than 2% RSD and a dynamic range of two orders of magnitude. T he method was applied to seawater samples and rock standards. Results are in excellent agreement with those determined previously by other m ethods. As an alternative method to isotope dilution, single ion monit oring (m/z=74; SIM-HG-ICP-MS) with trimethylgermanium added as an inte rnal standard can be used to improve absolute detection limits (200 fg ) while still maintaining a precision of +/-2 to 4%.