Determination of Trace Amounts of Bismuth in Steel by ICP-MS Through a Cascade-preconcentration and Separation Method

Determination of trace amounts (similar to 0.05 mu g) of bismuth in steel by inductively coupled plasma mass spectrometry (ICP-MS) has been carried out by a cascade-preconcentration and separation method that combines the one-drop solvent concentration method and solid-phase extraction method. The bismuth(III) ion from acid decomposition of the steel sample formed a complex with iodine, and this subsequently formed an ion pair with tetrabutylammonium (TBA). This ion pair was almost completely adsorbed by passage through a solid-phase packed column. The ion pair was eluted with ethyl acetate, and a small volume of dimethyl sulfoxide (DMSO) was added to the resulting solution; successful pre-concentration of the iodobismuthate complex/TBA ion pair into the DMSO phase was accomplished by removing the ethyl acetate using a compact evaporator in a water bath (40 degrees C). The sample was diluted with an internal standard (thallium) solution and an acidic solution and was then tested by ICP-MS. The calibration curve for the proposed method showed good linearity (r(2) = 0.9997) in the 0.05-10 mu g range. A recovery test was performed, in which 0.05 mu g and 2.5 mu g of bismuth was spiked into an acidic decomposition solution of pure iron (JSS 003-6), and the recovery was 98% for both solutions, and the relative standard deviations (n = 5) were 8.8% and 1.2%, respectively. Good results were obtained applying the method to analysis of CRMs.