DETERMINATION OF CADMIUM AND BISMUTH IN HIGH-PURITY ZINC METAL BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY WITH ONLINE MATRIX SEPARATION

Traces of cadmium and bismuth in high-purity zinc metal were determine d by inductively coupled plasma mass spectrometry (ICP-MS) in combinat ion with flow injection (FI) on-line matrix separation (FI-ICP-MS). Th e anion-exchange separation method of the potassium iodide (KI) system was applied to the separation of the analytes from the matrix zinc. T he analytes, cadmium and bismuth, were adsorbed on the anion-exchange (BIO . RAD AG1-X8) mini-column (1.0 mm i.d. x 100 mm bed length), whil e the matrix zinc can be completely removed from the anion-exchange re sin. The analytes were eluted by 2 mol/l HNO3 and directly introduced into the ICP-MS. The detection limits (D.L.) obtained by using a singl e injection (350 mu l) were 0.81 and 0.075 ng g(-1) for cadmium and bi smuth, respectively. In the case of multi-injection concentration onto the anion-exchange mini-column (five injections 350 mu l each), the d etection limits could be improved to 0.16 and 0.014 ng g(-1) for cadmi um and bismuth, respectively. The reproducibilities of the single inje ction and the multi-injection method were satisfactory with a relative standard deviation of less than 5% (at the 10 and 1 ng ml(-1) level f or the single injection and the multi-injection method, respectively). The method was successfully applied to the determination of trace imp urities in four samples of high-purity zinc metal (7 nines grade) and three standard reference materials of high-purity unalloyed zinc sampl es (from NIST).