Determination of zinc in plant samples by isotope dilution inductively coupled plasma mass spectrometry

Determination of zinc involved spiking with 68Zn enriched solution, digestion by HNO3+H2O2 in microwave decomposition unit, off-line separation of zinc on Chelex-100 column and measurement of (64Zn+66Zn)/68Zn isotope ratio on ICP-MS spectrometer with a quadrupole mass filter. After optimization of standard operation procedure (details are given) the method was validated. LOD was found to be 0.3 μg g−1 for the procedure without zinc separation and 3.6 μg g−1 for the procedure involving zinc separation, respectively. The accuracy of results was proved by analyses of several CRM and a primary solution of zinc, the concentration of which was verified by gravimetry and complexometric titration. Barium is the only element causing serious interferences and it must be removed from samples. The uncertainty budget is given together with the scheme of combined uncertainty calculation. The main uncertainty components are contamination during zinc separation and uncertainty of isotopic composition of natural zinc.