Determination of copper, zinc, cadmium and lead in a fish otolith certified reference material by isotope dilution inductively coupled plasma mass spectrometry using off-line solvent extraction

Copper, Zn, Cd and Pb concentrations in a fish otolith (ear stone) certified reference material (CRM) were determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). The material consists of almost pure calcium carbonate, and contained 39% calcium and less than 1 ppm of these heavy metals. An off-line solvent extraction was employed to separate the metals from the sample matrix. Contamination from reagents and from the extraction procedure was minimal and precise results were obtained for these four metals. The mean concentration (mg kg(-1) dry wt) and standard deviation (1 sigma) were 0.742 +/- 0.007 for Cu, 0.471 +/- 0.002 for Zn, 0.0028 +/- 0.0002 for Cd and 0.0234 +/- 0.0003 for Pb (n=5). An ICP-MS determination by external calibration after solvent extraction was used as a back-up method and the results obtained (Cu, 0.73; Zn, 0.43; Cd, 0.0028; Pb, 0.026; n=3 for each) were in good agreement with the ID-ICP-MS results. The present ID-ICP-MS results are used as reference values of the fish otolith CRM.