Validation of Lead Determination in Materials of Animal and Plant Origin by Isotope Dilution Mass Spectrometry

Abstract

The method involves sample decomposition in a microwave oven with HNO₃ and H₂O₂ after addition of the spike of ²⁰⁴Pb isotope and measurement of (²⁰⁶Pb ²⁰⁷Pb ²⁰⁸Pb)/²⁰⁴Pb ratio. This measurement is more sensitive and more precise than the measurement of the ²⁰⁸Pb/²⁰⁴Pb ratio. The optimum sample mass and the spike amount for a wide working range were chosen by computer simulation of uncertainty. The method is robust, and the results are not influenced by small changes in the apparatus setting (i.e., rf power, Ar nebulizer flow, ion lens voltage). The accuracy of the method was verified by analysis of several CRM and by analysis of an in-house prepared primary solution of Pb. The detection limit is 10 ng per gram of Pb and the reproducibility of the method is 4 ng per gram of Pb. The interferences of ²⁰⁴Hg and ¹⁸⁶W¹⁸O ions were found to be negligible with respect to the content of mercury and tungsten in animal and plant samples.