Accurate determination of lead in Chinese herbs using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS)

A method for the determination of Pb in Chinese herbs based on “approximate matching” isotope dilution inductively coupled plasma mass spectrometry was developed. The method was validated using NIST SRM 1547 (Peach Leaves). Satisfactory analytical figures of merit were achieved, including good sample recovery (∼99%) and low relative expanded uncertainty (less than ±2%). The validated method was applied to the analysis of a herbal sample for the international comparison CCQM-P97. Measurement uncertainty was evaluated according to three approaches, namely Kragten’s spreadsheet approach, GUM Workbench and Monte Carlo method (MCM). A practical way was established for the evaluation of measurement uncertainty based on the propagation of distributions using MCM. The validated method was also employed for the provision of SI-traceable mass fraction of Pb in an in-house herbal reference material and the assignment of a reference value to a proficiency testing programme.