Rapid determination of toxic and rare-earth elements in teas by particle nebulization-ICPMS

Abstract

Toxic elements profiling of teas is vital in terms of both quality control as well as a means to generate a comprehensive database for human-health-risk assessment. Accordingly, in the present study, a rapid method using direct nebulization of tea particles for inductively coupled plasma (ICP) ionization and subsequent detection of toxic elements by mass spectrometry (MS) was developed. Dried and well grounded tea particles were stably dispersed in 0.5% polyethylene-imine and the particle slurries were analyzed by ICP-MS using aqueous standard calibration. Monitoring the nebulization, transportation, and ionization behaviors of particles of different sizes revealed that particles with a mean size of 1 μm provide values comparable with those of aqueous standards containing equivalent concentrations of the analyte. The excellent recoveries of the method (90–105%) were verified by analyzing two tea certified reference materials, and the detection limits ranged from 0.03 (for Tm) to 1.2 (for Cr) μg kg−1. Then, we performed screening analysis of five toxic elements (As, Cd, Cr, Hg, and Pb) and 16 rare-earth elements in 20 Pu’er teas, and the results revealed that the contents of all the toxic elements and heavy rare earth oxides were low level, where those of the light rare-earth oxides were high. Furthermore, the total rare-earth oxides content of 30% of the Pu’er teas exceeded the Chinese National limit.