Study of enrichment difference of 64 elements among white tea subtypes and tea leaves of different maturity using inductively coupled plasma mass spectrometry.

A microwave digestion-inductively coupled plasma mass spectrometry (ICP-MS)-based analytical method for 64 elements in white tea was developed. The determination coefficient R2 were ranged from 0.9970 to 1.0000 in 3 orders of magnitude for the 64 detected elements, and the limits of detection (LODs) of the method were from 0.0004 to 35.906 ng/mL. The stability of the method was monitored by quality control samples (QCs) and the accuracy was validated by certified reference material. Application of this method in 3 white tea subtypes showed that most of 54 elements that above LODs (Al, Pb, Cd, Hg, As, rare earth elements, and etc.) displaying gradually increasing trend in subtypes of Baihaoyinzhen, Baimudan, and Shoumei which are manufactured from tea leaves of increasing maturity, while few elements (Zn, P and Ni) decreased. Then, a further application of this method in fresh samples of the bud and the 1st, 2nd, 3rd, 4th, and 5th leaf confirmed that more mature tea leaf has higher enrichment efficiency for most elements. In conclusion, a comprehensive microwave digestion-ICP-MS-based analytical method was established and applied in the content measurements of 64 elements in 3 white tea subtypes and fresh tea leaves of different maturity, and it demonstrated that more mature tea leaf has higher enrichment efficiency for most elements.