Determination of Silicon Content in White Tea via inductively Coupled Plasma Atomic Emission Spectrometry

Objective A method of inductively coupled plasma atomic emission spectrometry (ICP-AES) was developed to determine the silicon content in white tea.

Method White tea was ground, passed through a 5.0 μm-mesh sieve, dried in an oven at 80°C for 4 h, cooled in a desiccator, sample weighed, and placed in a silver crucible to be carbonized on an electric furnace and then heated to 650°C in a muffle furnace till constant weight. The ash was treated by alkali fusion and followed by hydrochloric acid extraction prior to an ICP-AES determination for silicon.

Result The assay produced a linear function with a correlation coefficient greater than 0.999, a detection limit of 0.002 mg·L⁻¹, a relative standard deviation of 2.41%, and a recovery rate of 97.2-103.2% on the silicon standards. Different types of aged white teas including 1-, 3-, 7-, and 10-year-old Baimudan and Shoumei, and 1- and 3-year-old wild Baimudan white tea were tested in a trial run. Baimudan white tea consistently had a higher silicon content than Shoumei of a same age, with wild Baimudan white tea not included.

Conclusion The newly established silicon assay on white teas by ICP-AES was precise, accurate, and repeatable. Significant differences in the content were clearly shown among the various white teas. Thus, the detection result could serve as an indicator for quality improvement on the tea.