Multielement Determination and Speciation of Major-to-Trace Elements in Black Tea Leaves by ICP-AES and ICP-MS with the Aid of Size Exclusion Chromatography

摘要

A multielement determination of major-to-trace elements in black tea leaves and their tea infusions was carried out by ICP-AES (inductively coupled plasma atomic emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). Tea infusions were prepared as usual tea beverage by brewing black tea leaves in boiling water for 5 min. About 40 elements in tea leaves and tea infusions could be determined over the wide concentration range in 8 orders of magnitude. The extraction efficiency of each element was estimated as the ratio of its concentration in tea infusions to that in tea leaves. From the experimental results for the extraction efficiencies, the elements in black tea leaves were classified into three characteristic groups: (i) highly-extractable elements (55%): Na, K, Co, Ni, Rb, Cs and Tl, (ii) moderately-extractable elements (20 - 55%): Mg, Al, P, Mn and Zn, and (iii) poorly-extractable elements (20%): Ca, Fe, Cu, Sr, Y, Zr, Mo, Sn, Ba and lanthanoid elements. Furthermore, speciation of major-to-trace elements in tea infusions was performed by using a combined system of size exclusion chromatography (SEC) and ICP-MS (or ICP-AES). As a result, many diverse elements were found to be present as complexes associated with large organic molecules in tea infusions.