Non-destructive elemental analysis of herbal teas from South Africa

Abstract

The elemental analysis of tea is essential since it is a commonly consumed beverage around the world. In this paper, non-destructive energy dispersive X-ray fluorescence spectrometry (EDXRF) using a standardless method based on fundamental parameters was applied in honeybush and rooibos analysis. Tea samples were measured directly in the form of loose powders. The observed element concentrations (mg kg−1) were as follows: Ca (1260–3990), Cl (914–7710), K (2270–7190), Mg (374–2510), S (474–1320), P (183−1210), Si (303−1580), Al (92–765), Fe (67–514), Mn (26–163), Cr (1.8–20), Cu (2.2–11.5), Ni (1.1–5), Rb (0.8–8), Sr (5.4–24.5), Ti (4.1–39), and Zn (4.2–18.6). What is more, the determined concentrations (mg kg−1) of selected elements in rooibos and honeybush, are statistically different: Cl (2200–7710 rooibos and 913.7–2160 honeybush); Mg (1232–3465 rooibos and 535.9–1030 honeybush); P (388.0–1566 rooibos and 244.0–403.6 honeybush); Br (12.1–52.8 rooibos and 1.6–5.3 honeybush). Multivariate analysis of variance (ANOVA) was successfully applied to the data, showing statistical significance of the concentration differences for all the elements in both types of tea. The developed method provided good precision (RSD < 6%) with an accuracy of more than 90 %, and LOD ∼ 0.5 mg kg-1- for trace elements. The method was validated using suitable certified reference materials of tea (CRM).