Voltammetric determination of aluminum(III) as Al-Alizarin S complex in tea leaves and infusions

Abstract

This work presents, for the first time, DPV methodology of indirect aluminum (III) determination in tea leaves and infusions using the renewable silver amalgam electrode. A self-referencing strategy was proposed which relies on alternate voltammetric curves registration with and without conditioning of the electrode surface. The developed procedure utilizing formation of aluminum-Alizarin S complex shows linearity in the range of 2–50 μg L−1 of Al(III) concentration, with r > 0.997. In the case of the electrode conditioning LOD is 0.2 μgL−1 and repeatability expressed by CV is 1–2%. Introducing an additional operation i.e. electrode activation results in decrease of sensitivity from 0.0162 to 0.0043 μA/μgL−1. The method was verified using CRM (tea leaves). Due to the wide variety of tea origin, types and producers, four most popular sorts (black, green, red and white) were chosen, made by one manufacturer. It was demonstrated that the proposed methodology may be applied in Al(III) determination in tea leaves and infusions. Al(III) extraction effectiveness was also examined. It was verified, that lemon juice addition during brewing increases aluminum concentration in infusions. Using Principal Components Analysis it was demonstrated that automatic distinction of infusions brewed with and without lemon juice, based on unprocessed voltammetric signal, may be successfully realized.