Zinc determination in Tannat wine by direct injection onto graphite tube: Electrothermal AAS as an alternative to flame AAS

A novel method was developed for the determination of zinc in wine by direct-injection electrothermal atomic absorption spectrometry (ETAAS). Unlike the ON (Organisation Internationale de la Vigne et du Vin) reference method, which is based on flame atomic absorption spectrometry (FAAS), the proposed method does not require any sample preparation. Previous to the development of this method a reappraisal of the possible interferences found during the determination of zinc in wine by the reference ON method was undertaken. Aiming at minimising sample preparation during FAAS method, alternatives such as the use of matched-matrix standards and the use of the Standard Additions Method (SAM) were studied, however different samples of Tannat wine produced in Uruguay exhibited widely different interference patterns, precluding the possible development of an alternate sample preparation free FAAS method. Thus a new method based on direct-injection ETAAS was developed. The method is based on the atomic absorption of zinc at the alternate resonance wavelength of 307.6 nm. Samples are injected in the graphite furnace without preparation and the determination carried out by SAM. Quantification limit was 0.10 mg L-1 and linearity was confirmed in the range 0.10-10 mg L-1. Precision (repeatability, s(r) (%), n = 5) was calculated at three concentration levels and found to be better than 5%. When compared with the ON reference method, results agreed within 10%. The method is fit for the purpose of routine analytical quality control, requiring no sample preparation and thus less labour and producing less chemical waste. (C) 2017 Elsevier B.V. All rights reserved.