Determination of copper, iron, aluminium, lead and cadmium in cork stoppers by electrothermal atomic absorption spectrometry

Abstract

Methods for the determination of five elements (Cu, Fe, Al, Pb and Cd) in cork stoppers by electrothermal atomic absorption spectrometry (ETAAS) with a stabilized temperature platform furnace are described. A previous acid digestion of the cork stoppers in HNO₃–HCl–HF in poly(tetrafluoroethylene) apparatus, was required owing to the specific and characteristic nature of cork. The digests were evaporated to dryness and the residue was dissolved in HNO₃ for subsequent measurement by ETAAS. Depending on the metal, a suitable chemical modifier was added when necessary, i.e., Mg(NO₃)₂ for Al and Fe, a mixture of Mg(NO₃)₂ and Pd(NO₃)₂ for Pb and NH₄H₂PO₄ for Cd. The linear ranges for determination were 0.6–50, 0.8–50, 1.5–50, 1.1–75 and 0.4–2.0 µg l^–1 for Cu, Fe, Al, Pb and Cd, respectively, after appropriate dilution. For precision and recovery studies, several determinations (from six to ten) for each of the five metals were conducted on different aliquots of the same sample, using the standard additions method at three specific concentrations. The relative standard deviations were 11.4, 9.4, 15.0, 9.5 and 7.1% for Cu, Fe, Al, Pb and Cd, respectively, which makes this method satisfactory and suitable for routine analysis.