Determination of Cd, Cu, Ni, and Pb in Black Tea from Saudi Arabia using Graphite Furnace Atomic Absorption Spectrometry after Microwave-Assisted Acid Digestion

Abstract

A method has been developed for the determination of Cd, Cu, Ni, and Pb in black tea samples from Saudi Arabia using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS). It was found that chemical modifiers were not required for this analysis. The determination of Cd and Cu was free of spectral interferences. In the case of Ni, a strong iron line appeared close to the main nickel line, and in the case of Pb, the well-known absorption spectrum of the PO molecule was present, both of which would cause spectral interferences when deuterium background correction is used. This kind of fine-structured absorption does not cause any problems in HR CS GFAAS, as the analytical lines were separated from the background absorption. The optimum pyrolysis temperatures were 600, 1100, 1300, and 700°C and the atomization temperatures were 1200, 2000, 2550, and 1700°C for Cd, Cu, Ni, and Pb, respectively. The limits of detection were 0.03 µg L⁻¹, 11 µg L⁻¹, 0.9 µg L⁻¹, and 0.27 µg L⁻¹ for Cd, Cu, Ni, and Pb, respectively; the limits of quantification were 0.1 µg L⁻¹, 33 µg L⁻¹, 2.8 µg L⁻¹, and 0.8 µg L⁻¹ for Cd, Cu, Ni, and Pb, respectively. The results of the analysis of a green tea certified reference material confirmed the validity of the proposed method. The concentrations of Cd, Cu, Ni, and Pb found in this study were among the lowest reported in the literature for tea samples.

Keywords:

• Black tea
• Heavy metals
• High-resolution continuum source graphite furnace atomic absorption spectrometry
• Spectral interference

Acknowledgments

The authors are grateful to Analytik Jena for the loan of the high resolution continuum source atomic absorption spectrometer. A. A. Shaltout and M. S. Abdel-Aal are grateful to the Deanship of scientific research, Taif University, Saudi Arabia. The authors are also grateful to Conselho Nacional de Desenvolvimento Científico and Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil, for financial support. B. Welz has a research scholarship from CNPq and I.N.B.C has a scholarship from CAPES.

Notes

^a Cd.

^b Cu.

^c Ni.

^d Pb.

Note: All values in µg g⁻¹.

Note: All values in µg g⁻¹.

Note: All values in µg g⁻¹.

^a ND = not determined.