Determination of chromium in urine by electrothermal atomic absorption spectrometry using different chemical modifiers

Abstract

The effects of the chemical modifiers Eu, Mg(NO ₃ ) ₂ , Pd, Eu-Pd and Ni and the use of longitudinally (with deuterium lamp background correction) and transversally (with Zeeman effect background correction) heated atomizers on the determination of chromium in urine samples were studied. When longitudinally heated atomizers were used, the background absorption was too high for the addition of most species, such as Mg(NO ₃ ) ₂ , Pd, Eu-Pd and Ni, rendering its use unsuitable for the determination of chromium in urine. The addition of Eu led to lower background signals. However, when longitudinally heated atomizers were used larger background absorption signals were observed on addition of a modifier. In contrast, with transversally heated atomizers the background absorption signals were low and were not influenced by the addition of a modifier, except when Mg(NO ₃ ) ₂ was added. In this case, the atomization signal shapes and the sensitivity were improved. The characteristic masses (m ₀ ) and limits of detection (3σ) were 2.2 and 3.3 pg and 0.02 and 0.04 µg Cr l ^–1 for the longitudinally (using Eu as modifier) and transversally [using Mg(NO ₃ ) ₂ ] heated atomizers, respectively. Recovery studies and analysis of standard reference materials certified for chromium were performed to asses the accuracy. The results for the determination of chromium in real samples with both background correction procedures agreed well with a precision between 0.8 and 2.5%. Both procedures can be recommended and the choice will depend on instrument availability.