Chemical vapour generation assisted by Cr3+/KCN coupled to atomic fluorescence spectrometry for ultrasensitive determination of cadmium in water and rice samples

Abstract

A methodology for cadmium determination at ultratrace levels based on chemical vapour generation (CVG) coupled to atomic fluorescence spectrometry (AFS) was developed. Cd volatile species were generated in a four-channel flow injection CVG system by the reaction of the analyte with NaBH₄ in a HCl medium in the presence of Cr³⁺/KCN used as modifiers enhancing the CVG efficiency. An in-house assembled non-dispersive AFS was used as a detector of the volatile species in two types of flame atomizers – the miniature diffusion flame (MDF) and the flame-in-gas-shield (FIGS) atomizers. The atomization conditions were optimized for both atomizers and the tolerance towards interferences from hydride forming elements and mercury was examined. The sensitivity obtained with the FIGS atomizer was approximately twofold higher compared to that with the MDF atomizer; therefore, the FIGS atomizer was selected for further analytical applications, providing an excellent limit of detection of 0.42 ng L⁻¹ Cd (63 fg absolute). The accuracy of the proposed methodology was verified by analyses of certified reference materials of water with various matrix complexities (fresh water SRM 1643f, wastewater ERM-CA713 and seawater CASS-4 and NASS-5) and rice flour SRM 1568b after microwave digestion in a diluted acid medium with very good agreement with certified values. In addition, the practical application was successfully demonstrated by determination of Cd content in three samples of rice and rice flour with excellent agreement with the values obtained by solution nebulization inductively coupled plasma mass spectrometry.