Insight into the mechanisms controlling the chemical vapor generation of cadmium

Abstract

Chemical vapor generation of cadmium (CVG) by aqueous NaBH₄ was investigated with the aim to individuate the mechanisms controlling the generation of volatile cadmium species in the absence of any additive. A continuous flow reactor was employed in combination with atomic absorption spectrometry. An electro-thermal quartz tube atomizer (293–1200 K) and a miniature argon–hydrogen diffusion flame were employed as the atomizers. The reactor system can be used with various chemifold setups which allow different mixing strategies of the sample (2.5–50 μg L⁻¹ of Cd^II in 0.25 mol L⁻¹ HCl) and reductant (1–3% m/v NaBH₄ in 0.1–1.2 mol L⁻¹ NaOH) solutions. The molar ratios of the reagents HCl, NaBH₄ and NaOH play a decisive role in determining both the nature of Cd^II substrates and the hydrolysis products of BH₄⁻, which strongly affected the generation efficiency of volatile Cd species. For the first time the interference effect of dissolved oxygen and the use of BH₃OH⁻ in CVG of Cd have been demonstrated. The interference of dissolved oxygen, causing liquid phase interference during the derivatization step, can be removed by degassing the solution with argon. The on-line generation of BH₃OH⁻ in a quenched flow reactor indicates that it is more efficient than that of BH₄⁻ and it might play a role in CVG of Cd. The combination of BH₃OH⁻ derivatization and degassed solutions allows obtaining about 20 and 5 fold increase of sensitivity using a quartz tube and miniature flame, respectively. Volatile cadmium vapors are composed of both atomic and molecular species, and the oxygen removal and/or the use of BH₃OH⁻ favors the formation of atoms with respect to molecular species.