Combined effect of borohydride hydrolysis and chemical additives on lead determination by CVG in the presence of transition metals

Abstract

The aim of this investigation was to increase the tolerance limit of plumbane generation towards several transition metals by exploiting the hydrolysis products of borohydride – the hydridoboron intermediates (BH) – as a derivatization reagent instead of borohydride, alone or together with chemical masking agents (oxalic acid and thiourea). The BH intermediates were produced online at 0.1 mol L⁻¹ HCl sample acidity in the presence of K₃[Fe(CN)₆] (0.1 or 1% m/v) and by varying the hydrolysis coil volume (0–2000 µL) before mixing with the analyte. The simple use of BH intermediates alone obtained with 1500–2000 µL hydrolysis coil volume allowed the achievement of tolerance limits of 100 mg L⁻¹ for Ni(II), Co(II), and Fe(III) and 105 mg L⁻¹ for a mixture of Cr(III)/V(IV)/Mo(VI) (75 + 15 + 15 mg L⁻¹). The tolerance to the strong interfering action of Cu(II) was considerably improved but limited to 2 mg L⁻¹. To mitigate the interference caused by 1000 mg L⁻¹ Fe(III), BH intermediates were used in combination with thiourea and oxalic acid. However, this approach did not enhance the tolerance to Cu(II) (2 mg L⁻¹), even in the presence of the masking agents. The established conditions allowed for the accurate determination of Pb in the complex matrix of SRM 663 (Cr–V steel) after sample dissolution with inorganic acids at high temperature.