Speciation of inorganic As and Sb in natural waters by total reflection X-ray fluorescence following selective hydride generation and trapping onto quartz reflectors coated with nanostructured Pd

Abstract

In this work, a novel analytical approach for the speciation of inorganic As (iAs) and inorganic Sb (iSb) by total reflection X-ray fluorescence based on the selective generation of arsine and stibine followed by trapping onto quartz reflectors containing immobilized palladium nanoparticles (Pd NPs) is developed. Pd NPs were synthesized by chemical reduction under mild conditions (i.e., a water : ethanol mixture was used as the reducing agent) and immobilized onto quartz substrates following the silanization strategy with 3-mercaptopropyltrimethoxysilane. For microextraction and preconcentration of iAs and iSb, volatile hydrides generated in a continuous flow system were flushed onto the immobilized Pd NPs for catalytic decomposition at ambient temperature. A 2⁶⁻²_III factorial fractional design was used for screening the effect of the variables involved in the hydride generation and preconcentration steps. Selective trapping of As(III) and Sb(III) was accomplished following arsine and stibine generation under different reaction conditions, i.e., selective determination of As(III) in citric acid/citrate buffer medium (pH 4.5) and selective determination of Sb(III) in a highly acidic medium (pH < 2). In addition, As(V) and Sb(V) were pre-reduced to As(III) and Sb(III) with a KI–ascorbic acid mixture for simultaneous determination of total iAs and total iSb. The As(V) and Sb(V) contents were estimated by the difference between both measurements. Limits of detection (LODs) of 0.09, 0.10, 0.50 and 0.80 μg L⁻¹ for As(III), As(V), Sb(III) and Sb(V) were obtained, respectively. Overall efficiencies of 75% for iAs and 80% for iSb were obtained. Speciation analysis of iAs and iSb in natural waters at the sub-ppb level is demonstrated.