HPLC-AAS interfaces for the determination of ionic alkyllead, arsonium and selenonium compounds

Abstract

Three direct interfaces for coupling high performance liquid chromatography (HPLC) with atomic absorption spectrometry (AAS) were developed and optimized for the determination of ionic organolead, organoselenium and organoarsenic compounds. The first all-quartz interface consisted of a thermospray nebulizer and a flame microatomizer in which ionic alkyllead analytes (R$sb{ rm n}$Pb$sp{ rm (4-n)+};$ R = CH$sb3,$ C$sb2$H$sb5)$ were atomized by a methanol (from HPLC eluent)-oxygen kinetic flame, and channeled in a quartz tube (atom keeper) mounted into the AAS optical beam. Alternately, the classical electrothermal atomization technique for organolead species (quartz furnace under hydrogen atmosphere) was coupled with a post-column derivatization-volatilization apparatus based on the ethylation of ionic alkylleads by sodium tetraethylborate. The limits of detection provided by these two approaches were 1.0-3.4 ng and 0.10-0.15 ng, respectively. Arsonium ((CH$sb3) sb3$RAs$sp+;$ R = CH$sb3,$ CH$sb2$CH$sb2$OH, CH$sb2$COOH) and selenonium ((CH$sb3) sb2$RSe$sp+;$ R = CH$sb3,$ CH$sb2$CH$sb2$OH) species were quantified using a novel HPLC-AAS approach based on a direct coupling of three processes: thermospray nebulization, thermochemical hydride generation using hydrogen gas, and diffuse flame atomization. Direct evidences for the thermochemical hydride generation process was obtained by injecting (CH$sb3) sb3$SeI and SeO$sb2$ into the interface and capturing the gaseous end products in liquid chemical traps specific for SeH$sb2$ and Se(IV). Both analytes were derivatized to SeH$sb2$ only in the presence of hydrogen in the interface. Reverse- and normal-phase high pressure liquid chromatographic methods were also developed and adapted for the HPLC-AAS analyses of alkyllead, arsonium and selenonium compounds in real samples. The limit of detection of the arsonium and selenonium cations were 7.6-13.3 ng and 31.0-43.9 ng, respectively