Oxidation state specific generation of arsines from methylated arsenicals based on l-cysteine treatment in buffered media for speciation analysis by hydride generation-automated cryotrapping-gas chromatography-atomic absorption spectrometry with the multiatomizer

Abstract

An automated system for hydride generation -cryotrapping-gas chromatography -atomic absorption spectrometry with the multiatomizer is described. Arsines are preconcentrated and separated in a Chromosorb filled U-tube. An automated cryotrapping unit, employing nitrogen gas formed upon heating in the detection phase for the displacement of the cooling liquid nitrogen, has been developed. The conditions for separation of arsines in a Chromosorb filled U-tube have been optimized. A complete separation of signals from arsine, methylarsine, dimethylarsine, and trimethylarsine has been achieved within a 60 s reading window. The limits of detection for methylated arsenicals tested were 4 ng l −1 . Selective hydride generation is applied for the oxidation state specific speciation analysis of inorganic and methylated arsenicals. The arsines are generated either exclusively from trivalent or from both tri-and pentavalent inorganic and methylated arsenicals depending on the presence of L-cysteine as a prereductant and/or reaction modifier. A TRIS buffer reaction medium is proposed to overcome narrow optimum concentration range observed for the L-cysteine modified reaction in HCl medium. The system provides uniform peak area sensitivity for all As species. Consequently, the calibration with a single form of As is possible. This method permits a highthroughput speciation analysis of metabolites of inorganic arsenic in relatively complex biological matrices such as cell culture systems without sample pretreatment, thus preserving the distribution of tri-and pentavalent species.

On-line pre-reduction of pentavalent arsenicals by thioglycolic acid for speciation analysis by selective hydride generation–cryotrapping–atomic absorption spectrometry

“…This is particularly important in biological samples, where As species are bound to proteins and can be determined without extraction and when attempting the determination of very unstable MAs(III) and DMAs(III), which are quickly oxidized to MAs(V) and DMAs(V) even at temperatures below 0 °C [11,12]. That is why this method is suitable for the speciation analysis of all above-mentioned compounds [6,13,14].…”

“…Instead of the choice of pH, the selective HG in presence or absence of pre-reduction agent has been developed in our laboratory for the arsenic speciation analysis [13,14], overcoming the different sensitivity obtained for individual species observed for pH specific generation approach [6,11,13].…”

“…Due to low stability and neccessity of high concentration of KI and HCl for reaching complete pre-reduction, agents with -SH group, namely L-cysteine (L-cys) are more popular nowadays [13,16,[21][22][23][24]. These agents reduce pentavalent arsenicals to trivalent and react with trivalent arsenicals forming arsinothiol derivates.…”

“…It has also been suggested that L-cys is enhancing the HG performance by forming borane complexes with tetrahydroborate [25]. By means of L-cys treatment uniform signals can be obtained from iAs(V), MAs(V) and DMAs(V) [13,26]. Nevertheless, optimum conditions must be carefully maintained when HG is performed from HCl media, because HG is efficient in a very narrow range of acid concentration (0.01 -0.1 M) only [13,27].…”

“…By means of L-cys treatment uniform signals can be obtained from iAs(V), MAs(V) and DMAs(V) [13,26]. Nevertheless, optimum conditions must be carefully maintained when HG is performed from HCl media, because HG is efficient in a very narrow range of acid concentration (0.01 -0.1 M) only [13,27]. This problem has been solved by the use of buffered media (TRIS·HCl buffer) proposed and studied in our previous report [13].…”