PERFORMANCE OF DICARBOXYLIC ACIDS AS MOBILE PHASES FOR ARSENIC SPECIATION ANALYSIS BY HPLC-ICP-MS

SIMONETTO, CANDELA; JONATAN SCHLOTTHAUER ; JUANA PEDRO; DIANA MAGNI; MIRNA SIGRIST

Mendoza

Congreso; Rio Symposium on Atomic Spectrometry; 2019

Universidad Nacional de Cuyo/CONICET

In this work, the use of dicarboxylic acids as mobile phases for the separation of four As species (arsenite (As (III)), arsenate (As (V)), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA)) by strong anion exchange chromatography was studied.The acids studied were oxalic, malonic, succinic, adipic, malic, tartaric and tartronic acid, at a pH of 8.3, in which all of the mobile phases studied have their acids groups fully deprotonated. The study was performed under isocratic conditions at a concentration of 10 mmol L-1, with a flow rate of 1 ml min-1, and an injection volume of 100 µL. Aqueous multi-species standards of As(III), DMA, MMA and As(V) at a concentration of 10 µg L-1 were used. The detection was made by ICP-MS monitoring 75As. The chromatographic parameters studied were retention factor (k), asymmetry factor (Af) and number of theoretical plates as a measure of the chromatographic efficiency (N).The greatest differences for k were observed in the case of As(V), especially with adipic acid that resulted in k values markedly lower. Regarding the Af, different behaviors were observed for the different species. For the inorganic species, which are more hydrophilic, an increase of the Af was observed with the more hydrophobic organic acids. In contrast, for DMA, a less hydrophilic species, an inverse behavior was observed. In the case of N, the chromatographic efficiency decreased with the hydrophobicity of the organic acid for the different species, with the exception of DMA whose chromatographic efficiency increased. Acids substituted with -OH in all non-carboxylic carbons, gave similar or better separations than oxalic acid, allegedly due to a masking effect of the -OH on the hydrophobic carbon chain. Of the species studied, As(V) was the most affected by the different mobile phases.Although in general DMA showed a different behavior than the other species, its chromatographic parameters exhibited subtle variations respect to those of the other species with the mobile phases studied. Based on this, oxalic and tartronic acids presented the best performance. However, in addition to being a rather uncommon reagent, tartronic acid presented a line base 3 orders of magnitude higher than oxalic acid. Therefore, oxalic acid proven to be the best alternative for the separation of the studied species.