Speciation of arsenic and selenium compounds by ion-pair reversed-phase chromatography with electrothermic atomic absorption spectrometry - Application of experimental design for chromatographic optimisation

An off-line system is proposed consisting of ion-pair reversed-phase liquid chromatography, collections of fractions at the outflow of the column and furnace atomic absorption spectrometry. The so-called system allowed determ ination of both arsenic and selenium species mainly found in the environmen t and in mammals (arsenite, arsenate, monomethylarsonate, dimethylarsinate, selenite, selenate, selenocystamine, selenocystine, selenomethionine and s elenoethionine). In order to study the retention behaviour of these compoun ds and to estimate the optimal conditions for the chromatographic separatio n, central composite designs were used to evaluate the influence of the elu ent parameters such as pH, tetrabutylammonium phosphate (TBA) concentration and sodium hydrogenphosphate amounts. The retention factors of each specie s and the selectivity were established as response criteria. Response surfa ces and isoresponse curves were drawn from the mathematical models and enab led one to determine the optimal conditions and to visualise the method rob ustness. The predicted optimal zone was situated at pH 5.5-6.5, 4.0 mM Na2U PO4 and 3.0-4.0 mM TBA. Regression models suggested linearity for the studi ed compounds in the range 25-200 mug selenium and arsenic per litre investi gated. (C) 2001 Elsevier Science B.V. All rights reserved.