Determination of chromium(III) and chromium(VI) in river water by electrothermal atomic absorption spectrometry after sorption preconcentration in a microwave field

Abstract

A rapid and sensitive method for the differential determination of Cr"' and Crv' in river water is described. Chromium species can be separated by sorption on a polymeric Detata sorbent containing conformationally flexible aminocarboxylic groups. Preconcentration using either static or dynamic conditions is possible. Microwave heating energy was used to promote the sorption. Quantitative sorption of CrI" was achieved at pH 7, and that of Crvl at pH 3; hence, complete isolation of the two forms of Cr is possible. The optimum conditions (flow rate and sorbent volume) for sorbent extraction of Cr"' and Crvl were evaluated. The technique developed is based on the ability of the sorbent to preconcentrate Cr rapidly under dynamic conditions in the presence of a microwave field. Determination of Cr by electrothermal atomic absorption spectrometry is possible either after desorption or directly in the sorbent phase. The detection limit (based on the 3s criterion) is 30 ng 1-1; the technique is characterized by high reproducibility.

Literature study of microwave-assisted digestion using electrothermal atomic absorption spectrometry

“…For chromium, comparable drying and ashing temperatures have been reported by various authors [20,25,35,47,51] and in some cases with a 2-step ashing [35,47]. The atomization temperature is found to vary between 2300 to 2600°C.…”

“…ETAAS by itself provides a very limited potential for speciation, as reflected in the appearance of publications [47]. Speciation of Cr in river water with microwave preconcentration of Cr(III) and Cr(VI) on a sorbent followed by their determination in the eluates provides a unique example in this regard.…”

“…In a recent work, a rapid and sensitive method for the speciation of Cr(III) and Cr(VI) in river water was described by Kubrakova et al [47]. Chromium species can be separated by sorption on a polymeric Detata sorbent containing conformationally flexible aminocarboxylic groups.…”

“…Some authors reported the use of BGC [25,35] for Cr. Although most of the workers did not use a modifier [20,25,35,47], some authors compared the chromium determination with various modifiers and without any modifier [51].…”

“…On the other hand, some authors [24,27,28] have recommended the use of a catalyst like V O which may lead to some contamination problems. Nevertheless, an interesting development has been the use of microwave treatment of small samples [1,15,37,40,47] and also the use of flow injection systems and on-line mineralization.…”