Novel and selective procedure for Cr(VI) determination by X-ray fluorescence analysis after membrane concentration

A new, simple and selective method for the determination of Cr(VI) in aqueous samples has been developed by using a combination of membrane preconcentration and energy dispersive X-ray fluorescence spectrometry. The enrichment of Cr in the membranes is accomplished by the addition of the commercial anion-exchanger extractant Aliquat 336. Two different types of membranes have been investigated: the so-called impregnated membranes, where an organic solution of the extractant fills the pores of commercial polymeric membranes, and polymer inclusion membranes, prepared by physical inclusion of Aliquat 336 in the matrix formed by either cellulose triacetate or poly(vinyl chloride) and the plasticizer 2-nitrophenyl octyl ether. Both types of membranes were found to be stable and efficient for the preconcentration of Cr, but polymeric membranes made of PVC showed a higher degree of homogeneity in terms of metal distribution. Determination of the Cr collected on the membranes was performed by means of a commercial energy dispersive X-ray fluorescence spectrometer. Parameters affecting the performance of the preconcentration method as well as the analysis of the membranes have been investigated, and a linear response has been obtained between the Cr present in the aqueous solutions and the metal extracted on the membrane. The calibration curve obtained when using PVC-based membranes was linear over the concentration range 0.3-8.8 mg L-1 with a detection limit of 0.3 mg L-1. The selectivity of the proposed method has been evaluated, and also, it has successfully been applied to the analysis of chromium present in real samples of electroplating water from galvanic baths. (c) 2006 Elsevier B.V. All rights reserved.