Indirect determination of chloride and sulfate ions in ethanol fuel by X-ray fluorescence after a precipitation procedure.

This paper proposes an alternative analytical method using energy dispersive X-ray fluorescence (EDXRF) to determine chloride and sulfate ions in ethanol fuel samples after precipitation procedure. The preconcentration methodology involved the precipitation of the analytes as silver chloride and barium sulfate followed by filtration through a paper filter, which demonstrated to be a convenient substrate for EDXRF measurements. The elements were determined directly on the filters using silver and barium lines for the indirect determination of chloride and sulfate ions, respectively. The precisions calculated from 20 consecutive measurements and defined as the coefficient of variation of standard solutions containing 1.0 microg mL(-1) of Cl(-) and SO(4)(2-) were 7.3% and 5.9%, respectively. The limits of detection (LOD), defined as the analyte concentration that gives a response equivalent to three times the standard deviation of the blank (n=10), were found to be 25 microg L(-1) and 30 microg L(-1) for Cl(-) and SO(4)(2-), respectively. The proposed method was applied to chloride and sulfate ions determination in hydrated ethanol fuel samples collected from different gas stations.