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.

Simultaneous determination of copper and iron in automotive gasoline by X-ray fluorescence after pre-concentration on cellulose paper.

This paper proposes an alternative analytical method using energy dispersive X-ray fluorescence (EDXRF) to determine Fe and Cu in gasoline samples. In the proposed procedure, samples were distilled and the distillation residues were spotted on cellulose paper disk to form a uniform thin film and to produce a homogeneous and reproducible interface to the XRF instrument. The disks were dried at 60 degrees C for 20min and copper and iron were determined directly in the solid phase at 6.40 and 8.04keV, respectively. The calibration curves showed linear response in the 20-800mugL(-1) concentration range of each metal. The precisions (repeatability) calculated from 15 consecutive measurements and defined as the coefficient of variation of solutions containing 100mugL(-1) of Fe and Cu were 7.8 and 8.1%, 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 10 and 15mugL(-1) for Fe and Cu, respectively. The proposed method was applied to copper and iron determination in gasoline samples collected from different gas stations.