Determination of Cu, Ni, Mn, and Pb in diesel oil samples using reversed-phase vortex-assisted liquid-liquid microextraction associated with energy dispersive X-ray fluorescence spectrometry

A method was developed based on reversed-phase vortex-assisted liquid-liquid microextraction (RP-VALLME) combined with energy dispersive X-ray fluorescence (EDXRF) spectrometry for the determination of Cu, Mn, Ni, and Pb in diesel oil samples. In this procedure, a nitric acid solution was used as the extraction phase to isolate analytes from organic samples. After a centrifugation step, the aqueous phase was added dropwise to a filter paper disc for EDXRF determinations. The following variables were optimized: type of extraction phase solution, concentration of the extraction phase, stirring time, and sample volume. Some instrumental parameters were also evaluated: atmospheric condition, irradiation energy, and irradiation time. Using 100 mu L of a 0.075 mol L-1 nitric acid solution as the extraction phase for a sample volume of 5.0 mL and a stirring time of 45 s, the limits of detection were 14, 8, 10, and 7 mu g L-1 for Cu, Mn, Ni, and Pb, respectively. The enrichment factors obtained were 34 (Cu), 62 (Mn), 59 (Ni), and 64 (Pb). The precisions, expressed as relative standard deviations (RSDs, %), were calculated from ten replications of the experiment under optimized conditions using standard solutions containing 200 mu g L-1 and 400 mu g L-1 of all four analytes and ranged between 2.1 and 6.4%. The results of recovery tests ranged from 87 to 112%. The proposed procedure was efficiently applied to the determination of the four analytes in diesel oil samples. The results were compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) after sample digestion, and no significant differences were found.

Automated summary

A method combining RP-VALLME and EDXRF was developed for the determination of Cu, Mn, Ni, and Pb in diesel oil samples, showing low detection limits, good precision, and high recovery rates. This method proved to be efficient and comparable to ICP-OES for the analysis of the four analytes.