A greener sample preparation procedure using reverse-phase dispersive liquid-liquid microextraction for multielement determination of inorganic species in petroleum-derived samples

This study describe the development and first application of reverse-phase dispersive liquid-liquid microextraction (RP-DLLME) sample preparation for the determination of Ca, Cd, Cu, Fe, K, Mg, Mn, Ni, Pb, and Zn in petroleum-derived samples using inductively coupled plasma optical emission spectroscopy (ICP OES). Some factors inherent to RP-DLLME were optimized using multivariate statistical analysis through the 24 full factorial design followed by the Doehlert matrix. The established RP-DLLME procedure employs 5.0 g of samples, 1600 mu L of the 3.75% (v/v) HNO3:isopropyl alcohol [3:1 (v/v)] extractive solution, 10 min of thermostatic bath at 80 degrees C, 60 s of vortexing, 3 min of sonication at 55 degrees C, and 15 min of centrifugation at 3500 rpm. The resulting aqueous phase volume was adjusted up to 15 mL with ultrapure water, and ICP OES carried out the measurements. Relative standard deviations (RSD) less than 3.5%, linear correlation coefficients better than 0.9985, and limit of detection (LOD) in the range of 0.57 ng g-1 (Mn) to 107.6 ng g-1 (K) were obtained for the determination of the analytes. Accuracy of the RP-DLLME using ICP OES was evaluated by analysis of the V21 + K metallo-organic standard, and recovery percentages within the 89.4-98.3% interval with RSD less than 6.4% were obtained. The accuracy and precision were also evaluated through a recovery test, and the results were in the range of 87.1-95.7% with RSD less than 4.9% for all analytes. Therefore, the RP-DLLME-ICP OES methodology was successfully applied to gasoline, diesel oil, JET-A1 (jet fuel), Avgas (aviation gasoline), lubricant oil, and vaseline samples, and the contents were obtained for almost all analytes. Although there are no regulatory resolutions for all petroleum-derived samples, the content of the analytes determined in JET-A1 and Avgas samples complied with ANP Resolution No. 856/2021 and 901/2022 legislation, respectively. Furthermore, the relative simplicity of the RP-DLLME combined with the accurate and precise measurements carried out by ICP OES can be a viable alternative in routine analysis.

Automated summary

This study developed the RP-DLLME sample preparation method and applied it to the determination of multiple metal elements in petroleum-derived samples using ICP OES. The RP-DLLME procedure was optimized and evaluated through multivariate statistical analysis. The results showed that this method has good accuracy and precision, making it a viable alternative for routine analysis.