Multielemental determination in lubricating oil samples by microwave-induced plasma optical emission spectrometry after extraction induced by emulsion breaking

Abstract

Extraction induced by emulsion breaking (EIEB) was studied as a strategy for the determination of Al, Cr, Cu, Fe, Mg, Mn, Mo, Ni, and Pb in used lubricating oil via microwave-induced plasma optical emission spectrometry (MIP OES). No spectral or nonspectral interferences were observed in the developed method. These were evaluated as a function of the emission intensity of natural molecular species in the N2 plasma and different atomic and ionic emission lines. The time required for extraction was evaluated, and the best sensitivity for all the elements was obtained at 40 min of contact between the sample and the extraction solution in the presence of the surfactant. Doehlert matrix response surface methodology was employed to study the effects and interactions between the nitric acid (extractor) and surfactant (emulsifier) concentrations during sample preparation. The recommended conditions for 3.0 g of sample were as follows: 5.0 mL of extraction mixture consisting of 2.8 mol/L nitric acid and 3.0 % (v v−1) of the surfactant Triton X-114. The limits of quantification obtained were 2.9 (Al), 43 (Cr), 4.0 (Cu), 17 (Fe), 4.0 (Mg), 3.7 (Mn), 7.0 (Mo), 9.2 (Ni) and 45 (Pb) µg kg−1. The method developed was applied in the analyses of lubricating oil samples. The following concentration ranges (mg kg−1) were found: 2.5–106 (Al), 2.8–24.8 (Cr), 3.5–21.4 (Cu), 16.9–199 (Fe), 33.4–64.0 (Mg), 0.57–9.7 (Mn), 4.7–43 (Mo), 1.6–11.1 (Ni) and 2.0–12.6 (Pb).This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors are also thankful to the Fundação de Amparo a Pesquisa do Estado da Bahia (FAPESB) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the provision of grants, fellowships, and financial support