A green single-tube sample preparation method for wear metal determination in lubricating oil by microwave induced plasma with optical emission spectrometry

Abstract

A straightforward and rapid single-tube sample pretreatment for wear metals determination in used lubricating oils was developed in this work as an alternative to the reference pretreatment method (ASTM). A D-optimal mixture design on a three-component solution was performed. The optimal composition for the proposed sample preparation emulsion was 2% v/v of xylene, 9.5% v/v of Triton® X-114% and 88.5% v/v of H2O. The determination of 18 wear metals was carried out by microwave induced plasma with optical emission spectrometer (MIP OES), and the results of the two sample preparations -conventional and proposed- were statistically compared. Also, a certified standard “wear metals in used lubricating oils” for pretreatment validation was used. The developed method was as effective as the reference method indicated by ATSM, similar in speed and simplicity, but superior from the environmental and economic point of view. The proposed pretreatment allowed Ag, Al, Ba, Ca, Cd, Cr, Cu, K, Mg, Mn, Mo, Ni, Pb, Si, Sn, Ti, V and Zn determination, with LOQ between 1.40 mg kg−1 for Ca and 6.34 mg kg−1 for Pb. The precisions established as the relative standard deviation (RSD) were better than 6.2%. The proposed method avoid sample handling, reducing contamination risks and analyte losses, affording significantly improvement on wear metal quantification.