Applicability of microwave induced plasma optical emission spectrometry for wear metal determination in lubricant oil using a multinebulizer

In this work, the determination of metals (i.e., Al, Cr, Cu, Mn, Ni and V) in engine lubricating oils by microwave induced plasma atomic emission spectrometry (MIP OES) has been revisited. For this purpose, a new multinebulizer in combination with the standard dilution analysis (SDA) calibration methodology has been used. The microwave plasma is very unstable and may even be extinguished when organic solvents are directly introduced. This problem can be avoided by the synergetic combination of SDA calibration and the new multinebulizer since it allows the determination of analytes in complex matrices due to the simultaneous introduction of organic and aqueous solutions, favoring plasma stabilization. Furthermore, SDA calibration also corrects the matrix effects associated with complex matrices. For the purpose of comparison, the same study has been performed using conventional calibration methodologies (i.e., external calibration (EC), internal standard calibration (IS) and standard addition calibration (SA)). To compare the calibration performances, the analytical figures of merit (i.e., limit of detection and limit of quantification) and the accuracy (i.e., trueness and precision) of the results have been evaluated. The results obtained show very similar values for SDA calibration compared to the other calibrations with a much lower consumption of reagents and resources and with a higher easiness of operation. In addition, the total analysis time has also been evaluated, which has emphasized the great advantage of the synergetic association of SDA calibration with the multinebulizer in chemical analysis using MIP OES.

Automated summary

This study revisits the determination of metals in engine lubricating oils using microwave induced plasma atomic emission spectrometry (MIP OES). A new multinebulizer and the standard dilution analysis (SDA) calibration methodology were utilized to overcome the instability of the microwave plasma caused by organic solvents. The results show that SDA calibration performs similarly to conventional calibration methods, but with lower reagent consumption, easier operation, and shorter analysis time when combined with the multinebulizer.