Development of a rapid-test method for the determination of calcium, zinc, phosphorus, and sulfur in automotive engine oil by WD-XRF (wavelength dispersive x-ray fluorescent)

Abstract

This study describes a rapid method for the determination of calcium, zinc, phosphorus, and sulfur in lubricating oil products using WD-XRF (Wavelength Dispersive X-ray Fluorescent). Currently, there are several normative references appointed by the mandatory SNI (Indonesian standard) used for elemental analysis in automotive engine oils, i.e., ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectroscopy), AAS (Atomic Absorption Spectrophotometry) for calcium, zinc, or magnesium; ED-XRF (Energy Dispersive X-ray Fluorescent) for sulfur, lamp method for sulfur, and quinoline phosphomolybdate method for phosphorus. The wet chemical analysis principle used in those reference methods (AAS, ICP-AES, and conventional method) needs a sample preparation step before the main instrument can use to measure an oil sample. It is a time-consuming process and commonly consists of a few steps such as dilution, weighing, heating, and destruction. The statistical characteristics (limit of detection, the limit of quantification, precision, accuracy, and linearity) obtained in this experiment were relatively acceptable. Elemental analysis by WD-XRF needs no sample preparation process, fast, less chemical reagents, multi-elements, simultaneously, and simple. The WD-XRF method potentially could be used as an alternative method for the determination of certain elements (Ca, Zn, P, S) or more as specified in the mandatory SNI for automotive engine oil products.