Determination of Wear Metals in Used Motor Oil by Flame Atomic Absorption Spectroscopy

Abstract

For decades, railways, trucking companies, and commercial airlines have utilized oil analysis as a diagnostic tool to prevent engine-component failures. This interesting application was developed into an undergraduate lab experiment to introduce chemistry and environmental science majors in their second to fourth year to metal analysis using flame atomic absorption spectroscopy with a non-aqueous sample matrix. Copper, lead, iron, chromium, and silver were quantified by the method of standard additions or by external calibration curves with matrix matching. Students in both environmental analysis and analytical chemistry courses used their data to assess the health of a vehicle's engine.

Designation of Chosen Heavy Metals in Used Engine Oils Using the XRF Method

“…Even though these are admissible amounts when it comes to ecotoxicity and phytotoxicity, the elevated content of lead in the soil may pose a threat to human beings, and especially to children [24]. Lead is removed from base oils, hence its presence in used oils is mainly connected with bearing wear [26,27], but the contamination source may also be fuel. This, however, pertains mainly to petrol-fuelled engines [28].…”

“…However, it also is subject to strong bioaccumulation, particularly in phytoplankton, which effects its fast incorporation into the food chain [24]. In used oils nickel mainly comes from the piston rings and the shaft [27]. The content of nickel found in the analysed samples ranged from 0.14 to 0.75 mg·kg -1 (on average 0.38 mg·kg -1 ).…”

“…Tin is entirely removed from base oils since it is considered contamination, therefore its presence in used oil results from the wear of the shaft, bearings, guides, and sleeves [26,27]. In the analysed oils tin was noted in three samples.…”

“…Due to the relatively high copper bioconcentration factor and high level of its anthropogenic deployment, it poses a significant threat of local biological contamination [24]. Copper in used oils comes mainly from the wearing products of the bearings, rings, and valve guides; in smaller quantities it is introduced in the form of additives [26,27] . The content of Cu in one of the samples caused an extremely high value of variation coefficient, which exceeded 95%.…”

“…It is the basic active element of hightemperature antioxidation additives. It can also be found in the composition of antiwear additives or corrosion inhibitors added to engine oils [26,27]. The increase in the content of zinc in used oils in comparison with fresh oil may be the result of the presence of wearing products.…”