Abstract
M.Sc.
Emulsions are not widely used in industry for wear-metal-in-oil determinations and this study
was undertaken in order to evaluate such a possibility. The use of emulsified standards was
compared to aqueous standards for the calibration of an emulsified used lubricating oil sample.
The traditionally used methods of ashing in a muffle furnace and dilution with the organic
solvent, xylene were also evaluated in comparison with the emulsion methodology. Inductively
coupled plasma optical emission spectrometry (ICP-OES) was used for the wear-metal-in-oil
analysis. The performance characteristics of each method were compared for the following
metals: AI, Cr, Cu, Fe, Ni, and Pb. The used oil sample and emulsified standards were acid
treated and emulsified in water {1% wlw) using tetralin as solvent and triton X-100 as
surfactant. This evaluation included the calibration characteristics, precision and accuracy
obtained, as well as the results of recovery studies. The emulsification method was found to be
comparable to the ashing and dilution methods in terms of calibration and only Cr, Cu, Fe and
Pb concentrations were found. The precision of the emulsification method was found, in
general, to be close to or less than 2% RSD. The used oil matrix also contained leaked
petroleum from a problem car engine. An accurate determination of lead was consequently
impossible since the high lead content led to sedimentation.
The use of the internal standard, indium, was evaluated for its effectiveness in correcting
possible matrix effects that were evident from the results obtained in the recovery studies. The
recovery studies showed the Cr and Pb determinations to be adversely affected by internal
standardization. An alternative approach for matrix effect correction, the common analyte
internal standardization (CAIS) method was also investigated. This method held promise for
allowing the use of aqueous standards, instead of oil or emulsion standards, for the calibration
of the emulsified oil samples. Three different applications of the CAIS technique were
investigated and all proved unsuccessful.