Determination of metals in lubricating oils by X-ray fluorescence spectrometry.

The determination of common wear metals, namely iron, chromium, copper, zinc and lead, in a wide range of lubricating oil samples was investigated for the use of a low-cost, wavelength-dispersive X-ray fluorescence spectrometer. The procedure provided results in satisfactory agreement with inductively coupled plasma spectrometry used as reference method after microwave digestion of the samples in concentrated nitric acid. Statistical tests following extensive regression analyses of the data indicated that interelement effects were not statistically significant and that a simple linear regression was adequate for the calibration of individual metals.