Iron analyses performed on used gas turbine lubricating oil samples by several variations of rotating disk–spark emission spectrography, atomic absorptiometry, and x-ray fluorescence spectrometry are compared with a quantitative wet chemical technique. The results indicate that emission spectrography with a cobalt internal standard, atomic absorptiometry with a nitrous oxide–acetylene flame, and x-ray fluorescence, both dispersive and nondispersive, are the most reliable instrumental methods. The iron contained in the samples exists primarily as particulates 1 μ or less in diameter.
Gerald S. Golden, "The Determination of Iron in Used Lubricating Oil," Appl. Spectrosc. 25, 668-671 (1971)