Wendell E. Rhine

Determination of Wear Metals in Aircraft Lubricating Oils by Atomic Absorption Spectrophotometry Using a Graphite Furnace Atomizer

Atomic absorption spectrophotometry equipped with a graphite furnace atomizer has proven to be a very effective technique for determining iron, copper, aluminum, magnesium, and other critical wear metals in lubricating oils. Oil samples are diluted 1:4 with kerosene, and 0.5–20 μL can be analyzed by direct injection into the furnace. Analytical conditions have been established for 10 wear metals. Working curves, times, and temperatures for drying, ashing, and atomizing cycles have been determined. Precision of analysis was determined for standards (dissolved) and samples containing metallic particles (undissolved). The RSDs for 10 runs of 3 ppm Fe, 1 ppm Cu, and 1 ppm Al were 10.0, 4.0, and 3.9 percent, respectively. Metal powders of Fe, Cu, and Al having maximum sizes of 5, 10, and 20–30 μm were analyzed and precisions determined. Comparative analytical results were obtained for Fe particles of 1, 3, 5, 8, 10, 12, and 20–30 μm with the use of various spectrometric techniques. The graphite furnace was shown to be superior to ICP, DCP, flame AA, and rotating disk AES. In the analysis of used oil samples, the graphite furnace gave better precision and analyzability for Fe and Cu than the other instruments considered.