THE DETERMINATION OF WEAR METALS IN USED LUBRICATING OILS BY FLAME ATOMIC-ABSORPTION SPECTROMETRY USING SULFANILIC ACID AS ASHING AGENT

A simple and reliable ashing procedure is proposed for the preparation of used lubricating oil samples for the determination of calcium, mag nesium, zinc, iron, chromium and nickel by flame atomic absorption spe ctrometry. Sulphanilic acid was added to oil samples and the mixture c oked and the coke ashed at 550 degrees C. The solutions of the ash wer e analysed by flame AAS for the metals. The release of calcium, zinc, iron and chromium was improved by the addition of sulphanilic acid to samples. The relative standard deviations of metal concentration resul ts in the initial oil samples were 1.5% for Ca (1500 mg l(-1) level), 0.3% for Mg (100 mg l(-1) level), 3.1% for Zn (1500 mg l(-1) level), 0 .7% for Fe (500 mg l(-1) level), 0.02% for Cr (50 mg l(-1) level) and 0.002% for Ni (10 mg l(-1) level). The optimum sample size for efficie nt metal release was 20 g while the optimum sulphanilic acid to oil ra tio was 0.05 g per gram of oil for Zn and Cr and 0.10 g for Ca and Fe. Results obtained by this procedure were highly reproducible and compa rable with those obtained for the same samples using standard procedur es. (C) 1997 Elsevier Science B.V.