Determination of wear metals in lubricating oils using flow injection AAS

The feasibility of flow injection analysis (FIA) was explored for the deter mination of wear metals in used lubricating oil by atomic absorption spectr ometry. The difficulty presented by the viscosity of the samples was overco me by injecting the oil sample with a lab-made motorized syringe into a str eam of kerosene. In order to achieve a thorough mixing of the two streams, 3 specially packed reactor was designed. The stream carrying the diluted sa mple was then carried to an AA spectrometer. A computer-controlled system w as developed for injection and data acquisition allowing partial automation of the process. The influence of several parameters (sample and carrier flow rates, reactor length) was studied. Copper and iron were chosen as model analytes. Calibration was performed wi th Conostan standards diluted with unused oil. The accuracy was evaluated b y analyzing real oil samples for copper and iron in the range of 1 to 40 pp m. The results were compared with those obtained by AAS measurement with ma nual dilution, using the joint-confidence ellipse F-test for the regression straight-line. No significant differences were found at the 95% confidence level. Precision of the results was 2.6% (RSD). The analytical frequency attained was 30 hour(-1), which could be doubled w ith some software modifications. The stability of the proposed system was d emonstrated during a 60-minute test, finding no evidence of drift in either baseline or sensitivity.