FAAS Determination of Calcium and Zinc in Lubricating Oil with Incomplete Digestion of Sample

The lubricating oil sample was digested with conc.HNO3 under moderate heating,and the sample solution obtained after incomplete digestion was emulsified with Triton X-100 and Tween 80 to make it a homogeneous and transparent or semitransparent,yellowish orange or yellowish green colored solution.The solution was diluted to 25 mL in a volumetric flask and used for FAAS determination of calcium and zinc.Analytical conditions,including the acid and emulsifying agent used in the in complete digestion of sample as well as the chemical interferences,background interference and consistency of viscosities between blank solution and sample solution were studied and optimized.Linear relationships between the absorbance and concentration of calcium and zinc were obtained in the ranges of 0-12 mg·L-1 and 0-1.6 mg·L-1 respectively.Detection limits (3σ/s) of the method were found as 0.14 mg·L-1 (for Ca),and 0.018 mg·L-1 (for Zn).In its application to the analysis of substantial oil samples,values of RSD′s (n=6) obtained were less than 5%,and values of recovery test were in the range of 97.0%-104.8% for both elements.