Identification and semi-quantitative determination of anti-oxidants in lubricants employing thin-layer chromatography-spray mass spectrometry

A quick and simple method for identification and semi-quantitative determination of nine antioxidants commonly used in lubricants is presented. A dual step thin-layer chromatography (TLC) separation, removes in a first step the oil matrix whereas in a second step the antioxidants are separated. Cutting the spots out of the TLC-plate in the form of triangles allows direct-spray mass spectrometric (MS) measurements, providing MS and MSn spectra (if an appropriate MS instrument is employed) of the antioxidants, allowing their identification but also giving information about potential oxidation or degradation of these additives. Calibration curves within the concentration range relevant for the analysis of real oil samples (0.2-1.2 g L−1) were constructed with R2 values above 0.98 (when using an appropriate internal standard). This allowed the semi-quantitative determination of the selected antioxidants in real oils samples. Comparison with results from HPLC-UV measurement showed acceptable agreement for all analytes.