The characterisation of engine oils by liquid chromatography with luminescence detection
This thesis describes the development of pre column derivatisation reactions for the selective determination of organic functional groups in oxidised oils by liquid chromatography (LC) with luminescence detection. The testing of oils for oxidative stability and the current methods of oil analysis are reviewed in chapter one. An overview of LC and luminescence spectrometry, with particular regard to chemiluminescence (CL) is also presented. Chapter two is a flow injection investigation of the experimental variables of the peroxyoxalate CL reaction. Two aryl oxalates; bis(2,4-dinitrophenyl)oxalate and bis(2,4,6-tricblorophenyl)oxalate were compared for their suitability to LC detection. A charge coupled device (CCD) was used to obtain the CL spectra of fluorophores and to investigate the CL emission background. Chapter three and four describes procedures for the determination of carboxylic acids in oils by pre column esterification with 9-anthracenemethanol, reversed phase LC and either peroxyoxalate CL or fluorescence detection. The oils were dialysed prior to derivatisation to remove high molecular weight species which were found to interfere with the reaction. Carboxylic acids were present in the oxidised oils and their concentrations reflected the degree of degradation of the oils. The determination of aldehydes in oxidised oils is described in chapter five. The aldehydes in oil dialysates are labelled by reductive amination with 3- aminofluoranthene and the derivatives separated by isocratic reversed-phase LC with peroxyoxalate CL detection using TCPO-hydrogen peroxide. Aldehydes were also found to be produced by the oxidation of oils in car engines.