The analysis of engine oils and engine oil additives by mass spectrometry
Chapter I presents an overview of mass spectrometry on double focusing instruments. Special attention is paid to ionisation methods which may be of use in mixture analysis. In chapter II, following a brief introduction to chemometrics, results of the application of factor analysis to the problem of determining the components of a mixture from mass spectra of simple mixtures are given. After applying the technique to simulated data, the results of applying the technique to simple mixtures and to the deconvolution of overlapping GC/MC spectra are given. It is concluded that provided the pure compounds have 'unique' peaks in their mass spectra, and that the statistical variations in the intensities of peaks due to different mixtures are not correlated, then the technique will yield good results. Chapter III deals with the application of CI techniques and factor analysis to the analysis of engine oils. Attempts to use the factor analysis technique to yield a meaningful 'type' analysis of engine oil fractions was not successful. The use of proton transfer reagents and charge transfer reagents for CI spectra of engine oil fractions was also unsuccessful. It is concluded that the complexity of engine oil mixtures and the chemical similarity of the constituent molecules makes them difficult to differentiate by CI mass spectrometry. In the final chapter, details are gave of an investigation into the use of CI mass spectrometry and FAB mass spectrometry for the analysis of engine oil additives. The additives studied were calcium 2,2'-bis (4-alkylphenyl) sulphides. The FAB mass spectrometry of these sulphurised phenates gave poor results with glycerol, triethanolamine, triethanolamine / sodium sulphate or squalane used as FAB matrix. Of the CI techniques used, electron capture ionisation of the hydrolysed sample gave the most promising results. The molecular ion peak intensities were higher than those encountered in the EI spectra. In addition, the fragmentation in the EC spectra was simpler than the fragmentation in the EI spectrum. Metastable ion studies of the EI and EC spectra of the sulphurised phenols, using the technique of metastable mapping, gave some useful results, but the poor mass resolving power and the long run times were a major drawback. It is concluded that the technique of metastable mapping is of no use where mass resolution is important, and the use of inlet systems, such as an AGHIS, which allow long sample lifetimes is recommended. Where possible, the use of tandem mass spectrometry or Fourier transform mass spectrometry for metastable ion studies for mixture analysis, is also recommended.