Determination of the concentration of antiwear additive in diesel fuel by gas chromatography-mass spectrometry
Introduction. It was previously found that during the storage of diesel fuels, a decrease in lubricity occurs, and for different antiwear additives, the decrease occurs in different ways. Therefore, the relevant objective is to establish the effect of the fatty acid composition of antiwear additives, which were added to diesel fuel, on the change in lubricity during fuel storage. To solve this problem, a method is required that allows to determine the fatty acid composition of antiwear additives in diesel fuel. Six anti-wear additives of domestic and imported production were selected as objects of research. The study of the composition of additives was carried out by gas-chromatography-mass spectrometry. Results. The fatty acid composition of the additives was identified. A method has been proposed that allows to determine the content of essential fatty acids of antiwear additives in diesel fuel in the concentration range from 0,005 to 0,010 wt%. Discussion. A gas chromatographic column was selected that allows identifying C8-C24 fatty acids without performing the esterification step. The conditions for chromatography were selected to achieve the separation of diesel fuel components and fatty acids of antiwear additives. Different methods of recovery of anti-wear additive components from diesel fuel were compared and their conversion to esters. It has been proven that the fatty acids selected as markers, namely palmitic, oleic, linoleic and linolenic, allow the quantitative determination of antiwear additives in diesel fuel by gas chromatography-mass spectrometry without esterification. To determine the antiwear additive in low concentrations from 0.005 to 0.01 wt%, it is necessary to use solid phase extraction according both when constructing a calibration curve and when directly determining the additive in diesel fuel. Conclusion. A method has been developed that allows to quantitatively determine the content of fatty acid based antiwear additive in diesel fuel using gas chromatography-mass spectrometry without converting fatty acids into esters.