The present invention provides a method for the quantitative determination of contaminants in the form of fatty acid esters in jet fuels, wherein the analyte is the fatty acid ester fatty acid methyl ester (FAME) and/or the fatty acid ester fatty acid ethyl ester (FAEE), wherein the analyte undergoes a chemical reaction which is selective for it and which influences the intensity for the carbonyl band of the respective ester group with the formation of a modified analyte and the variation in the concentration of analyte in the sample, which is the jet fuel together with FAME and/or FAEE, is measured using the reduction in the intensity of the carbonyl band and/or the increase in the concentration of the modified analyte is measured using the increase in the intensity of a band which is characteristic for the modification.