Quantitative Determination of Compound Classes in Jet Turbine Fuels by High Performance Liquid Chromatography/Differential Refractive Index Detection. Part 2.

Abstract : Recent investigations demonstrated the usefulness of high performance liquid chromatography/differential refractive index detection (HPLC/DRI) as a method for quantitating compound classes present in jet fuels. The method is fast, precise and accurate when applied to mixtures of known compounds typical of each compound class encountered in a fuel. It is also accurate when the refractive index of the fuels class and the detector calibration standard are matched. This study assess the accuracy of HPLC/DRI when the calibration standards are pure compound blends whose refractive index for each compound class is matched closely to that of the fuels being analyzed. The accuracy of analyses by this method of calibration was checked by analyzing test fuels of known refractive indices. The test fuels were prepared by recombination of previously separated fuels after measuring the refractive index of each fraction. The composition of fifteen fuels was also determined by the Fluorescent Indicator Absorption (FIA) method (ASTM-D-1319-77). In general the agreement between FIA AND HPLC/DRI was quite good for many samples after conversion of the FIA aromatic content to weight percent. Four fuels, three of which have unusually high dicyclic aromatic content did not give good agreement between the two methods of analysis. The results demonstrate that it is possible to accurately calibrate the detector's response factors for each compound class by standards derived from pure compounds. To ensure that the accuracy of the results falls within the limits of the electronic integrator's precision, one needs to match the refractive index of the saturate fraction to within approximately 0.004 RI units.