Identification and Quantification of Phosphate Ester-Based Hydraulic Fluid in Jet Fuel

Phosphate ester-based hydraulic fluids are commonly used in aviation, due to their fire-resistant properties. However, contamination of jet fuel with hydraulic fluid may cause serious engine failure, hot corrosion of metals, and swelling of elastomer and polymer seals. Identifying and quantifying hydraulic fluids in jet fuels using chromatography is challenging since common hydraulic fluids, such as ExxonMobil^™ HyJet^™ V and Skydrol^™ LD-4, are composed of tri-butyl phosphate, the main peak of which overlaps with peaks from jet fuels in chromatograms. In this work, three techniques to separate and differentiate the jet fuel peaks from the tri-butyl phosphate peaks were developed. Two methods are based on a solid phase extraction (SPE) procedure followed by identification and quantification, which is carried out using a gas chromatograph equipped with a mass spectrometer or a flame ionization detector. The third technique is single-staged, where the separation and analysis are carried out by a gas chromatograph equipped with a polar column and a mass spectrometer. Lowest level of detection reached was 0.1 ppm of tri-butyl phosphate in jet fuel, 10 times lower than the limitations. Linearity was achieved in all analysis methods up to contamination of 100 ppm.