Identification and quantification of phosphate ester-based hydraulic fluid in jet fuel

Phosphate ester-based hydraulic fluids are commonly used in aviation, among others due to their fire resistance properties. However, they also cause corrosion of metals and swelling of elastomer and polymer seals. Contamination of jet fuel with hydraulic fluid may cause serious engine failure, and due to the corrosive effect of phosphate esters on cobalt, the level of phosphate ester must not exceed 1 ppm in jet fuel. The jet fuel should be tested for traces of phosphate compounds. This article describes methods for identification and quantification of Exxon and Skydrol hydraulic fluid contamination in jet fuel. Both of the fluids are composed of tri-butyl phosphate. Jet fuel chromatogram peaks interfere with identifying this compound's main peak, thus two techniques to separate the jet fuel peaks from the tri-butyl phosphate peaks were developed. One is based on a solid phase extraction procedure followed by identification and quantification which is carried out using a gas chromatograph equipped with a mass spectrometer or by a gas chromatograph equipped with a flame ionization detector. The other separation technique is single-staged, where the separation and analysis are carried out by a gas chromatograph equipped with a DB-WAX column and MS. Lowest level of detection reached was 0.1 ppm of tri-butyl phosphate in jet fuel; approximately 10 times lower than the limit. Linearity was achieved in all analysis methods up to contamination of 100 ppm.