Identification and Quantification of Hydraulic Fluid Contamination in Jet Fuel

Konstantin Tartakovsky, Israeli Air Force, Depot 22, Materials Department, Tel Nof, Israel
Diana Gertopski Stamker, Israeli Air Force, Depot 22, Materials Department, Tel Nof, Israel
Abby Soussan, Israeli Air Force, Depot 22, Materials Department, Tel Nof, Israel
Moshe Rabaev, Israeli Air Force, Depot 22, Materials Department, Tel Nof, Israel


Hydraulic fluids (oils) used in aviation hydraulic systems contain a variety of compounds based on phosphate esters. Phosphate ester compounds play a significant role in fire resistance but may also cause corrosion of metals and swelling of polymer seals. Contamination of jet fuel with hydraulic fluid may endanger operating seals and engine parts, which are made of materials that are incompatible with phosphate compounds. The contamination mentioned above may cause serious engine failure. Due to the corrosive effect of phosphate esters on cobalt, the level of phosphate ester contamination must not exceed 1 ppm of hydraulic fluid in engines manufactured using cobalt-containing metals, and must be less than 10 ppm in engines not manufactured using cobalt metals.

Israeli Air Force (IAF) uses hydraulic fluid from two different manufacturers. The first of them has been quantified and identified according to its di-butyl phenyl phosphate component, which does not exist in the second oil. The use of hydraulic fluid mixtures in IAF has revealed a need for a universal method for identification and quantification of both hydraulic fluids in jet fuel.

Identification and quantification of both hydraulic fluids can be carried out based on a tri-butyl phosphate compound that exists in both hydraulic fluids. Characterization of the tri-butyl phosphate compound by GC-MS required separation of the signal 99 m/z originated in the matrix of hydrocarbon peaks in the fuel from the signal originated in the main compound in both oils.

The preparation of the samples by the use of solid phase extraction columns (SPE) was successful in separating the compound from the general fuel fraction. Identification and quantification were carried out using two techniques: in the first, a gas chromatograph was equipped with a mass spectrometer (GC-MS), and in the second, a gas chromatograph was equipped with a flame ionization detector (GC-FID).