Direct determination of corrosion inhibitor in aviation fuel by a column-switching technique using gel-permeation chromatography

Abstract

Hitec E580 is added to aviation fuel as an antiwear agent and corrosion inhibitor. The normal concentration range is 10-20 ppm and the level may be determined by measuring the concentration of the major active ingredient, namely dimer acid (technical-grade dilinoleic acid). The method of Hillman et al. involves multiple extractions of the dimer acid from a large volume of fuel and measurement is achieved by gel-permeation chromatography (GPC) with refractive index detection. This paper describes an improved method. It uses an on-line precolumn, containing a polar packing, to extract the dimer acid from the fuel. Operation of a switching valve allows the precolumn to be flushed with tetrahydrofuran (THF), thus transferring the dimer acid to a GPC column. Refractive index detection is used. The two methods give results which are in acceptable agreement