Inverse Gas Chromatography Used to Study Lubricating Oil Oxidation Mechanism via Changes in Kovats and Flory-Huggins Retention Parameters

Inverse gas chromatographic technique(IGC) was attempted as a new approach to follow the chem-ical changes that occur during lubricating base oil oxidation.Three groups of the oxidized base oils were pre-pared at different oxygen flow rates,periods and temperatures according to IP48method.The corrected reten-tion volumes(VR) were calculated for a series of selected test solutes possessing different functional groups onthe oxidized base oils used as stationary phases.Kovats retention index(I),Flory-Huggins interaction parame-ter(κ1∞,2),and partial molar free energy of solution(ΔGL∞),were calculated for the given test solutes fromtheirVR.The relationships between theIvalues and the oxidation variables were plotted and discussed.Theobtained results were confirmed by potentiometric titration.The study reveals that the magnitudes of variationofI,κ1∞,2orΔG∞Lretention parameters depend on the oxidation degree of the base oil.Large differences be-tween theIvalues permit discrimination between the different oxidation steps.Key words: inverse gas chromatography(IGC);oxidation;lubricating base oil;Kovats retention

Inverse gas chromatographic technique （ IGC ） was attempted as a new approach to follow the chemical changes that occur during lubricating base oil oxidation. Three groups of the oxidized base oils were prepared at different oxygen flow rates, periods and temperatures according to IP48 method. The corrected retention volumes （ VR ） were calculated for a series of selected test solutes possessing different functional groups on the oxidized base oils used as stationary phases. Kovats retention index （Ⅰ）, Flory-Huggins interaction parameter （ K^∞ 1,2 ）, and partial molar free energy of solution （ △GL^∞ ）, were calculated for the given test solutes from their VR. The relationships between the Ⅰ values and the oxidation variables were plotted and discussed. The obtained results were confirmed by potentiometric titration. The study reveals that the magnitudes of variation of Ⅰ, K^∞ 1,2 or △GL^∞ retention parameters depend on the oxidation degree of the base oil. Large differences between the Ⅰ values permit discrimination between the different oxidation steps.