Surface characterization of 1-butyl-1-ethylpiperidinium bromide by inverse gas chromatography

Abstract This work addresses the surface characterization of an organic salt based on a piperidinium cation and a halide anion, similar to a first generation ionic liquid, using the Inverse Gas Chromatography (IGC) technique. IGC was employed in order to assess the dispersive surface energy and the acid/base character of 1-butyl-1-ethylpiperidinium bromide, [C 2 C 4 PIP]Br at a temperature range (313.15–343.15 K) well below its melting point, where the retention mechanism is governed by the surface adsorption of the probes. This type of characterization was possible due to the high melting point of [C 2 C 4 PIP]Br, namely 413.15 K. The dispersive component of the surface energy was estimated with the aid of the Schultz method and the Dorris-Gray method. Results obtained using the first method were higher than the ones obtained by the latter. The discrepancy between the two methods was found to increase with the increase of temperature. The acid/base characterization was implemented by using the Flour and Papirer approach as well as the Brookman and Sawyer method. The acidity and basicity constants of the surface of [C 2 C 4 PIP]Br revealed that it is amphoteric with a predominantly basic character.