Physical Ionic Liquid/Polysiloxane Mixtures for Tuning the Polarity and the Selectivity of the Polysiloxane Stationary Phase for GC Analysis

Two novel room-temperature ionic liquids (RTILs), a mono-cationic (tetra-n-octylammonium) and a dicationic (bis-methylpiperidinium-butylidene) room-temperature ionic liquid with the bis[(trifluoromethyl)sulfonyl]imide anion, were individually mixed with OV-1701 polysiloxane to tune the selectivity and the polarity of stationary phases for GC. The interaction properties of the stationary phases were investigated on the basis of polarity calculations and the linear solvation energy relationship. The incorporation of the monocationic RTIL in the OV-1701 increased the dipolarity/polarizability capacities (s) and the hydrogen-bond basicity ability (a) allowing the separation of the m-chloroaniline/p-chloroaniline isomers and the m-xylene/p-xylene isomers which are not usually separated on polysiloxane stationary phase. The mixed stationary phases exhibited a greater selectivity than the OV-1701 phase for the majority of the aromatic compounds tested, demonstrating a kind of synergistic effect of the combination of polysiloxane and RTIL. The addition of RTIL proved to be an original method to modulate the polarity and the selectivity of the stationary phase of intermediate polarity in order to prepare stationary phases dedicated for specific separation with good durability (more than 20 months and more than 1,000 injections) and without any loss of thermal stability.