Fullerene-impregnated ionic liquid stationary phases for gas chromatography

Abstract

A new method has been developed to facilitate the use of fullerenes as stationary phases (SPs) in gas chromatography (GC). In this method, ionic liquids (ILs) are used as solvents to coat fullerenes (C₆₀, amino-C₆₀ and hydroxy-C₆₀) onto GC columns. However, the ILs serve not just as coating solvents but also act synergistically with fullerenes to provide unique properties as stationary phases, namely dual modal characteristics. They act as non-polar SPs when separating non-polar analytes (aromatic hydrocarbon mixtures and alkane mixtures), and as polar SPs for polar analytes (e.g., alcohol mixtures). The polarity of the stationary phase can be adjusted by changing either the type of the IL and/or by adding either C₆₀ (or its amino or hydroxy derivatives) to the IL. It was found that C₆₀ and its derivatives produce not only a change in the polarity of the SP but also substantial enhancement in separation efficiencies for both non-polar and polar analytes. More importantly, when added to the IL SP, C₆₀ improves separation efficiencies not just for non-polar analytes (aromatic hydrocarbon mixtures and alkane mixtures) but also for polar analytes (mixtures of ortho-, meta- and para-xylene and alcohol mixtures) as well. Moreover, C₆₀SP provides higher efficiencies than amino-C₆₀ and hydroxy-C₆₀ for separation of polar analytes. This is rather surprising considering that not only are amino-C₆₀ and hydroxy-C₆₀ more polar than C₆₀, but that the IL used to coat the amino- and hydroxy-C₆₀ (i.e., N-ethylpyridinium trifluoroacetate, [EtPy⁺ CF₃COO⁻]) is more polar than the IL used to coat the C₆₀ (i.e., octylmethylimidazolium bis(trifluoromethyl)sulfonyl)amide], [OMIm⁺ (CF₃SO₂)₂N⁻]). Moreover, compared to its amino and hydroxy derivatives, the concentration of C₆₀ in the column was 10 times lower.