Zhao Qichao, Eichhorn Jens, Pitner William R, Anderson Jared L
Department of Chemistry, The University of Toledo, 2801 W. Bancroft Street, MS 602, Toledo, OH 43606, USA.
Anal Bioanal Chem. 2009 Sep;395(1):225-34. doi: 10.1007/s00216-009-2951-1. Epub 2009 Jul 24.
Ionic liquids (ILs) containing the tris(pentafluoroethyl)trifluorophosphate anion [FAP]- have attracted increased attention due to their unique properties including ultrahigh hydrophobicity, hydrolytic stability, and wide electrochemical window. In this study, the solvation parameter model is used via gas chromatography to characterize the solvation interactions of seven ILs containing amino, ester, and hydroxyl functional groups appended to the cation and paired with [FAP]-, as well as three ILs containing the bis[(trifluoromethyl)sulfonyl]imide anion [NTf2]-. The role of the functional groups, nature of the counter anion, and cation type on the system constants were evaluated. ILs containing [FAP]- possessed lower hydrogen bond basicity than NTf2-based ILs having the same cationic component; in the case of hydroxyl-functionalized cations, the presence of [FAP]- led to an enhancement of the hydrogen bond acidity, relative to the NTf2-analogs. The system constants support the argument that [FAP]- weakly coordinates the cation and any appended functional groups, promoting properties of the cation which might be masked by stronger interactions with other anion systems. The chromatographic performance of the IL stationary phases was evaluated by examining the retention behavior and separation selectivity for chosen analytes. The results from this work can be used as a guide for choosing FAP-based ILs capable of exhibiting desired solvation properties while retaining important physical properties including high thermal stability and high hydrophobicity.
含有三（五氟乙基）三氟磷酸根阴离子[FAP]⁻的离子液体（ILs）因其独特的性质，包括超高疏水性、水解稳定性和宽电化学窗口，而受到越来越多的关注。在本研究中，通过气相色谱法使用溶剂化参数模型来表征七种阳离子上带有氨基、酯基和羟基官能团并与[FAP]⁻配对的离子液体以及三种含有双[（三氟甲基）磺酰基]亚胺阴离子[NTf₂]⁻的离子液体的溶剂化相互作用。评估了官能团、抗衡阴离子的性质和阳离子类型对体系常数的影响。含有[FAP]⁻的离子液体比具有相同阳离子成分的基于NTf₂的离子液体具有更低的氢键碱度；在羟基官能化阳离子的情况下，相对于NTf₂类似物，[FAP]⁻的存在导致氢键酸度增强。体系常数支持这样的观点，即[FAP]⁻与阳离子和任何附加的官能团弱配位，促进阳离子的性质，而这些性质可能会被与其他阴离子体系的更强相互作用所掩盖。通过检查所选分析物的保留行为和分离选择性来评估离子液体固定相的色谱性能。这项工作的结果可作为选择基于FAP的离子液体的指南，这些离子液体能够展现所需的溶剂化性质，同时保留包括高热稳定性和高疏水性在内的重要物理性质。
