Nonmolecular solvents in separation methods: Dual nature of room temperature ionic liquids
Nonmolecular solvents in separation methods: Dual nature of room temperature ionic liquids
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DOI：
10.1021/ac050304
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发表时间：
2005-07-01
影响因子：
7.4
通讯作者：
Huguet, S
中科院分区：
文献类型：
--
作者：
Berthod, A;Ruiz-Angel, MJ;Huguet, S
室温离子液体（RTIL）是一种熔融盐，由于其极低的蒸气压和热稳定性，开始被用作分离方法中的非分子溶剂。RTIL由与阳离子缔合的阴离子形成。这种内在的结构使它们具有双重性。当用作RPLC移动的相中的添加剂以增强碱性化合物分离时，RTIL失去其特定的物理化学性质而仅变成盐。然而，给定的RTIL不等同于用相同阳离子制成的另一种RTIL。它示出的阴离子和阳离子有助于溶质保留和峰效率延伸超出简单的“盐析”或离子配对效应。使用具有不同烷基链长度和氯离子或BF 4-或PF 6-阴离子的九种不同烷基甲基-咪唑鎓离子液体作为添加剂（50 mM最大值）。浓度）在Kromasil C-18柱上对某些阳离子碱性溶质进行液相色谱分离。它表明，与钠盐和乙腈-水30/70 v/v的移动的流动相，阴离子可以吸附在固定相表面根据其溶致性。它们也可以与阳离子碱性溶质形成离子对。烷基-咪唑鎓阳离子也吸附在C18键合固定相上，这是由于其烷基链长度决定的疏水特性。当阳离子吸附降低阳离子溶质保留因子时，阴离子吸附显著增加阳离子溶质保留因子。阳离子吸附是峰形和效率提高的主要原因。RTIL是增强碱性阳离子溶质峰形改变峰位置的添加剂。阴离子溶致性与咪唑鎓阳离子疏水性的适当组合的明智选择允许发挥溶质选择性和分析持续时间。
Room temperature ionic liquids (RTIL) are molten salts starting to be used as nonmolecular solvents in separation methods mainly for their extremely low vapor pressure and thermal stability. RTILs are formed by an anion associated to a cation. This intrinsic structure gives them a dual nature. When used as additives in RPLC mobile phases to enhance basic compound separation, RTILs lose their particular physicochemical properties to become just salts. However, a given RTIL is not equivalent to another one made with the same cation. It is shown that both the anion and the cation contribute to solute retention and peak efficiency extending beyond simple "salting-out" or ion-pairing effects. Nine different alkylmethyl-imidazolium ionic liquids with different alkyl chain length and chloride or BF4- or PF6- anions were used as additives (50 mM max. conc.) in the liquid chromatography separation of some cationic basic solutes on a Kromasil C-18 column. It is shown with sodium salts and an acetonitrile-water 30/70 v/v mobile phase that anions can adsorb on the stationary phase surface according to their lyotropic character. They can also form ion pairs with the cationic basic solutes. Alkyl-imidazolium cations also adsorb on the C18 bonded stationary phase due to hydrophobic character depending on their alkyl chain length. Anion adsorption dramatically increases the cationic solute retention factors when cation adsorption decreases them. The cation adsorption is mainly responsible for peak shape and efficiency enhancements. RTILs are additives that enhance the basic cationic solute peak shape changing peak position. A wise choice of the appropriate combination of anion lyotropy with imidazolium cation hydrophobicity allows playing with solute selectivity and analysis duration.