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Determination of trace cationic impurities in butylmethylimidazolium‐based ionic liquids: From transient to comprehensive single‐capillary counterflow isotachophoresis‐zone electrophoresis
Author(s) -
Urbánek Marek,
Varenne Anne,
Gebauer Petr,
Křivánková Ludmila,
Gareil Pierre
Publication year - 2006
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200600316
Subject(s) - isotachophoresis , capillary electrophoresis , chemistry , electrolyte , chromatography , capillary action , impurity , acetic acid , ammonium acetate , analytical chemistry (journal) , high performance liquid chromatography , materials science , electrode , composite material , biochemistry , organic chemistry
Determination of impurities in ionic liquids (ILs) remains a difficult task. In this work, the hyphenation of isotachophoretic (ITP) preconcentration to zone electrophoresis (ZE) has been explored for the trace analysis of the cationic impurities Na + , Li + , and methylimidazolium (MI + ) in butylmethylimidazolium (BMI + )‐based ILs. Simultaneous detection of UV‐transparent and UV‐absorbing impurities was ensured by a BGE composed of creatinine‐acetate buffer. To induce ITP, three different strategies were evaluated: (i) Sample self‐stacking ensured by the addition of ammonium acetate (NH 4 Ac) to 25–50‐fold diluted IL solution (transient ITP). (ii) Complete ITP‐ZE separation performed in a single capillary: ITP was realized in discontinuous electrolytes comprising an 80 mM NH 4 Ac, 40 mM acetic acid, 30 mM α‐CD, pH 5.05, leading electrolyte (LE) and a 10 mM creatinine, 10 mM acetic acid, pH 4.9, terminating electrolyte (TE). To create the ZE stage, the ITP stack of analytes was moved back toward the capillary inlet by pressure and simultaneously the capillary was filled with the BGE. This protocol made it possible to accommodate a 2.5‐times diluted IL sample. (iii) Complete counterflow ITP‐ZE with continuous electrokinetic sample supply: the ITP stage was performed in a capillary filled with a 150 mM NH 4 Ac, 75 mM acetic acid, 30 mM α‐CD, pH 5.0 LE, with 40‐times diluted IL at the capillary inlet. BMI + from IL acts as the terminating ion. The LODs reached in this latter case were at the 10 and 1 ppb levels for MI + and Li + in diluted IL matrix, respectively.