1-Butyl-3-methylimidazolium-based ionic liquids and an anionic surfactant: Excellent background electrolyte modifiers for the analysis of benzodiazepines through capillary electrophoresis

• Published in: Journal of Chromatography A Vol. 1217; no. 17; pp. 2973 - 2979
• Main Authors: Su, Hsiu-Li, Kao, Wan-Chun, Lin, Kuan-Wen, Lee, Cheng-yu, Hsieh, You-Zung
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 23.04.2010; Amsterdam; New York: Elsevier; Elsevier
• Subjects: 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; Analysis; Benzodiazepine; Benzodiazepines - chemistry; Benzodiazepines - isolation & purification; Biological and medical sciences; Capillary electrophoresis; Electrophoresis, Capillary - instrumentation; Electrophoresis, Capillary - methods; General pharmacology; Humans; Imidazoles - chemistry; Ionic liquids; Ionic Liquids - chemistry; Medical sciences; Pharmacology. Drug treatments; Surface-Active Agents - chemistry; Urine - chemistry; Ionic liquids; 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; Capillary electrophoresis; Benzodiazepine; Human; Urine; Solid phase extraction; Biological fluid; Chemical analysis; Psychotropic; Micellar electrokinetic capillary chromatography; Hypnotic; Chemical enrichment; Ionic liquid; Anionic surfactant; Ultraviolet detector; Sample preparation; Tranquillizer; Benzodiazepine derivatives; Lorazepam; Sedative; Quantitative analysis
• ISSN: 0021-9673; 1873-3778
• DOI: 10.1016/j.chroma.2010.02.056

In this study, we found that adding 1-butyl-3-methylimidazolium-based ionic liquids (ILs) and sodium dodecyl sulfate (SDS) as modifiers in the background electrolyte (BGE) for capillary electrophoresis enhanced the separation of benzodiazepines. In particular, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf 2]) was the best IL additive for the separation system because its anionic moiety interacted favorably with the benzodiazepines. We added SDS because of its known effect on the separation of hydrophobic analytes. We optimized the separation conditions in terms of the concentrations of the IL, SDS, and organic solvent, the pH, and the BGE's ionic strength. The optimal BGE, containing 170 mM [BMIM][NTf 2] and 10 mM SDS, provided baseline separation, high efficiency, and satisfactory peak shapes for the benzodiazepines. The separation mechanism was based on heteroassociation between the anionic moiety of the IL and the benzodiazepines, with SDS improving the resolution of the separation. The limits of detection for the seven analytes ranged from 2.74 to 4.42 μg/mL. We subjected a urine sample to off-line solid phase extraction (SPE) prior to the analysis of its benzodiazepine content. Our experimental results reveal that the combination of [BMIM][NTf 2] and SDS provides adequate separation efficiency for its application to CE analyses of benzodiazepines after SPE concentration.