title: Study of the mechanism of acetonitrile stacking and its application for directly combining liquid-phase microextraction with micellar electrokinetic chromatography.
abstract: Acetonitrile stacking is an online concentration method that is distinctive due to its inclusion of a high proportion of organic solvent in sample matrices. We previously designed a universal methodology for the combination of liquid-phase microextraction (LPME) and capillary electrophoresis (CE) using acetonitrile stacking and micellar electrokinetic chromatography (MEKC) mode, thereby achieving large-volume injection of the diluted LPME extractant and the online concentration. In this report, the methodology was extended to the analysis of highly substituted hydrophobic chlorophenols in wines using diethyl carbonate as the extractant. Additionally, the mechanism of acetonitrile stacking was studied. The results indicated that the combination of LPME and MEKC exhibited good analytical performance: with ∼40-fold concentration by LPME, a 20-cm (33% of the total length) sample plug injection of an eight-fold dilution of diethyl carbonate with the organic solvent-saline solution produced enrichments higher by a factor of 260-791. Limits of qualification ranged from 5.5 to 16.0ng/mL. Acceptable reproducibilities of lower than 1.8% for migration time and 8.6% for peak areas were obtained. A dual stacking mechanism of acetonitrile stacking was revealed, involving transient isotachophoresis plus pH-junction stacking. The latter was associated with a pH shift induced by the presence of acetonitrile. The pseudo-stationary phase (Brij-35) played an important role in reducing the CE running time by weakening the isotachophoretic migration of the analyte ions following Cl(-) ions. The combination of acetonitrile stacking and nonionic micelle-based MEKC appears to be a perfect match for introducing water-immiscible LPME extractants into an aqueous CE system and can thus significantly expand the application of LPME-CE in green analytical chemistry.
authors.affiliation: College of Science, Northwest A&F University, No. 3 Taicheng Road, Yangling, Shaanxi 712100, China.
authors.forename: Jingru
authors.initials: J
authors.lastname: Sun
authors.affiliation: College of Science, Northwest A&F University, No. 3 Taicheng Road, Yangling, Shaanxi 712100, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Feng
authors.affiliation: College of Science, Northwest A&F University, No. 3 Taicheng Road, Yangling, Shaanxi 712100, China.
authors.forename: Ludi
authors.initials: L
authors.lastname: Shi
authors.affiliation: College of Food Sciences and Engineering, Northwest A&F University, Yangling, China.
authors.forename: Laping
authors.initials: L
authors.lastname: Liu
authors.affiliation: College of Science, Northwest A&F University, No. 3 Taicheng Road, Yangling, Shaanxi 712100, China.
authors.forename: Hui
authors.initials: H
authors.lastname: He
authors.affiliation: College of Science, Northwest A&F University, No. 3 Taicheng Road, Yangling, Shaanxi 712100, China.
authors.forename: Yingying
authors.initials: Y
authors.lastname: Fan
authors.affiliation: College of Natural Resources and Environment, Northwest A&F University, Yangling, China.
authors.forename: Shibin
authors.initials: S
authors.lastname: Hu
authors.affiliation: College of Science, Northwest A&F University, No. 3 Taicheng Road, Yangling, Shaanxi 712100, China. Electronic address: shuhliu@nwsuaf.edu.cn.
authors.forename: Shuhui
authors.initials: S
authors.lastname: Liu
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D002733:Chlorophenols / Q000032:analysis / Q000737:chemistry; D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D019075:Electrophoresis, Capillary / Q000379:methods; D059627:Liquid Phase Microextraction / Q000379:methods*; D011092:Polyethylene Glycols / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014920:Wine / Q000032:analysis
chemical_list: D000097:Acetonitriles; D002733:Chlorophenols; D012997:Solvents; D014867:Water; D011092:Polyethylene Glycols; C515901:Brij 35; C032159:acetonitrile
keywords: Acetonitrile stacking; Chlorophenol; Liquid-phase microextraction; Micellar electrokinetic chromatography