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Neutral Analytes (neutral + analyte)
Selected AbstractsDirect on-line analysis of neutral analytes by dual sweeping via complexation and organic solvent field enhancement in nonionic MEKCELECTROPHORESIS, Issue 8 2009Jun Cao Abstract Conventionally, neutral compounds cannot be separated by nonionic micelle capillary electrophoresis. In this report, the development of a novel on-line preconcentration technique combining dual sweeping based on complexation and organic solvent field enhancement is applied to the sensitive and selective analysis of three neutral glucosides: ginsenoside Rf, ginsenoside Rg1, and ginsenoside Re. Nonionic micelle detectability by CE is demonstrated through effective focusing of large sample volumes (up to 38% capillary length) using a dual sweeping mode. This results in a 50- to 130-fold improvement in the LODs relative to conventional injection method. Neutral compounds sweeping is examined in terms of analyte mobility dependence on borate complexation, solvent viscosity difference, and Brij-35 interaction. Enhanced focusing performance by this hyphenated method was demonstrated by a greater than fourfold reduction in glucoside bandwidth, as compared with common sweeping (devoid of organic solvent-mediated sweeping method in the sample matrices). Moreover, separation efficiencies greater than a million theoretical plates can be achieved by sweeping large sample volumes into narrow zones. The designated method was also tested for its ability to determine the presence of glucosides in the crude extracts obtained from plant sample. [source] Methacrylate-based monolithic column with mixed-mode hydrophilic interaction/strong cation-exchange stationary phase for capillary liquid chromatography and pressure-assisted CECELECTROPHORESIS, Issue 19 2008Jian Lin Abstract A novel porous polymethacrylate-based monolithic column by in situ copolymerization of 3-sulfopropyl methacrylate (SPMA) and pentaerythritol triacrylate in a binary porogenic solvent consisting of cyclohexanol/ethylene glycol was prepared. The monolith possessed in their structures bonded sulfonate groups and hydroxyl groups and was evaluated as a hydrophilic interaction and strong cation-exchange stationary phases in capillary liquid chromatography (cLC) and pressure-assisted CEC using small polar neutral and charged solutes. While the SPMA was introduced as multifunctional monomer, the pentaerythritol triacrylate was used to replace ethylene glycol dimethacrylate as cross-linker with much more hydrophilicity due to a hydroxyl sub-layer. The different characterization of monolithic stationary phases were specially designed and easily prepared by altering the amount of SPMA in the polymerization solution as well as the composition of the porogenic solvent for cLC and pressure-assisted CEC. The resulting monolith showed the different trends about the effect of the permeabilities on efficiency in the pressure-assisted CEC and cLC modes. A typical hydrophilic interaction chromatography mechanism was observed at higher organic solvent content (ACN%>70%) for polar neutral analytes. For polar charged analytes, both hydrophilic interaction and electrostatic interaction contributed to their retention. Therefore, for charged analytes, selectivity can be readily manipulated by changing the composition of the mobile phase (e.g., pH, ionic strength and organic modifier). With the optimized monolithic column, high plate counts reaching greater than 170,000,plates/m for pressure-assisted CEC and 105,000 plates/m for cLC were easily obtained, respectively. [source] Capillary electrochromatography with zwitterionic stationary phase on the lysine-bonded poly(glycidyl methacrylate- co -ethylene dimethacrylate) monolithic capillary columnELECTROPHORESIS, Issue 12 2006Xiaoli Dong Abstract A polymer-based neutral monolithic capillary column was prepared by radical polymerization of glycidyl methacrylate and ethylene dimethacrylate in a 100,,m id fused-silica capillary, and the prepared monolithic column was subsequently modified based on a ring opening reaction of epoxide groups with 1,M,lysine in solution (pH,8.0) at 75°C for 10,h to produce a lysine chemically bonded stationary phases in capillary column. The ring opening reaction conditions were optimized so that the column could generate substantial EOF. Due to the zwitterionic functional groups of the lysine covalently bonded on the polymer monolithic rod, the prepared column can generate cathodic and anodic EOF by varying the pH values of running buffer during CEC separation. EOF reached the maximum of ,2.0×10,8,m2v,1s,1 and 2.6×10,8,m2v,1s,1 with pH of the running buffer of 2.25 and 10, respectively. As a consequence, neutral compounds, ionic solutes such as phenols, aromatic acids, anilines, and basic pharmaceuticals were all successfully separated on the column by CEC. Hydrophobic interaction is responsible for separation of neutral analytes. In addition, the electrostatic and hydrophobic interaction and the electrophoretic migration play a significant role in separation of the ionic or ionizable analytes. [source] Simultaneous separation of fifteen approved protease and reverse transcriptase inhibitors for human immunodeficiency virus therapy by capillary electrophoresisELECTROPHORESIS, Issue 4 2003Nguyen Duc Tuan Abstract In the present investigation, a novel approach towards a complete separation of all 15 protease and reverse transcriptase inhibitors which are currently approved for use in highly active antiretroviral therapy in a single analytical run is presented. The developed method employs an acidic background electrolyte with sodium polyanethol sulfonate (SPAS) as polyanionic electroosmotic flow (EOF) modifier to establish a strong cathodic EOF, sodium dodecyl sulfate (SDS) as pseudostationary selector, and acetonitrile and ethanol as organic modifiers. Separation of the analytes is based on two different mechanisms. The more basic analytes are protonated at the prevailing pH conditions and thus migrate in front of the cathodic EOF, whereas the less basic and neutral analytes interact with the SDS and are retained after the EOF. By optimizing electrolyte pH, the amount of solvents and SDS concentrations in the background electrolyte it is possible to completely separate all compounds of interest. [source] Online preconcentration using monoliths in electrochromatography capillary format and microchipsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2007Violaine Augustin Abstract Online preconcentration and separation of analytes using an in situ photopolymerized hexyl acrylate-based monolith stationary phase was evaluated using electrochromatography in capillary format and microchip. The band broadening occurring during the preconcentration process by frontal electrochromatography and during the desorption process by elution electrochromatography was studied. The hexyl acrylate-based monolith provides high retention for neutral analytes allowing the handling of large sample volumes and its structure allows rapid mass transfer, thus reducing the band broadening. For moderately polar analytes such as mono-chlorophenols that are slightly retained in water, it was shown that enrichment factors up to 3500 can be obtained by a hydrodynamic injection of several bed volumes for 120 min under 0.8 MPa with a decrease in efficiency of 50% and a decrease of 30% for the resolution between 2- and 3-chlorophenol. An 8 min preconcentration time allows enrichment factors above 100 for polyaromatic hydrocarbons. The interest of these monoliths when synthesized in microchip is also demonstrated. A 200-fold enrichment was easily obtained for PAHs with only 1 min as preconcentration time, without decrease in efficiency. [source] Phospholipids in liquid chromatography/mass spectrometry bioanalysis: comparison of three tandem mass spectrometric techniques for monitoring plasma phospholipids, the effect of mobile phase composition on phospholipids elution and the association of phospholipids with matrix effectsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2009Yuan-Qing Xia Because plasma phospholipids may cause matrix effects in bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods, it is important to establish optimal mass spectrometric techniques to monitor the fate of phospholipids during method development and application. We evaluated three MS/MS techniques to monitor phospholipids using positive and negative electrospray ionization (ESI). The first technique is based on using positive precursor ion scan of m/z 184, positive neutral loss scan of 141 Da and negative precursor ion scan of m/z 153. The second technique is based on using class-specific positive and negative selected reaction monitoring (SRM) transitions to monitor class-representative phospholipids. The third technique, previously reported, utilizes in-source collision-induced dissociation (CID)-based positive SRM of m/z 184,,,184. We recommend the all-inclusive technique 1 for use in qualitative assessment of all classes of phospholipids and technique 2 for use in quantitative assessment of class-representative phospholipids. Secondly, we evaluated the elution behaviors of the plasma phospholipids under different reversed-phase mobile phase conditions. The phospholipid-eluting strength of a mobile phase was mainly dependent on the type and amount (%) of the organic eluent and the strength increased in the order of methanol, acetonitrile and isopropyl alcohol. Under the commonly used gradient and isocratic elution schemes in LC/MS/MS bioanalysis, not all the phospholipids are eluted off the column. Thirdly, we investigated the association between phospholipids and matrix effects in positive and negative ESI using basic, acidic and neutral analytes. While the phospholipids caused matrix effects in both positive and negative ESI, the extent of ionization suppression was analyte-dependent and was inversely related to the retention factor and broadness of the phospholipids peaks. The lysophospholipids which normally elute earlier in reversed-phase chromatography are more likely to cause matrix effects compared to the later-eluting phospholipids in spite of the larger concentrations of the latter in plasma. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||