Sweeping of alprenolol enantiomers with an organic solvent and sulfated ß-cyclodextrin in capillary electrophoresis.

Sweeping, an on-line sample concentration technique in CE, is the picking and accumulation of analytes by the pseudostationary phase or complexing additive. In the presence of an electric field, the analytes concentrated at the additive front that initially penetrated the sample zone. Here, we describe the sweeping of cationic alprenolol enantiomers using sulfated ß-CD and organic solvent. The separation solution contained the anionic additive while ACN was in the sample solution. With fused silica capillaries, positive polarity, and solutions buffered at pH 3, the direction of the enantiomers' effective electrophoretic mobility was the same as the electrophoretic mobility (or electrophoretic mobility without additive). When the amount of ACN in the sample was increased (i.e. 60%), the interaction between the analytes and additive became negligible. This caused the sweeping boundary to shift from the electrophoretically moving ß-CD front to the zone between the sample and separation solution. The equation that described the narrowing of injected sample zone was derived. The performance of sweeping with 60% ACN in the sample was then studied under different operating conditions (e.g. type of injection, injection time, and CD concentration). The low interaction between enantiomers and additive gave only moderate increases in sensitivity (approximately tenfold), but was improved when field enhancement was used during electrokinetic injection. With a conductivity difference (separation/sample solution) of 70 and a short injection time of 30 s at 20 kV, peak improvements of >100-fold was easily achieved.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010-2012).

CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.

Synergistic effect of field enhanced sample injection on micelle to solvent stacking in capillary electrophoresis.

Injection of a sodium dodecyl sulfate micellar plug prior to the sample solution induced transient micellar phase extraction of cationic drugs in capillary electrophoresis. Micelle to solvent stacking mechanism was utilized by preparing the sample in aqueous organic solvent. Synergism was achieved with field enhanced sample injection that allowed larger sample loads. Micelle to solvent stacking occurred concurrently with the enhanced injection after the fast moving analytes electrophoretically migrated into the micellar plug. This was different from stacking combinations with field enhancement where the electric field strength difference was involved in analyte focusing. Using a sample diluent that had one-tenth the conductivity of the background solution, the strategy afforded thousands-fold improvements in peak height and LODs (S/N=3) of as low as 1.1 ng/mL. The results were repeatable and linear. Adaptability to real sample analysis was evaluated using spiked urine sample after minimal sample clean-up.

Capillary electrophoresis of natural products: highlights of the last five years (2006-2010).

An extensive search of the published research and review articles indicated a growing number of works that employed electroseparation techniques. Capillary zone electrophoresis (CZE) and electrokinetic chromatography (EKC), in particular, were found to be popular for the analyses of natural products. This review outlines the important developments in this field over the years, especially during the 2006-2010 period. An overview of the natural product applications such as pharmaceuticals/herbal products, fingerprinting and quality control, food and food contaminants, and toxicological compounds of interest to forensics were presented. Important areas of detection strategies, microchips, sample preconcentration, and chiral separations were also discussed. Hence, quick information was provided on the researches already undertaken and the possibilities of unexplored areas. In addition, fundamental concepts for the understanding of CZE and EKC and their suitability for natural products analyses were briefly discussed.