Exploring Gradients in Electrophoretic Separation and Preconcentration on Miniaturized Devices

Transverse migration and microfluidic concentration of DNA using Newtonian buffers

We present experimental evidence that DNA can be concentrated due to an electrohydrodynamic coupling between a pressure-driven flow and a parallel electric field. The effects of buffer properties on the process were measured in a microfluidic channel. The concentration rates and the efficiency of trapping DNA were quantified as functions of the ion and polymer concentrations of the buffer solution. Buffers with large ion concentrations hindered the ability to trap DNA, reducing the short-time efficiency of the concentration process from nearly 100% to zero. Importantly, DNA was trapped in the microfluidic channel even when the buffer solution lacked any measurable viscoelastic response. These observations indicate that electrohydrodynamic migration drives the concentration of DNA. We found no evidence of viscoelastic migration in these experiments.

Recent progress of sample stacking in capillary electrophoresis (2016-2018)

Electrophoretic sample stacking comprises a group of capillary electrophoretic techniques where trace analytes from the sample are concentrated into a short zone (stack). This paper is a continuation of our previous reviews on the topic and brings a survey of more than 120 papers published approximately since the second quarter of 2016 till the first quarter of 2018. It is organized according to the particular stacking principles and includes chapters on concentration adjustment (Kohlrausch) stacking, on stacking techniques based on pH changes, on stacking in electrokinetic chromatography and on other stacking techniques. Where available, explicit information is given about the procedure, electrolyte(s) used, detector employed and sensitivity reached. Not reviewed are papers on transient isotachophoresis which are covered by another review in this issue.

Recent developments in capillary and microchip electroseparations of peptides (2015-mid 2017)

The review brings a comprehensive overview of recent developments and applications of high performance capillary and microchip electroseparation methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) to analysis, microscale isolation, purification, and physicochemical and biochemical characterization of peptides in the years 2015, 2016, and ca. up to the middle of 2017. Advances in the investigation of electromigration properties of peptides and in the methodology of their analysis (sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, and detection) are described. New developments in particular CE and CEC methods are presented and several types of their applications to peptide analysis are reported: qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC methods to provide important physicochemical characteristics of peptides are demonstrated.