Stacking and Separation of Neutral and Cationic Analytes in Interface-Free Two-Dimensional Heart-Cutting Capillary Electrophoresis

Abstract

Interface-free two-dimensional heart-cutting capillary electrophoresis is typically used to purify/concentrate and separate a single target fraction. Here, we demonstrate the simultaneous stacking and orthogonal separation of target fractions that belong to two different classes of compounds. The cationic species were first analyzed by capillary zone electrophoresis using an electrolyte of low pH in a fused-silica capillary. The neutrals that remained inside the capillary after the first dimension analysis were then separated by micellar electrokinetic chromatography using sodium dodecyl sulfate micelles that were electrophoretically introduced into the capillary. The suppression of electro-osmotic flow using low pH was essential in shifting the separation selectivity from electrophoresis to electrokinetic chromatography. Two approaches to stacking based on the solubility of the species present were developed. Stacking was achieved during the first dimension analysis via sweeping and/or analyte focusing by micelle collapse. Two artificial mixtures (eight cationic drugs/five neutral steroids, and three quaternary ammonium/three neutral organophosphate pesticides) were successfully analyzed with sensitivity enhancement factors from 15 to 100. Some analytical parameters and application to a spiked real water sample were also studied.

Recent advances in microscale separation

“…Kukusamude et al. demonstrated the simultaneous stacking and orthogonal separation of target fractions that belong to two different classes of compounds by CZE coupling to MEKC. Neutral and cationic analytes were successfully analyzed with sensitivity enhancement factors from 15 to 100.…”

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2014–2016)

“…In AFMC [95,[105][106][107][108][109], the analytes were neutral UV absorbents [107,109], cationic herbicides [108], neutral pesticides [108], drugs [95], vitamins [106], neurotoxin [105], amino acid [105], and sugar [105]. The samples were sunscreen, river water, human blood and urine, and food products.…”

“…The samples were sunscreen, river water, human blood and urine, and food products. The sample preparations included LLE [107,109], drying and reconstitution [108], protein precipitation [95,106], and ultrasound-assisted extraction [105]. The pseudo-phase was typically SDS at concentration of 5-7.5 mM [107-109] or 1-butyl-3-methylimidazolium bromide at a concentration of 3 M [95, 105,106] as the micelle forming agent in the sample.…”

Contemporary sample stacking in analytical electrophoresis

“…Kukusamude et al. demonstrated the possibilities of the use of interface‐free 2D heart‐cutting CE for simultaneous stacking and orthogonal separation of two groups of analytes of substantially different properties. This was reached by performing the analysis in two subsequent stages differing by the BGE used.…”