Exceeding 5000-Fold Concentration of Dilute Analytes in Micellar Electrokinetic Chromatography

Abstract

When a neutral analyte zone is injected into a charged pseudostationary phase, the length of the zone is predicted to be narrowed by 1/(1 + k), where k is the retention factor. The conditions for zone narrowing to occur assume negligible electroosmotic flow, a relatively constant electric field along the capillary column, and no pseudostationary phase in the injected analyte mixture. The theoretically expected concentration enhancement was demonstrated experimentally. Consequently, the detection sensitivity of analytes in micellar electrokinetic chromatography (MEKC) can be improved significantly. For example, 9 to 18 parts per billion of an environmentally important racemic herbicide spiked in lake water was separated by MEKC and detected by ultraviolet absorption.

Comparison of two capillary electrophoresis online stacking modes by analysis of polycyclic aromatic hydrocarbons in airborne particulates

“…Sweeping in MEKC is defined as the accumulation of analytes by the charged micelle that fills or penetrates the sample zone during application of a voltage [18]. The online preconcentration procedures were as follows: The capillary was initially conditioned with micellar buffer solution; then, a long plug of sample diluted with buffer without addition of SDS was introduced at 0.5 psi for 90 s. When 25 kV voltage was applied, PAHs at the front end of the sample plug were trapped by the more slowly moving micelles; hence, the migration velocities of PAHs were reduced.…”

“…The concentration extent is affected by the swept zone length (l sweep ) [18]. The shorter the swept zone length is, the more efficiently the analytes can be focused.…”

“…In the present work, two sample stacking methods were compared. One is the sweeping method [18], which is based on the accumulation of analyte molecules using an additive owning considerable affinity for analytes. The sweeping method requires that the sample matrix is devoid of micelles.…”

Enhanced pH‐mediated stacking of anions for CE incorporating a dynamic pH junction

“…This can be especially detrimental when using photometric detection since the small capillary dimensions already place a limitation on concentration sensitivity. Improving sensitivity for optical detection methods has been the focus of many investigations [1][2][3][4]. The most common method to reverse this effect is to perform a dilution or extraction of the sample into a low-ionic strength matrix in order to increase the field strength in the sample zone relative to the background electrolyte (BGE), and is generally referred to as fieldamplified sample stacking [5][6][7].…”

High‐sensitive protein analysis by FESI‐CE‐MALDI‐MS

“…For example, the acido-basicity or hydrophobicity characteristics of the considered analytes are used in the dynamic pH junction [14][15][16][17] and sweeping [18] [19,20]. It combines the strengths of electrokinetic injection and those of t-ITP and has so far been applied to small ions [21], DNA strands [22], SDS denaturized proteins [23] as well as peptides [24].…”