Dual-opposite injection electrokinetic chromatography for the unbiased, simultaneous separation of cationic and anionic compounds

Abstract

The concept of dual opposite injection in capillary electrophoresis (DOI-CE) for the simultaneous separation, under conditions of suppressed electroosmotic flow, of anionic and cationic compounds with no bias in resolution and analysis time, is extended to a higher pH range in a zone electrophoresis mode (DOI-CZE). A new DOI-CE separation mode based on electrokinetic chromatography is also introduced (DOI-EKC). Whereas conventional CZE and DOI-CZE are limited to the separation of charged compounds with different electrophoretic mobilities, DOI-EKC is shown to be capable of separating compounds with the same or similar electrophoretic mobilities. In contrast to conventional EKC with charged pseudostationary phases that often interact too strongly with analytes of opposite charge, the neutral pseudostationary phases appropriate for DOI-EKC are simultaneously compatible with anionic and cationic compounds. This work describes two buffer additives that dynamically suppress electroosmotic flow (EOF) at a higher pH (6.5) than in a previous study (4.4), thus allowing DOI-CZE of several pharmaceutical bases and weakly acidic positional isomers. Several DOI-EKC systems based on nonionic (10 lauryl ether, Brij 35) or zwitterionic (SB-12, CAS U) micelles, or nonionic vesicles (Brij 30) are examined using a six-component test mixture that is difficult to separate by CZE or DOI-CZE. The effect of electromigration dispersion on peak shape and efficiency, and the effect of surfactant concentration on retention, selectivity, and efficiency are described.

Towards dynamic coating of glass microchip chambers for amplifying DNAvia the polymerase chain reaction

“…In addition, two other agents were tested: HEC and EPDMA. HEC was worthy of exploration as a result of its being reported to dynamically coat capillaries for protein separations [20,21] while EPDMA was tested due to its ability to generate a robust adsorbed coating that prevents protein and DNA adsorption [22,23].…”

“…In addition, HEC has been used effectively for preventing adsorption of proteins onto the capillary wall [21]. Consequently, HEC was evaluated for its utility as a dynamic or adsorbed coating.…”

Weak Binding of N-Alkylpyridinium Ions to Nonionic Surfactant Micelles as Studied by Capillary Zone Electrophoresis

“…The result is attributed to the suppressed speed of the EOF; polyether-type nonionic surfactants adsorb onto the capillary wall and suppress the electroosmotic flow. 24,25 Electrophoretic mobility of the alkylpyridinium ions, μep ′ , was measured in the absence and presence of the surfactant micelle; those with Brij 58 are shown in Fig. 2.…”

Simultaneous determination of inorganic and organic anions, alkali, alkaline earth and transition metal cations by capillary electrophoresis with contactless conductometric detection

“…The sample may or may not be injected into both capillary ends at the same time; by delaying the injection of the second sample portion, the separation selectivity can be modified. Dual opposite end injection is not limited to the analysis of small, highly charged ions [10][11][12][13][14] but can as well be applied for the separation of large molecules [15].…”