Dual‐opposite‐injection CZE: Theoretical aspects and application to organic and pharmaceutical compounds

Abstract

Several important figures of merit (migration time, efficiency, resolution, resolution per unit time, and electrophoretic selectivity) are quantitatively compared for the first time for conventional CZE and dual-opposite-injection CZE (DOI-CZE). Aspects of DOI-CZE relevant to the separation of organic and pharmaceutical ions (MW>120 Da) are also discussed. Two new approaches to resolve the codetection of anions and cations, hydrodynamic flow-modified DOI-CZE and polarity reversal in combination with asymmetric detector window positioning, are compared with the method of preliminary transport, a variable procedure within sequential sample introduction, using a six-component sample of organic and pharmaceutical compounds. The advantages of DOI-CZE for the simultaneous analysis of organic/pharmaceutical anions and cations are illustrated in a direct comparison of conventional CZE and DOI-CZE for the separation of a ten-component mixture of pharmaceutical ions (five ionized acids and five ionized bases).

Determination of propranolol and hydrochlorothiazide by batch injection analysis with amperometric detection and capillary electrophoresis with capacitively coupled contactless conductivity detection

“…35 If normal EOF was used, cations were separated in co-EOF mode and anions with low mobility in counter-EOF mode (carried to the detector by the EOF). Simulations carried out using CurTiPot soware 36 have indicated that in solutions with pH around 8.7, the mean charge of PROP species is positive (10% neutral and 90% with one positive charge) and that of HCT species is negative (13% neutral; 67% with one negative charge and 20% with two negative charges).…”

Dual‐opposite injection capillary electrophoresis: Principles and misconceptions

“…From the CE separation, the electroosmotic mobility and net mobilities of the analytes can be measured, and from those parameters the electrophoretic mobilities of the analytes can then be calculated. A relatively simple, quantitative approach to completely avoid co‐detection between oppositely charged ionic species in DOI‐CE while simultaneously achieving baseline resolution of all ions using a commercial instrument is summarized below: The electrophoretic mobilities of the fastest and slowest anions and cations under CZE conditions and the EOF under DOI‐CE conditions (or at minimum, a close approximation) must be determined. The minimum migration distance needed for baseline resolution of all anions should be calculated, and then repeated for all cations. If the calculated minimum migration distance for cations or anions (whichever one is selected) is greater than the standard minimum (short‐end) migration distance dictated by the cartridge design of the instrument, the capillary cartridge should be modified to accommodate the greater length as described by Weekley and Foley . The migration distance for the complementary ions is then determined as described by Blackney and Foley . As long as the migration distance for the complementary ions exceeds this value, co‐detection is not possible. Both combinations of anion/cation migration distances should be evaluated, and the one that provides better results (i.e., a shorter analysis time and/or better overall resolution) can be adopted. …”

“…When electrokinetic injection is used, the amount of a given analyte injected into the capillary is the sum of their electrophoretic and electroosmotic mobilities; therefore, analytes with a higher electrophoretic mobility are introduced in larger quantity than analytes with lower electrophoretic mobility. This bias can be corrected for in both CE and DOI‐CE . Alternatively, hydrodynamic injection can be utilized.…”

Simultaneous stacking of cationic and anionic compounds in single run capillary zone electrophoresis by two-end field amplified sample injection

“…This procedure [32] was further used for the simultaneous determination of inorganic positive and negative nitrogen species in snow samples in a single CE run. Applications of two-end injection CE for the separation of organic compounds [33][34] have also been reported.…”