Unusual stacking with electrokinetic injection of cationic analytes from micellar solutions in capillary zone electrophoresis

Micelle to cyclodextrin stacking in open-tubular liquid chromatography using capillaries coated with surfactant admicelles

In-line sample concentration by micelle to cyclodextrin stacking (MCDS) in open-tubular liquid chromatography (OT-LC) with UV detection is described. OT-LC of two sets of analytes (small-molecule drugs and neutral alkenylbenzenes) was by the use of a fused-silica capillary that was coated with admicelles of didodecyldimethyl ammonium bromide (DDAB). These admicelles acted as a stationary chromatographic pseudophase. The mobile phase was 25 mM sodium tetraborate in 10% methanol, pH 9.2. MCDS was by long pressure injection of samples prepared in 10 mM hexadecyltrimethyl ammonium bromide (CTAB) in 25 mM sodium tetraborate, pH 9.2 (buffer), followed by injection of 50 mM α-CD in buffer (CD solution). Stacking was by application of voltage at -20 kV prior to pressure-driven OT-LC. The factors that influenced MCDS such as type and concentration of CD, concentration of CTAB in the sample, injection time ratio of the sample and the CD solution and stacking time were studied. Under optimised conditions, sensitivity enhancement factors (SEFs) were between 19 and 23, linear ranges were between 0.5 and 10 µg/mL with r² > 0.99 and inter-day/intra-day repeatability in retention time and peak area were ≤5.6% for the model small-molecule drugs. Application to real samples was by the determination of potentially toxic alkenylbenzenes (SEFs = 10 to 12) in basil-leaf and whole-clove extracts. The assay results were comparable to those obtained from an in-house high-performance liquid chromatography-UV method.

Capillary electrophoresis for the analysis of antidepressant drugs: A review

Depression is a common mental disorder that may lead to major mental health problems, and antidepressant drugs have been used as a treatment of choice to mitigate symptoms of major depressive disorders by ameliorating the chemical imbalances of neurotransmitters in brain. Since abusing antidepressant drugs such as selective serotonin reuptake inhibitors and tricyclic antidepressant drugs can cause severe adverse effects, continuous toxicological monitoring of the parent compounds as well as their metabolites using numerous analytical methods appears pertinent. Among them, capillary electrophoresis has been popularly utilized since the method has a lot of advantages viz. using small amounts of sample and solvents, ease of operation, and rapid analysis. This review paper brings a survey of more than 30 papers on capillary electrophoresis of antidepressant drugs published approximately from 1999 until 2018. It focuses on the reported capillary electrophoresis techniques and their applications and challenges for determining antidepressant drugs and their metabolites. It is organized according to the commonly used capillary zone electrophoresis method, followed by non-aqueous capillary electrophoresis and micellar electrokinetic chromatography, with details on breakthrough findings. Where available, information is given about the background electrolyte used, detector utilized, and sensitivity obtained.