Combination of poly(diallyldimethylammonium chloride) and hydroxypropyl-γ-cyclodextrin for high-speed enantioseparation of phenothiazines by capillary electrophoresis

Ultrasensitive determination of 10 phenothiazine derivatives and their enantiomers in biological fluids by capillary electrophoresis with contactless conductivity detection

In this study, a simple, rapid, and ultrasensitive technique was developed to identify five pairs of phenothiazine drugs by using ultrasound-enhanced and surfactant-assisted dispersive liquid-liquid microextraction (UESA-DLLME), field-amplified sample injection with capillary electrophoresis (FASI-CE), and capacitively coupled capacitively coupled contactless conductivity detection (C4D). During the CE separation process, UESA-DLLME was used for sample clean-up and offline concentration, and FASI-CE was used for the online concentration of phenothiazine enantiomers. At baseline, the five pairs of phenothiazine enantiomer drugs required 18 min for separation. UESA-DLLME was then used to extract 0.01 mM Tween 80 at pH 10 from a sample solution (extraction solvent, 100 mL of dichloromethane). Subsequently, FASI was used to stack the sample solution (buffer, 30 mM 2-(N-morpholino)ethanesulfonic acid/aspartic acid, additive 4 mM hydroxypropyl-γ-cyclodextrin, pH 2.5), and C4D was used for signal detection (amplitude, 2 Vpp; frequency, 400 kHz). The results indicated that the linear range for quantifying all analyte enantiomers was 1.0-150 nM, with a coefficient of determination exceeding 0.99. In addition, the relative standard deviations in the migration time and peak areas for the 10 analytes were less than 3.2% and 7.2%, respectively. The proposed system has a limit of detection (LOD) for the 10 analytes at a signal-to-noise ratio of 3, ranging from 0.24 to 0.28 nM. The sensitivity enhancement, which compares the LOD0 (limit of detection in the normal method) to LOD1 (limit of detection achieved using the proposed UESA-DLLME-FASI-CE-C4D method), varies between approximately 1200 and 2000 for the 10 analytes. Analysis of the 10 separated analytes spiked in urine and serum samples revealed recovery rates of 88%-106% and 89%-105%, respectively. Therefore, this highly sensitive advanced technique was successfully used to analyze phenothiazine enantiomers in urine and serum samples.

Ultrasensitive analysis of mirtazapine and its metabolites enantiomers in body fluids using ultrasound-enhanced and surfactant-assisted dispersive liquid-liquid microextraction followed by polymer-mediated stacking in capillary electrophoresis

A simple, rapid, and sensitive technique for measuring mirtazapine and its metabolites enantiomers in human fluids, such as urine and serum, was developed by applying ultrasound-enhanced and surfactant-assisted dispersive liquid-liquid microextraction (USA-DLLME) integrated with poly(diallyldimethylammonium chloride) (PDDAC)-mediated stacking in capillary electrophoresis (CE). The parameters that affect extraction and stacking performance, such as the extraction volume, surfactant types, surfactant concentrations, salt additives, extraction time, solution pH, and background electrolytes, were comprehensively studied and optimized to achieve optimal detection performance. Under optimal extraction conditions (injection of 120 µL of C₂H₂Cl₄ into 1 mL of a sample solution containing 0.05 mM Brij-35 at pH 10.0) and separation conditions (0.9% PDDAC, 10 mM phosphate, pH 3.0, and 20 mM dimethyl-β-cyclodextrin), on-line CE stacking of mirtazapine-related chiral drugs was achieved by the two strategies: (i) neutral DM-β-CD sweep low concentrations of DL-NaSSA and (ii) DL-NASSA is stacked by the difference in the viscosity between the PDDAC and sample zone. An approximately 2,800-4000-fold improvement in detection sensitivity was revealed for mirtazapine, N-demethylmirtazapine, and 8-hydroxymirtazapine enantiomers. The linear ranges for the quantification of all analyte enantiomers were 1.2-150 nM, with a coefficient of determination higher than 0.99; the relative standard deviations in the migration time and peak areas for six analytes were less than 1.8% and 5.8%, respectively. The proposed system provided the limits of detection (signal-to-noise ratio of 3) of the six analytes as 0.3-0.5 nM. The recovery of the six separated analytes spiked in urine and serum samples was revealed to be 82.7%-109.5% and 91%-112.8%, respectively. This advanced technique with high sensitivity enhancement factors was successfully employed to analyze mirtazapine and its metabolites enantiomers in urine and serum samples with reliability.

Enantiomeric Determination of Drugs in Pharmaceutical Formulations and Biological Samples by Electrokinetic Chromatography

Chirality is a relevant issue in the pharmaceutical field due to the different biological activity that enantiomers of a chiral drug can show. In fact, the desired biological or pharmaceutical activity might be present in only one of the enantiomers, while the other enantiomer(s) may have different biological activity, be inactive or even toxic. This has motivated in recent years the development of drugs marketed as pure enantiomers to avoid exposing the organism to the action of enantiomers that may not be active or even harmful to health. Thus, it is of high interest to develop enantioselective analytical methodologies to control the presence of enantiomeric impurities and to understand the enantioselective metabolism of chiral drugs. This review gives an overview about the analytical strategies developed by electrokinetic chromatography (EKC) from 2010 to June 2019 for the enantiomeric determination of drugs in both pharmaceutical formulations and biological samples. The types of chiral selectors used, the migration order of enantiomers, their resolution, the detection technique employed and the sensitivity achieved are revised and compared. Also, applications to assess the enantiomeric purity control of pharmaceutical formulations and to determine chiral drugs in biological samples to study their metabolism are included. Advantages and limitations of the chiral methods developed by EKC are also discussed.

Enantioseparation of phenothiazines through capillary electrophoresis with solid phase extraction and polymer based stacking

This study developed a sensitive method involving capillary electrophoresis (CE) coupled with ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugs at nanomolar concentration levels. The method consists of hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector and poly (diallyldimethylammonium chloride) (PDDAC)-based CE. Five pairs of d,l-phenothiazines were baseline separated using a background electrolyte containing 0.9% PDDAC, 5 mM Hp-γ-CD, and 100 mM tris(hydroxymethyl)aminomethane (Tris)-formate (pH 3.0). The five pairs were successfully stacked on the basis of the difference in viscosity between the PDDAC-containing background electrolyte and the sample solution, with almost no loss of resolution. The combination of a solid-phase extraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazine enantiomers. Under optimal conditions, calibration graphs displayed the linear range between 6 and 1500 nM, with relative standard deviation values lower than 3.5% (n = 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-fold enhancement was achieved. The practicality of using the proposed method to determine five pairs of d,l-phenothiazines in urine is also validated, in which recoveries between recoveries of all phenothiazines from urine ranged from 89% to 101%.