Recent advances of capillary electrophoresis in pharmaceutical analysis

Development and Validation of Novel HPLC Methods for Quantitative Determination of Vitamin D3 in Tablet Dosage Form

In the present work, an efficient isocratic HPLC method was developed for the precise and accurate estimation of vitamin D3 in tablet form. The chromatographic conditions comprised an L3 silica column (5 µm in particle size, 4.6 mm × 250 mm) with a mobile phase n-hexane/ethyl acetate (85:15 v/v) with a flow rate of 2.0 mL/min and a detection wavelength of 292 nm. The new methodology was validated for accuracy, precision, specificity, robustness, and quantification limits according to an official monograph of USP/BP and ICH guidelines. The peak areas of the six replicates of the homogeneous sample were recorded. The mean value obtained was 67,301, and the relative standard deviation (RSD) was 0.1741. The linearity and range were in the acceptable bounds, i.e., 0.999, which was calculated using regression line analysis. The results show that the method is truly acceptable as the RSD, as the flow rate was 0.81%, while for the mobile phase composition, it was 0.72%, which lies in the acceptable range. The limit of detection (LOD) and the limit of quantification (LOQ) values were 0.0539 µg/mL and 0.1633 µg/mL, respectively. The % RSD of the intra and inter-day precision of the method was deemed acceptable according to the international commission for harmonization guidelines. The developed method has potential to be used for the detection and quantification of vitamin D3 during routine analysis for tablets in dosage form.

A Research Journey: Over a Decade of Denaturing and Native-MS Analyses of Hydrophobic and Membrane Proteins in Amgen Therapeutic Discovery

Membrane proteins and associated complexes currently comprise the majority of therapeutic targets and remain among the most challenging classes of proteins for analytical characterization. Through long-term strategic collaborations forged between industrial and academic research groups, there has been tremendous progress in advancing membrane protein mass spectrometry (MS) analytical methods and their concomitant application to Amgen therapeutic project progression. Herein, I will describe a detailed and personal account of how electrospray ionization (ESI) native mass spectrometry (nMS), ion mobility-MS (IM-MS), reversed phase liquid chromatographic mass spectrometry (RPLC-MS), high-throughput solid phase extraction mass spectrometry, and matrix-assisted laser desorption ionization mass spectrometry methods were developed, optimized, and validated within Amgen Research, and importantly, how these analytical methods were applied for membrane and hydrophobic protein analyses and ultimately therapeutic project support and progression. Additionally, I will discuss all the highly important and productive collaborative efforts, both internal Amgen and external academic, which were key in generating the samples, methods, and associated data described herein. I will also describe some early and previously unpublished nano-ESI (nESI) native-MS data from Amgen Research and the highly productive University of California Los Angeles (UCLA) collaboration. I will also present previously unpublished examples of real-life Amgen biotherapeutic membrane protein projects that were supported by all the MS (and IM) analytical techniques described herein. I will start by describing the initial nESI nMS experiments performed at Amgen in 2011 on empty nanodisc molecules, using a quadrupole time-of-flight MS, and how these experiments progressed on to the 15 Tesla Fourier transform ion cyclotron resonance MS at UCLA. Then described are monomeric and multimeric membrane protein data acquired in both nESI nMS and tandem-MS modes, using multiple methods of ion activation, resulting in dramatic spectral simplification. Also described is how we investigated the far less established and less published subject, that is denaturing RPLC-MS analysis of membrane proteins, and how we developed a highly robust and reproducible RPLC-MS method capable of effective separation of membrane proteins differing in only the presence or absence of an N-terminal post translational modification. Also described is the evolution of the aforementioned RPLC-MS method into a high-throughput solid phase extraction MS method. Finally, I will give my opinion on key developments and how the area of nMS of membrane proteins needs to evolve to a state where it can be applied within the biopharmaceutical research environment for routine therapeutic project support.

Development of in silico models to predict viscosity and mouse clearance using a comprehensive analytical data set collected on 83 scaffold-consistent monoclonal antibodies

Biologic drug discovery pipelines are designed to deliver protein therapeutics that have exquisite functional potency and selectivity while also manifesting biophysical characteristics suitable for manufacturing, storage, and convenient administration to patients. The ability to use computational methods to predict biophysical properties from protein sequence, potentially in combination with high throughput assays, could decrease timelines and increase the success rates for therapeutic developability engineering by eliminating lengthy and expensive cycles of recombinant protein production and testing. To support development of high-quality predictive models for antibody developability, we designed a sequence-diverse panel of 83 effector functionless IgG1 antibodies displaying a range of biophysical properties, produced and formulated each protein under standard platform conditions, and collected a comprehensive package of analytical data, including in vitro assays and in vivo mouse pharmacokinetics. We used this robust training data set to build machine learning classifier models that can predict complex protein behavior from these data and features derived from predicted and/or experimental structures. Our models predict with 87% accuracy whether viscosity at 150 mg/mL is above or below a threshold of 15 centipoise (cP) and with 75% accuracy whether the area under the plasma drug concentration-time curve (AUC0-672 h) in normal mouse is above or below a threshold of 3.9 × 106 h x ng/mL.

Nanoemulsion supported microemulsion electrokinetic chromatography coupled with selected preconcentration techniques as an approach for analysis of highly hydrophobic compounds

In this paper, an oil-in-water (O/W) nanoemulsion (NE) prepared by water cold dilution of an O/W microemulsion (ME) was introduced as a sample matrix in microemulsion electrokinetic capillary chromatography (MEEKC) for the highly hydrophobic compounds analysis. Several model compounds with log P_O/W values in the 4.1-10.9 range, from different chemical groups, including retinol, α-tocopherol, cholecalciferol, phylloquinone, menaquinone-7, dichlorodiphenyltrichloroethane, ivermectin have been tested. As a proof of the concept of NE formation, a dynamic light scattering technique was employed to determine the size distribution profile of NE particles. Moreover, due to relatively low conductivity of the NE matrix (50-100 times lower in comparison to the separation buffer) and a negative electric charge provided to hydrophobic compounds through NE dispersed phase, NE matrices have been combined with preconcentration techniques based on electrokinetic dosing, namely field amplified sample injection (FASI) and pressure assisted electrokinetic injection (PAEKI). The detection limits for vitamin K₁ and K₂-MK7 in the NE matrix in combination with FASI (NE-MEEKC-FASI) as well as PAEKI (NE-MEEKC-PAEKI) were up to 42.9 and 12.1 ng mL^-1, respectively. In comparison to standard hydrodynamic injection for microemulsion sample matrix NE-MEEKC-PAEKI grant 45-fold improvement in signal sensitivity. The study presents an innovative approach, as it enables the use of preconcentration techniques for highly hydrophobic compounds (log P_O/W > 4), which was not previously possible for implementation in the electromigration techniques. Likewise, the use of organic solvents has been reduced by using ME as a solvent for stock solutions and diluting with water prior to the analysis. The application to real samples was investigated using a dietary supplement containing vitamin K₂-MK7 obtained from the fermentation product of soybeans.

Determination of the pharmaceuticals-nano/microplastics in aquatic systems by analytical and instrumental methods

Pharmaceutical residues and nanoplastic and microplastic particles as emerging pollutants in the aquatic environment are a subject of increasing concern in terms of the effect on water sources and marine organisms. There is lack of information about pharmaceutical-nanoplastic and pharmaceutical-microplastic mixtures. The present study aimed to investigate the fate and effect of pharmaceutical residues and nanoplastic and microplastic particles, the results of combinations of pharmaceutical residues with nanoplastic and microplastic particles, and toxic effects of pharmaceutical residues and nanoplastic and microplastic particles. Moreover, the objective was also to introduce analytical methods for pharmaceuticals, along with instrumental techniques for nanoplastic and microplastic particles in aquatic environments and organisms. PhAC alone can affect marine environments and aquatic organisms. When pharmaceutical residues combine with nanoplastic and microplastic particles, the rate of toxicity increases, and the result of this phenomenon constitutes this kind of pollutant in wastewater. Hence, the rate of mortality in organisms enhances. This study aimed to investigate the effect of pharmaceuticals residues and nanoplastic and microplastic particles, and a mixture of pharmaceutical residues and nanoplastic and microplastic particles in aquatic biota. Another object was survey methods for recognizing pharmaceutical residues and nanoplastic and microplastic particles. The findings show that pharmaceutical residues in organisms caused cell structure damage, inflammatory response, and nerve cell apoptosis. This study aimed to investigate the effect of microplastic particles in the human food chain and their impact on human health. Moreover, this review aims to present an innovative methodology based on comprehensive analytical techniques used to determine and identify pharmaceuticals adsorbed on nano- and microplastics in aquatic ecosystems. Finally, this review addresses the knowledge gaps and provides insights into future research strategies to better understand their interactions.

Sensitivity enhancement in capillary electrophoresis and their applications for analyses of pharmaceutical and related biochemical substances

This review aims to illustrate sensitivity enhancement methods in capillary electrophoresis (CE) and their applications for pharmaceutical and related biochemical substance analyses. The first two parts of the article describe the introduction and principle of CE. The main part focuses on strategies for sensitivity improvement in CE including detector and capillary technologies and pre-concentration techniques. Applications of these techniques for pharmaceutical and biomedical substance analyses are surveyed during the years 2018-2021. This article is protected by copyright. All rights reserved.

SU8/glass microchip capillary electrophoresis integrated with Pt electrodes for separation and simultaneous detection of phenylephrine and acetaminophen

Introduction: A new microfluidic-based method with electrochemical detection was developed for the simultaneous quantification of acetaminophen (AP) and phenylephrine (PHE) pharmaceuticals in the human blood and pharmaceuticals (e.g. tablet and drop).

Methods: The separation was achieved on a SU8/glass microchip with a 100 µm Pt working electrode that was positioned out of the channel and 2-(N-morpholino) ethanesulfonic acid was used as a running buffer (pH 7, 10 mM). Home designed modulated high voltage power supply and dual time switcher was used for controlling the injection and separation of the analytes in the unpinched injection mode.

Results: The injection was carried out using +750 V for 7 seconds, and the separation and detection voltages were set at +1000 V and +0.9 V, respectively. Critical parameters such as detection potential, buffer concentration, injection, and separation voltage were studied in terms of their effects on the resolution, peak height, and migration times. For each analyte, the correlation coefficients were over 0.99 (n = 6). The developed microchip was able to detect AP and phenylephrine simultaneously with the limit of detection of 7.9 and 5.2 (µg/mL) respectively for PHE and AP and excellent linear range of 10-200 (µg/mL). The recovery of the drugs ranged from 96% to 103%, while the repeatability of the method through inter- and intra-day was lower than 7%.

Conclusion: The developed method offers several advantages, including easy sample pretreatment process, simplicity, very fast analysis compared to other typical chromatographic methods. Thus, the proposed microfluidic-based method is proposed to be used as a time- and cost-effective monitoring method for the analysis of AP and PHE.

CE-DAD-MS/MS in the simultaneous determination and identification of selected antibiotic drugs and their metabolites in human urine samples

In this study, a new analytical method was developed and validated for the simultaneous analysis of antibiotic drugs (amoxicillin, cefotaxime, ciprofloxacin, clindamycin, linezolid, metronidazole) and their metabolites (amoxycilloic acid, amoxicillin diketopiperazine, 3-desacetyl cefotaxime lactone, clindamycin sulfoxide, ciprofloxacin piperazinyl-N4-sulfate, linezolid N-oxide, metronidazole-OH) in human urine. Capillary electrophoresis (CE) along with the tandem mass spectrometry (MS/MS) was used to determine and identify all analytes. Appropriate conditions for MS/MS measurements along with the use of the central composite design were optimized. The effects of different analytical conditions (the composition, the concentration, and the pH value of the background electrolyte, the time and pressure of the injection, the capillary temperature and influence of the organic modifier) on the migration and separation of antibiotic drugs and metabolites were examined using the CE-DAD. The analytical procedure was linear for concentrations ranging from 20 to 1000 ng/mL, with determination coefficients higher than 0.99 for all the analytes. The validated analytical procedure was then applied to the measurement of antibiotic drugs and their metabolites in human urine samples.

The impact of chirality on the analysis of alkaloids in plant

Most of the alkaloids are chiral compounds and are clinically administered as the racemic mixture, even though its enantiomers have been known to exert different pharmacological activity. The determination of the enantiomeric composition of alkaloid-containing plants is subject to severe attention from pharmacological and toxicological points of view. This review gives an overview of the chiral analysis of alkaloids that were used in theoretical studies and applications for plants in recent years.

Denaturing and Native Mass Spectrometric Analytics for Biotherapeutic Drug Discovery Research: Historical, Current, and Future Personal Perspectives

Mass spectrometry (MS) plays a key role throughout all stages of drug development and is now as ubiquitous as other analytical techniques such as surface plasmon resonance, nuclear magnetic resonance, and supercritical fluid chromatography, among others. Herein, we aim to discuss the history of MS, both electrospray and matrix-assisted laser desorption ionization, specifically for the analysis of antibodies, evolving through to denaturing and native-MS analysis of newer biologic moieties such as antibody-drug conjugates, multispecific antibodies, and interfering nucleic acid-based therapies. We discuss challenging therapeutic target characterization such as membrane protein receptors. Importantly, we compare and contrast the MS and hyphenated analytical chromatographic methods used to characterize these therapeutic modalities and targets within biopharmaceutical research and highlight the importance of appropriate MS deconvolution software and its essential contribution to project progression. Finally, we describe emerging applications and MS technologies that are still predominantly within either a development or academic stage of use but are poised to have significant impact on future drug development within the biopharmaceutic industry once matured. The views reflected herein are personal and are not meant to be an exhaustive list of all relevant MS performed within biopharmaceutical research but are what we feel have been historically, are currently, and will be in the future the most impactful for the drug development process.

Experimental and computational study on the enantioseparation of four chiral fluoroquinolones by capillary electrophoresis with sulfated-β-cyclodextrin as chiral selector

In this work, enantioseparation of four chiral fluoroquinolones (FQs), namely, ofloxacin, gemifloxacin, lomefloxacin, and gatifloxacin, was achieved by capillary electrophoresis with sulfated-β-cyclodextrin (S-β-CD) as chiral selector. Factors affecting the enantiomeric resolution, such as the concentrations of S-β-CD, BGE pH conditions, and the buffer types and concentrations, were optimized and discussed. A BGE consisting of 30 g/L S-β-CD and 30-mM phosphate at pH 4.0 was found fit for enantiomeric resolution of ofloxacin and gemifloxacin, while the same BGE at pH 3.0 was suitable for enantioseparation of lomefloxacin and gatifloxacin. The pH-dependent experiments showed that separation resolutions of four FQs enantiomers were significantly affected by BGE pH, which was thought to be related with the varying electrostatic attraction between the enantiomers and chiral selector. To verify this speculation, molecular docking studies were used for further investigation of the enantiomeric recognition mechanism of S-β-CD. Molecular model indicated that hydrophobic effect and hydrogen bond were involved in host-guest inclusion, but the electrostatic attraction enhanced the chiral discrimination by increasing the difference in binding energy between individual enantiomers and S-β-CD. This work provided a further insight into the chiral recognition mechanisms of CD derivatives.

Capillary electrophoresis methods for impurity profiling of drugs: A review of the past decade

Capillary electrophoresis (CE) is widely used for the impurity profiling of drugs that contain stereochemical centers in their structures, analysis of biomolecules, and characterization of biopharmaceuticals. Currently, CE is the method of choice for the analysis of foodstuffs and the determination of adulterants. This article discusses the general theory and instrumentation of CE as well as the classification of various CE techniques. It also presents an overview of research on the applications of different CE techniques in the impurity profiling of drugs in the past decade. The review briefly presents a comparison between CE and liquid chromatography methods and highlights the strengths of CE using drug compounds as examples. This review will help scientists, fellow researchers, and students to understand the applications of CE techniques in the impurity profiling of drugs.

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An overview of research related to the use of capillary electrophoresis in the impurity profiling of drugs is presented.

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The principle, instrumentation, and different types of capillary electrophoresis (CE) methods are outlined here.

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Applications of different of CE methods with the chemical structures of drugs and their impurities are highlighted.

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A brief description is also provided on the analysis of Pharmacopeial monographs using CE methods.

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A comparison of CE with liquid chromatography for impurity profiling and analysis of drugs is presented in this review.

Mechanistic studies of droplet electrophoresis: A review

Electrophoresis (EP) of droplets is an intriguing phenomenon that has applications in biological systems, separation strategies, and reactor engineering. Droplet EP is significantly different from the classic particle EP because of droplet characteristics such as a mobile surface charge and the nonrigidity of the interface. Also, the liquid-liquid system, where there is an interplay between the hydrodynamic and electrokinetic forces in both phases, adds to the complexity of electrophoretic motion. Due to the vast amount of potential applications of droplet EP, a mechanistic understanding of the droplet motion in the presence of an external electric field is crucial. This review provides a background on the mechanism of droplet EP and summarizes the intrinsic interplay between the different relevant forces in these systems. The review also describes the key differences between droplet EP and particle EP, and the impact of these differences on droplet mobility. Additionally, we schematically summarize the effects of key parameters on droplet EP mobility, such as electric double layer polarization, the development of internal flow inside a droplet and boundary effects.

Electrochemical Behavior and Square-Wave Stripping Voltammetric Determination of Roflumilast in Pharmaceutical Dosage Forms

BACKGROUND

Bronchial asthma and chronic obstructive pulmonary disease (COPD) are among the most common chronic diseases. Roflumilast is a novel, potent, selective, and long-acting phosphodiesterase 4 (PDE-4) inhibitor for the treatment of bronchial asthma and COPD. It has anti-inflammatory effects, and it has been shown to reduce exacerbations and improve pulmonary function in patients with COPD. Although there have been some other analytical methodologies reported for the determination of roflumilast in pharmaceutical dosage forms, there has not yet been any electrochemical methodology proposed for determination of this unique active pharmaceutical ingredient in its dosage forms.

OBJECTIVE

The aim of this study was to develop an easily applied, selective, sensitive, accurate, and precise square-wave stripping voltammetric (SWSV) method for the determination of roflumilast in its pharmaceutical dosage forms. In addition, the electrochemical behavior of roflumilast was investigated.

METHODS

The proposed method was based on electrochemical reduction of roflumilast at a hanging mercury drop electrode (HMDE) in 0.1 M K2HPO4 and 0.1 M Na2B4O7 (1:1, v/v) buffer at pH 5.0. Two reduction peaks were observed at -1150 mV and -1260 mV with 30 s of accumulation time and -850 mV of accumulation potential time versus Ag/AgCl reference electrode.

RESULTS

The highest peak current values with the best peak definition were observed at a frequency of 50 Hz, scan increment of 5 mV, and pulse amplitude 25 mV. The proposed method was validated by evaluating validation parameters such as linearity, sensitivity, repeatability, accuracy, precision, selectivity, recovery, robustness, and ruggedness. A good linear correlation (r=0.9948) was obtained between the electrochemical response of roflumilast and its concentration in the range of 0.74-3.05 μg mL-1 under the optimum conditions. The obtained accuracy results were between 2.04% and -2.04% while the relative standard deviation of the results was at least 2.78% for intraday and inter-day studies. The mean recovery for the real applications was 100.63% ± 0.52. The electrochemical behavior of roflumilast was investigated by cyclic voltammetry. The cyclic voltammogram of roflumilast exhibited two peaks and the reduction reaction was reversible.

CONCLUSION

This developed and validated SWSV method was applied successfully for the determination of roflumilast in tablet dosage form (Daxas®) to assess active roflumilast content. Since high- -performance liquid chromatography is a dominant technique in industry for quality control of active pharmaceutical ingredients, the finding in the present study demonstrated that square-wave stripping voltammetry could be easily utilized in routine applications to determine roflumilast content in its dosage forms.

Development of a CE-MS method for the study of riociguat and metabolite M1 in pharmaceutical analysis

Riociguat is a novel antihypertensive drug for the treatment of pulmonary hypertension. We present electrophoretic characterization, i.e. migration behavior of riociguat and metabolite M1 as support for optimized CZE/MS assay. Fundamental separation parameters, such as peak width, symmetry, and resolution are studied in a series of ammonium formate buffers within pH range 2.60-5.61. The narrow region of peak symmetry lies close to pH 4.0 for both analytes. Accordingly, the value of resolution maximizes in a background electrolyte adjusted to pH 4.10. Basic calibration parameters estimated from CZE experiments with absorption photometric and mass spectrometric detection of riociguat and metabolite M1 were evaluated. More than three orders lower LOD was achieved with high resolution mass spectrometric detection. The observed difference in the sensitivity of both detection techniques gives priority to the utilization of CZE/MS in practice. The values of dissociation constants of riociguat and metabolite M1, pK_BH , were determined from CZE measurements in lithium formate and lithium acetate background electrolytes with constant ionic strength. The value of pK_BH = 4.30 ± 0.02 for riociguat corresponds well to the value already presented in the literature. According to our observation, metabolite M1 behaves like a slightly stronger base with estimated pK_BH = 4.40 ± 0.02.

Distribution and Chemical Analysis of Pharmaceuticals and Personal Care Products (PPCPs) in the Environmental Systems: A Review

PPCPs are found almost everywhere in the environment especially at an alarming rate and at very low concentration in the aquatic systems. Many methods-including pressurized hot water extraction (PHWE), pressurized liquid extraction (PLE), ultrasound-assisted extraction (UAE), and micro-assisted extraction (MAE)-have been employed for their extraction from both surface waters and biota. Solid-phase extraction (SPE) proved to be the best extraction method for these polar, non-volatile, and thermally unstable compounds in water. However, ultrasonic extraction works better for their isolation from sediment because it is cheap and consumes less solvent, even though SPE is preferred as a clean-up method for sediment samples. PPCPs are in groups of-acidic (e.g., diclofenac, ibuprofen, naproxen), neutral (e.g., caffeine, carbamazepine, fluoxetine), and basic pharmaceuticals, as well as antibiotics and estrogens amongst others. PPCPs which are present in trace levels (ng/L) are more often determined by liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), and high-performance liquid chromatography-ultraviolent (HPLC-UV). Of these, LC-MS and LC-MS-MS are mostly employed for the analysis of this class of compounds, though not without a draw-back of matrix effect. GC-MS and GC-MS-MS are considered as alternative cost-effective methods that can also give better results after derivatization.

Characterization of New Cyclic D,L-α-Alternate Amino Acid Peptides by Capillary Electrophoresis Coupled to Electrospray Ionization Mass Spectrometry

The self-assembly of peptide nanotubes (PNTs) depends on the structure and chemistry of cyclic peptide (CP) monomers, impacting on their properties, which makes the choice of their monomers and their characterization a high challenge. For this purpose, we developed for the first time a capillary electrophoresis coupled to electrospray ionization mass spectrometry (CE-ESI-MS) methodology and characterized a set of eight original CP sequences of 8, 10, and 12 D,L-α-alternate amino acids with a controlled internal diameter (from 7 to 13 Å) and various properties (diameter, global surface charge, hydrophobicity). This new CE-ESI-MS methodology allows verifying the structure, the purity, as well as the stability (when stored during several months) of interesting potential precursors for PNTs that could be employed as nanoplatforms in diagnostics or pseudo sieving tools for separation purposes.

Recent advances in open tubular capillary liquid chromatography

This review covers advances and applications of open tubular capillary liquid chromatography (OT-LC) over the period 2007–2018.

The Use of a 3D-Printed Microfluidic Device and Pressure Mobilization for Integrating Capillary Electrophoresis with Electrochemical Detection

Capillary electrophoresis coupled with electrochemical detection can be a powerful analysis tool; however, previous methods developed to integrate these two techniques can often times be fragile and have alignment issues such that there are no commercially available approaches. In this paper, we present the use of a 3D-printed Wall-Jet Electrode device for integrating capillary electrophoresis with electrochemical detection. A pressure mobilization step was also utilized to further reduce noise by allowing the electrophoresis separation step to continue only until the first analyte was close to elution. Then, the separation voltage was terminated and pressure-based flow was used for elution of the analyte bands onto the electrode surface with a wall-jet configuration. It is shown that the pressure-based elution is beneficial for the reduction of baseline noise and elimination of field effects. A mixture of catecholamines were separated to demonstrate effectiveness of the system. In addition, the system was coupled with a Beckman Coulter commercial capillary electrophoresis instrument in a straightforward manner. The system was also shown to be effective in separations done with a high ionic strength physiological buffer. This 3D printing approach can be used by researchers to utilize electrochemical detection on commercial capillary electrophoresis systems by downloading the provided STL and/or CAD files.

Development of a capillary electrophoresis method for the determination of the chiral purity of dextromethorphan by a dual selector system using quality by design methodology

Dextromethorphan is a centrally acting antitussive drug, while its enantiomer levomethorphan is an illicit drug with opioid analgesic effects. As capillary electrophoresis has been proven as an ideal technique for enantiomer analysis, the present study was conducted in order to develop a capillary electrophoresis-based limit test for levomethorphan. The analytical target profile was defined as a method that should be able to determine levomethorphan with acceptable precision and accuracy at the 0.1 % level. From initial scouting experiments, a dual selector system consisting of sulfated β-cyclodextrin and methyl-α-cyclodextrin was identified. The critical process parameters were evaluated in a fractional factorial resolution IV design followed by a central composite face-centered design and Monte Carlo simulations for defining the design space of the method. The selected working conditions consisted of a 30/40.2 cm, 50 μm id fused-silica capillary, 30 mM sodium phosphate buffer, pH 6.5, 16 mg/mL sulfated β-cyclodextrin, and 14 mg/mL methyl-α-cyclodextrin at 20°C and 20 kV. The method was validated according to ICH guideline Q2(R1) and applied to the analysis of a capsule formulation. Furthermore, the apparent binding constants between the enantiomers and the cyclodextrins as well as complex mobilities were determined to understand the migration behavior of the analytes.

Capillary Electrophoresis Hyphenated with Mass Spectrometry for Determination of Inflammatory Bowel Disease Drugs in Clinical Urine Samples

Azathioprine is the main thiopurine drug used in the treatment of immune-based inflammations of gastrointestinal tract. For the purpose of therapy control and optimization, effective and reliable analytical methods for a rapid drug monitoring in biological fluids are essential. Here, we developed a separation method based on the capillary electrophoresis (CE) hyphenated with tandem mass spectrometry (MS/MS) for the simultaneous determination of azathioprine and its selected metabolites (6-thioguanine, 6-mercaptopurine, and 6-methylmercaptopurine) as well as other co-medicated drugs (mesalazine, prednisone, and allopurinol). The optimized CE-MS/MS conditions provided a very efficient and stable system for the separation and sensitive detection of these drugs in human urine matrices. The developed method was successfully applied for the assay of the targeted drugs and their selected metabolites in urine samples collected from patients suffering from inflammatory bowel disease (IBD) and receiving azathioprine therapy. The developed CE-MS/MS method, due to its reliability, short analysis time, production of complex clinical profiles, and favorable performance parameters, evaluated according to FDA guidelines for bioanalytical method validation, is proposed for routine clinical laboratories to optimize thiopurine therapy, estimate enzymatic activity, and control patient compliance with medication and co-medication.

Derivatisation for separation and detection in capillary electrophoresis (2015-2017)

Derivatisation is an integrated part of many analytical workflows to enable separation and detection of the analytes. In CE, derivatisation is adapted in the four modes of pre-capillary, in-line, in-capillary, and post-capillary derivatisation. In this review, we discuss the progress in derivatisation from February 2015 to May 2017 from multiple points of view including sections about the derivatisation modes, derivatisation to improve the analyte separation and analyte detection. The advancements in derivatisation procedures, novel reagents, and applications are covered. A table summarising the 46 reviewed articles with information about analyte, sample, derivatisation route, CE method and method sensitivity is provided.

Letrozole Determination by Capillary Zone Electrophoresis and UV Spectrophotometry Methods

Objective: Letrozole is a highly potent oral nonsteroidal aromatase inhibitor triazole derivative. The aim of this study was to quantify letrozole from bulk, pharmaceutical formulation, and spiked urine samples by developing a simple, rapid and cost effective capillary electrophoresis method. Methods: A capillary zone electrophoresis method was optimized and validated. Additionally, an UV spectrophotometry method was used for comparing results. Results:The capillary zone electrophoresis method using a 90 mM sodium tetraborate background electrolyte proved to be an efficient method for determination of letrozole in a very short time, less than 2 minutes, using 20 kV voltage, 50 mbar/2 seconds pressure and 50°C temperature as optimum parameters. Additionally, the UV spectrophotometry method proved to be simple and efficient to quantify letrozole from bulk material and pharmaceutical formulation with linearity of response between 5 to 20 μg·mL-1 concentrations. For both methods, validation parameters, including linearity, detection and quantification limits were determined. Also we proved that our electrophoretic method has potential in analyzing letrozole from biological samples, obtaining encouraging results on estimation of letrozole from spiked urine samples without any special treatment. Conclusions: To quantify letrozole from bulk material, pharmaceutical preparations, and spiked urine samples the capillary zone electrophoresis method using a tetraborate sodium background electrolyte has proven to be simple and appropriate. Also a simple UV spectrophotometric method has been developed and validated for the same purposes.

Novel volumetric method for highly repeatable injection in microchip electrophoresis

A novel injector for microchip electrophoresis (MCE) has been designed and evaluated that achieves very high repeatability of injection volume suitable for quantitative analysis. It eliminates the injection biases in electrokinetic injection and the dependence on pressure and sample properties in hydrodynamic injection. The microfluidic injector, made of poly(dimethylsiloxane) (PDMS), operates similarly to an HPLC injection valve. It contains a channel segment (chamber) with a well-defined volume that serves as an "injection loop". Using on-chip microvalves, the chamber can be connected to the sample source during the "loading" step, and to the CE separation channel during the "injection" step. Once the valves are opened in the second state, electrophoretic potential is applied to separate the sample. For evaluation and demonstration purposes, the microinjector was connected to a 75 μm ID capillary and UV absorbance detector. For single compounds, a relative standard deviation (RSD) of peak area as low as 1.04% (n = 11) was obtained, and for compound mixtures, RSD as low as 0.40% (n = 4) was observed. Using the same microchip, the performance of this new injection technique was compared to hydrodynamic injection and found to have improved repeatability and less dependence on sample viscosity. Furthermore, a non-radioactive version of the positron-emission tomography (PET) imaging probe, FLT, was successfully separated from its known 3 structurally-similar byproducts with baseline resolution, demonstrating the potential for rapid, quantitative analysis of impurities to ensure the safety of batches of short-lived radiotracers. Both the separation efficiency and injection repeatability were found to be substantially higher when using the novel volumetric injection approach compared to electrokinetic injection (performed in the same chip). This novel microinjector provides a straightforward way to improve the performance of hydrodynamic injection and enables extremely repeatable sample volume injection in MCE. It could be used in any MCE application where volume repeatability is needed, including the quantitation of impurities in pharmaceutical or radiopharmaceutical samples.

Design, synthesis, and characterization of new cyclic d,l-α-alternate amino acid peptides by capillary electrophoresis coupled to electrospray ionization mass spectrometry

The self-assembly of peptide nanotubes (PNTs) depends on the structure and chemistry of cyclic peptide (CP) monomers, having an impact on their properties, making the choice of their monomers and their characterization a great challenge. We synthesized for the first time a new set of eight original CP sequences of 8, 10, and 12 d,l-α-alternate amino acids with a controlled internal diameter from 7 to 13 Å. They present various properties (e.g., diameter, global surface charge, hydrophobicity) that can open the way to new applications. Their structure and purity were determined thanks to a capillary electrophoresis coupled to electrospray ionization mass spectrometry (CE-ESI-MS) methodology developed for the first time for this purpose. The CPs were successfully separated in a basic hydro-organic background electrolyte (BGE, pH 8.0, H2O/EtOH 50:50, v/v) and analyzed in MS positive mode. The effect of CP structure on electrophoretic mobility was studied, and the mass spectra were deeply analyzed. This methodology allowed verifying their purity and the absence of linear peptide precursors as well as their stability when stored over several months. Therefore, we have developed a new CE-ESI-MS methodology for the structure and purity control of interesting potential precursors for PNTs that could be employed as nanoplatforms in diagnostics or as pseudo sieving tools for separative purposes.

Significance and challenges of stereoselectivity assessing methods in drug metabolism

Stereoselectivity in drug metabolism can not only influence the pharmacological activities, tolerability, safety, and bioavailability of drugs directly, but also cause different kinds of drug-drug interactions. Thus, assessing stereoselectivity in drug metabolism is of great significance for pharmaceutical research and development (R&D) and rational use in clinic. Although there are various methods available for assessing stereoselectivity in drug metabolism, many of them have shortcomings. The indirect method of chromatographic methods can only be applicable to specific samples with functional groups to be derivatized or form complex with a chiral selector, while the direct method achieved by chiral stationary phases (CSPs) is expensive. As a detector of chromatographic methods, mass spectrometry (MS) is highly sensitive and specific, whereas the matrix interference is still a challenge to overcome. In addition, the use of nuclear magnetic resonance (NMR) and immunoassay in chiral analysis are worth noting. This review presents several typical examples of drug stereoselective metabolism and provides a literature-based evaluation on current chiral analytical techniques to show the significance and challenges of stereoselectivity assessing methods in drug metabolism.

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis

Since the introduction about 30 years ago, CE techniques have gained a significant impact in pharmaceutical analysis. The present review covers recent advances and applications of CE for the analysis of pharmaceuticals. Both small molecules and biomolecules such as proteins are considered. The applications range from the determination of drug-related substances to the analysis of counterions and the determination of physicochemical parameters. Furthermore, general considerations of CE methods in pharmaceutical analysis are described.

Study on an electrochromatography method based on organic-inorganic hybrid molecularly imprinted monolith for determination of trace trichlorfon in vegetables

BACKGROUND

Organophosphorus pesticides have been widely used in agricultural production. However, the wide use of organophosphate also results in pesticide residues on the plant, which are harmful to human health because of their potential mutagenic and carcinogenic properties. Therefore, it is vital to develop a sensitive and effective analysis method to control pesticide residues.

RESULTS

In this study, a novel molecularly imprinted capillary monolithic column was prepared using trichlorfon as the template molecule by combining non-hydrolytic sol-gel process with a molecular imprinting technique. The resulting material was characterized by scanning electron microscopy and Fourier transform infrared. Under capillary electrochromatography, the effects of voltage, pH, ACN content and concentration of buffer solution on the electro-osmotic flow (EOF) of imprinted capillary monolithic column were evaluated in detail. Using this prepared material as stationary phase for capillary electrochromatography, a novel method of molecularly imprinted capillary electrochromatography (MICEC) for the detection of trace trichlorfon residues in vegetables was developed. Under optimal conditions, appreciable sensitivity was achieved with a LOD (S/N = 3) of 92.5 µg kg(-1) and method quantitation limit (MQL) of 305.3 µg kg(-1), respectively. The linear ranges of the calibration graph were 0.1 µg L(-1) to 10 mg L(-1). The peak area precision (RSD) for five replicate extractions of 0.01 mg L(-1) trichlorfon standard aqueous solution was 4.5%. To evaluate the accuracy of this method, the blank cucumber and cauliflower samples spiked with trichlorfon were extracted and analyzed by this method with good recoveries, ranging from 80.2% to 95.8%. Moreover, this method was successfully applied to the quantitative detection of the trichlorfon residues in leek samples.

CONCLUSION

With good properties of high sensitivity and simple pre-treatment, this MICEC method could provide a new tool for the rapid determination of trace trichlorfon residue in complex food samples.