Recent progress in pharmacokinetic applications of capillary electrophoresis

This review is a continuation of the previous reviews (Electrophoresis 1999, 20, 3259-3268; Electrophoresis 2001, 22, 4244-4248) to update the recent publications from 2001 to 2003 on pharmacokinetic studies using capillary electrophoresis (CE). During this period of time, CE remains as a unique analytical method for some studies, which would otherwise be limited by many factors, such as the sample volume, detection sensitivity, or separation power. It is particularly noticeable that the separation of chiral drugs in biological sample and the use of solid-phase extraction (SPE) as a simple and convenient means of sample preparation appear to become popular for CE-based assays. The use of CE for assessing complete pharmacokinetic information, however, did not show a significant growth during this period of time. In order to provide a broad range of view on how biological samples are analyzed by CE, this review will cover publications during the past two years on the use of CE for the analysis of drugs in biological fluids for general pharmacokinetic applications including drug monitoring and bioavailability studies.     

Pharmacokinetic applications of capillary electrophoresis: a review on recent progress

This article covers recent publications from 2003 to 2005 on the subject of pharmacokinetic applications of CE. Many analytical methods were validated and more importantly, they were shown to have sufficient sensitivities to access pharmacokinetic data on different models. Because of unique advantages, such as simplified sample preparation methods, small sample amount required, high separation power, and speedy analysis, CE-based assays were found to gain popularity not only as a second method but also as a major method for many pharmacokinetic studies.     

Determination of zolpidem, a new sleep-inducing agent, and its metabolites in biological fluids: pharmacokinetics, drug metabolism and overdosing investigations in humans.

For the determination of zolpidem, a new sleep inducer, and its metabolites in human plasma and urine, three methods were developed that are suitable for pharmacokinetics, drug metabolism and overdosing investigations. The methods used for pharmacokinetic and drug metabolism studies are based on column-switching high-performance liquid chromatography; they do not require any sample manipulation because the plasma or diluted urine is injected into a pre-column where clean-up and preconcentration take place. The analytes are transferred by valve-switching to the C18 analytical column for chromatography. To investigate overdose cases, urine samples only are used: the method is simple, because the diluted urine can be injected directly into the analytical column (phenyl type). This allows the identification and quantification of the principal urinary metabolite of zolpidem, the unchanged drug being practically undetectable. All the methods use fluorescence detection, which affords high sensitivity and selectivity. It is necessary to use a method capable of the determination of metabolites even if these are apparently pharmacologically inactive, because in different physiopathological populations the qualitative and quantitative metabolic profiles of zolpidem could be different. The method designed for the investigation of (accidental or deliberate) overdose cases is, as required on such occasions, simple and rapid, with good selectivity with respect to commonly prescribed psychotropic drugs.     

Enantiospecific analysis by capillary electrophoresis: applications in drug metabolism and pharmacokinetics

Enantiospecific analysis has an important role in drug metabolism and pharmacokinetic investigations and its now no longer acceptable to determine total drug, or metabolite, concentrations following the administration of a racemate. Inspite of the fact that capillary electrophoresis (CE) has become an essential technique in pharmaceutical and enantiospecific analysis, the chromatographic methodologies remain the most commonly used approach for the determination of the enantiomeric composition of drugs in biological fluids. The application of CE to bioanalysis has been slow, which is in part associated with the complexity of biological matrices together with the relatively poor concentration limits of detection achievable. However, as a result of its versatility, high separation efficiency, minimal sample requirements, speed of analysis and low consumable expense CE is likely to play an increasingly significant role in the area. This review present an overview of enantiospecific CE in bioanalysis in which the approaches to enantiomeric resolution and the problems associated with biological matrices are briefly discussed. The application of enantiospecific CE to samples of biological origin is illustrated using examples where the methodology has either solved an analytical problem, or provided a useful alternative to the currently available chromatographic methods. Such improvements in methodology are associated with either the high separation efficiency and/or microanalytical capabilities of the technique. Enantiospecific CE will not replace the chromatographic methodologies but does provide the bioanalyst with a useful addition to his armamentarium.     

Recent advances in pharmacokinetic applications of capillary electrophoresis

This article reviews recent capillary electrophoresis (CE)-based assays which were published for pharmacokinetic studies. Both the advantages and disadvantages of these CE-based assays are discussed based on their feasibility and the significance towards the better understanding of pharmacokinetics. In addition, as a future outlook, novel assays such as immunoaffinity CE and chip-based CE for analyzing drugs in biological fluids are summarized in view of their potential for pharmacokinetic applications.     

Enantioselectivity in Drug Pharmacokinetics and Toxicity: Pharmacological Relevance and Analytical Methods

Enzymes, receptors, and other binding molecules in biological processes can recognize enantiomers as different molecular entities, due to their different dissociation constants, leading to diverse responses in biological processes. Enantioselectivity can be observed in drugs pharmacodynamics and in pharmacokinetic (absorption, distribution, metabolism, and excretion), especially in metabolic profile and in toxicity mechanisms. The stereoisomers of a drug can undergo to different metabolic pathways due to different enzyme systems, resulting in different types and/or number of metabolites. The configuration of enantiomers can cause unexpected effects, related to changes as unidirectional or bidirectional inversion that can occur during pharmacokinetic processes. The choice of models for pharmacokinetic studies as well as the subsequent data interpretation must also be aware of genetic factors (such as polymorphic metabolic enzymes), sex, patient age, hepatic diseases, and drug interactions. Therefore, the pharmacokinetics and toxicity of a racemate or an enantiomerically pure drug are not equal and need to be studied. Enantioselective analytical methods are crucial to monitor pharmacokinetic events and for acquisition of accurate data to better understand the role of the stereochemistry in pharmacokinetics and toxicity. The complexity of merging the best enantioseparation conditions with the selected sample matrix and the intended goal of the analysis is a challenge task. The data gathered in this review intend to reinforce the importance of the enantioselectivity in pharmacokinetic processes and reunite innovative enantioselective analytical methods applied in pharmacokinetic studies. An assorted variety of methods are herein briefly discussed.     

毛细管电泳序列分析技术用于在线酶分析研究进展

毛细管电泳技术具有操作简单、样品消耗量少、分离效率高和分析速度快等优势,不仅是一种高效的分离分析技术,而且已经发展成为在线酶分析和酶抑制研究的强有力工具。酶反应全程的实时在线监测,可以实现酶反应动力学过程的高时间分辨精确检测,以更准确地获得反应机制和反应速率常数,有助于更好地了解酶反应机制,从而更全面深入地认识酶在生物代谢中的功能。此外,准确、快速的在线酶抑制剂高通量筛选方法的发展,对加快酶抑制类药物的研发以及疾病的临床诊断亦具有重要意义。电泳媒介微分析法（EMMA）和固定化酶微反应器（IMER）是毛细管电泳酶分析技术中常用的在线分析方法。这两种在线酶分析法的进样方式通常为流体动力学进样和电动进样,无法实现酶反应过程中的无干扰序列进样分析。近年来,基于快速序列进样的毛细管电泳序列分析技术已经发展成为在线酶分析的另一种强有力手段,以实现高时间分辨和高通量的酶分析在线检测。该文从快速序列进样的角度,综述了近年来毛细管电泳序列分析技术在线酶分析的研究进展,并着重介绍了各种序列进样方法及其在酶反应和酶抑制反应中的应用,包括光快门进样、流动门进样、毛细管对接的二维扩散进样、流动注射进样、液滴微流控进样等。     

Comparison of HPLC and CE methods for the determination of cetirizine dihydrochloride in human plasma samples

Two methods, capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC), for analysis of cetirizine dihydrochloride in small sample volumes of human plasma were compared. The CE and HPLC assays were developed and validated by analyzing a series of plasma samples containing cetirizine dihydrochloride in different concentrations using these two methods. The extraction procedure is simple and no complicated purification steps or derivatization are required. The analysis time in the HPLC method was shorter than that in the CE method, but solvent consumption was considerably lower in the CE method. The calibration curve was linear to at least 10-1000 ng/mL both for CE and HPLC with r(2) = 0.9993 and r(2) = 0.9994, respectively. The detection limits for cetirizine dihydrochloride were 3 and 5 ng/mL with CE and HPLC (a UV detector was applied in the both cases), respectively. Both methods were selective, robust and specific, allowing reliable quantification of cetirizine dihydrochloride, and could be useful for clinical and biomedical investigations.     

High-performance liquid chromatography coupled to mass spectrometry for studying new pharmaceutical entities

The review covers the aspects of the use of high-performance liquid chromatography coupled to mass spectrometry for studying new pharmaceutical entities. Attention is paid mainly to pharmacokinetic investigations. Different methods of sample preparation and approaches to minimize the duration of the analysis are discussed.     

Special aspects of detection methodology in nonaqueous capillary electrophoresis

Over the recent years considerable efforts have been directed to the design of powerful detector arrangements for capillary electrophoresis (CE). The analytical characteristics of the detector have a great influence on the overall analytical performance of CE investigations. The major detection methods in CE, such as UV-Vis absorbance, fluorescence, mass spectrometry and electrochemical detection, have successfully been adapted also to nonaqueous capillary electrophoresis (NACE). However, the different properties of organic solvent systems require some modification of detector concepts and design compared to aqueous CE. The advances of detector development and application in NACE are reported and discussed with emphasis on methodical aspects.     

CE for cytokinin analyses: a review

Analyses of cytokinins are very important in both plant physiological and biomedical research as they are implicated in many biological processes. Reliable, sensitive, selective and inexpensive methods that are flexible and designed for automation are required for these analyses. This review addresses the advances made in the separation and determination of cytokinins by CE as well as the other applications of CE (i.e., determination of dissociation constants and complexation constants of cytokinins). The various CE modes used to separate the compounds and the quantification strategies are examined. Special attention is also focused on those aspects that improve on the sensitivity and/or selectivity, such as sample extraction and preconcentration, on-line preconcentration techniques (stacking), and/or specific detectors (e.g., MS). With the coupling to the preconcentration techniques and certain detection systems, numerous CE methods can potentially be adapted for the analysis of cytokinins in complex biological samples. Therefore, we would anticipate wider applications of CE methods in the near future for cytokinin analyses, which should facilitate a decrease in analysis cost and should help to improve analysis efficiency.     

On-line microdialysis coupled with microbore liquid chromatography with ultraviolet detection for continuous monitoring of free cefsulodin in rat blood

A microdialysis method followed by a microbore liquid chromatographic ultraviolet detection procedure has been performed for the assay of unbound cefsulodin in rat blood. A microdialysis probe was inserted into the jugular vein for blood sampling. This method involves an on-line design for submitting dialysate into the liquid chromatographic system. The chromatographic conditions consisted of a mobile phase of methanol-100 mM monosodium phosphoric acid (10:90, v/v, pH 5.0) pumped through a microbore reversed-phase column at a flow-rate of 0.05 ml/min. Detection wavelength was set at 265 nm. Microdialysis probes, being laboratory-made, were screened for acceptable in vivo recovery while chromatographic resolution and detection were validated for response linearity as well as intra- and inter-day variabilities. The method was then applied to pharmacokinetics profiling of cefsulodin in the blood following intravenous administration of cefsulodin (20 mg/kg) in rats. Pharmacokinetics were calculated from the corrected data for dialysate concentrations of cefsulodin versus time. Based on pharmacokinetic calculation, cefsulodin best fitted to a two-exponential disposition. This study provided specific pharmacokinetic information for protein-unbound cefsulodin and demonstrated the applicability of this continuous sampling method for pharmacokinetic study.     

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis (2013–2015)

This review updates and follows‐up a previous review by highlighting recent advancements regarding capillary electromigration methodologies and applications in pharmaceutical analysis. General approaches such as quality by design as well as sample injection methods and detection sensitivity are discussed. The separation and analysis of drug‐related substances, chiral CE, and chiral CE‐MS in addition to the determination of physicochemical constants are addressed. The advantages of applying affinity capillary electrophoresis in studying receptor–ligand interactions are highlighted. Finally, current aspects related to the analysis of biopharmaceuticals are reviewed. The present review covers the literature between January 2013 and December 2015.     

Capillary electrophoresis-based immunoassays: principles and quantitative applications

The use of CE as a tool to conduct immunoassays has been an area of increasing interest over the last decade. This approach combines the efficiency, small sample requirements, and relatively high speed of CE with the selectivity of antibodies as binding agents. This review examines the various assay formats and detection modes that have been reported for these assays, along with some representative applications. Most CE immunoassays in the past have employed homogeneous methods in which the sample and reagents are allowed to react in solution. These homogeneous methods have been conducted as both competitive binding immunoassays and as noncompetitive binding immunoassays. Fluorescent labels are most commonly used for detection in these assays, but enzyme labels have also been utilized for such work. Some additional work has been performed in CE immunoassays with heterogeneous methods in which either antibodies or an analog of the analyte is immobilized to a solid support. These heterogeneous methods can be used for the selective isolation of analytes prior to their separation by CE or to remove a given species from a sample/reagent mixture prior to analysis by CE. These CE immunoassays can be used with a variety of detection modes, such as fluorescence, UV/Vis absorbance, chemiluminescence, electrochemical measurements, MS, and surface plasmon resonance.     

An overview of method validation and system suitability aspects in capillary electrophoresis

Summary Although capillary electrophoresis (CE) methods have been included in some regulatory submissions, the formal requirements for validation of such methods are not well-defined or universally understood. This paper provides a general overview of the aspects of method performance which need to be considered during the validation of CE methods particularly emphasising areas of similarity with, and differences between, HPLC and CE. The individual aspects of method performance are reviewed and guidance given, with illustrative literature examples where possible, on how to carry out suitable validation studies. Performance criteria are also provided, wherever possible. In this way, a suggested validation approach for CE methods is presented, reflecting the similarity with that generally adopted for HPLC methods, but accommodating those aspects which are different for, or peculiar to, CE.     

Recent advances in the application of capillary electrophoresis to neuroscience

With fast separation times (seconds to minutes), minimal sample requirements (nanoliters to femtoliters), and excellent mass detection limits (femtomole to zeptomole), capillary electrophoresis (CE) is ideally suited for in vitro and in vivo sampling of neurological samples with a high degree of spatial resolution. Advances in extracellular fluid analysis employing improved microdialysis and push–pull perfusion sampling methodologies has enabled the resolution of neurotransmitters present in limited amounts using CE. Great progress has been made to resolve complex neuropeptides, amino acids, and biogenic amines in tissue and cell cultures. Finally, owing largely to the small volume sampling abilities of CE, investigations of single nerve cells, both invertebrate and mammalian, have been accomplished. These applications of CE to the advancement of neuroscience are presented.     

A high-throughput on-line microdialysis-capillary assay for D-serine.

A high-throughput method is described for the analysis of D-serine and other neurotransmitters in tissue homogenates. Analysis is performed by microdialysis-capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection in a sheath flow detection cell. Sample pretreatment is not required as microdialysis sampling excludes proteins and cell fragments. Primary amines are derivatized on-line with o-phthaldialdehyde (OPA) in the presence of beta-mercaptoethanol followed by on-line CE-LIF analysis. Under the separation conditions described here, D-serine is resolved from L-serine and other primary amines commonly found in biological samples. Each separation requires less than 22 s. Eliminating the need for sample pretreatment and performing the high-speed CE analysis on-line significantly reduces the time required for D-serine analysis when compared with traditional methods. This method has been used to quantify D-serine levels in larval tiger salamander retinal homogenates, as well as dopamine, gamma-amino-n-butyric acid (GABA), glutamate and L-aspartate. D-serine release from an intact retina was also detected.     

Chromatographic determination of pesticides in soil: Current trends in analysis and sample preparation

Soil is a primary sink and reservoir for pesticides pollution and one of the priority objects in terms of pesticides safety guidelines. Pesticides’ analysis in soil is a field of research which is in constant development facing numerous challenges such as the increasing amount and variety of analytes and their combinations, as well as the increasing demand for faster, simpler, more accurate and multiresidue analysis. This review provides the summary of studies on pesticides analysis in soil based on chromatography-coupled methods published between 2015 and 2022. We discuss the shift toward faster, greener, and simpler alternatives to conventional techniques, application of sample preparation and detection methods to targeted and untargeted pesticide analysis, as well as the developments in stereoselective determination of chiral pesticides. The sample preparation methods such as solid-phase extraction, dispersive solid-phase extraction, and derived methods, as well as the recent trends and developments in chromatographic separation of pesticides are covered in this review. For sample preparation, the QuEChERS method is replacing other techniques and has proved to be efficient in both screening and accurate quantification in multiresidue analysis. Shift towards minimal sample preparation is supported by a wider application of highly sensitive and selective separation and detection systems such as LC-MS/MS. The features of different methods of sample preparation and detection are discussed with focus on optimal parameters, advantages, and drawbacks. The optimal parameters of sample preparation methods were summarized based on respective publications, which makes the review a useful tool for method development and further investigations.     

Determination of small phosphorus-containing compounds by capillary electrophoresis

The review focuses on the analysis of small phosphorus-containing compounds by capillary electrophoresis (CE) with different detection modes including UV absorption, laser-induced fluorescence, conductometry, amperometry, atomic spectrometry, and mass spectrometry. Determinations of phosphates, organophosphate, and chemical warfare agents in environmental samples such as water, soil and grains are emphasized. To achieve better sensitivity, high-resolving power, and reproducibility, the optimum separation conditions for various analytes (samples) are different. We compare the merits and demerits of the different detection modes for the detection of the analytes. Although the present methods are successful in many cases, there is still a need to develop high-throughput CE techniques for screening numerous environmental samples and sample stacking techniques in CE for the analysis of trace analytes.