Investigation of drug metabolism using capillary electrophoresis with photodiode array detection and online mass spectrometry equipped with an array detector

Simultaneous determination of ethamsylate, tramadol and lidocaine in human urine by capillary electrophoresis with electrochemiluminescence detection

Ethamsylate, tramadol and lidocaine, partly excreted by the kidney, are generally used as hemostatic, analgesic and local anesthetic in surgery. We developed a simple and sensitive method for their simultaneous monitoring in human urine based on CE coupled with electrochemiluminescence detection by end-column mode. Under optimized conditions the proposed method yielded linear ranges from 5.0 x 10(-8) to 5.0 x 10(-5), 1.0 x 10(-7) to 1.0 x 10(-4) and 1.0 x 10(-7) to 1.0 x 10(-4) M with LODs of 8.0 x 10(-9) M (36 amol), 1.6 x 10(-8) M (72 amol) and 1.0 x 10(-8) M (45 amol) (S/N = 3) for ethamsylate, tramadol and lidocaine, respectively. The RSD for their simultaneous detection at 1.0 x 10(-6) M was 2.1, 2.8 and 3.2% (n = 7), respectively. For practical application an extraction step with ethyl acetate at pH 11 was performed to eliminate the influence of the sample ionic strength. The recoveries of ethamsylate, tramadol and lidocaine at different levels in human urine were between 87 and 95%. This method was used for simultaneous detection of ethamsylate, tramadol and lidocaine in clinic urine samples from two medicated patients. It was valuable in clinical and biochemical laboratories for monitoring these drugs for various purposes.

Capillary electrophoresis-electrospray-mass spectrometry of nucleosides and nucleotides: application to phosphorylation studies of anti-human immunodeficiency virus nucleosides in a human hepatoma cell line

We report the use of capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) for the determination of antiretroviral dideoxynucleosides (ddNs), their nucleotides, and a set of ribonucleosides and ribonucleotides. A CE system for separation of most commonly used antiretroviral ddNs has been developed based on a basic buffer with a volatile electrolyte suitable for ESI-MS detection in an untreated capillary column. Positive and negative ionization modes are investigated and compared for sensitive and stable electrospray performance. A 14-compound mixture of nucleosides and nucleotides is profiled in a single capillary zone electrophoresis separation with a distinct elution order: electroosmotic flow, ddNs, mononucleotides, dinucleotides, and trinucleotides in less than 18 min. The fragmentation pathways of the nucleosides and nucleotides in ESI-MS have been interpreted. Concentration limits of detection are 100 to 200 nM with an injection volume of approximately 10 nL. This technique has been used to detect naturally occurring nucleotides and to study the metabolism of lamivudine (3TC) in the human hepatoma cell line Hep G2. 3TC and its metabolites 3TC-monophosphate, 3TC-diphosphate, and 3TC-triphosphate were detected after 10 h of incubation of 3TC with the cells.

Biomedical and biological mass spectrometry

This review focuses on biological and biomedical mass spectrometry, and covers a selection of publications in this area included in the MEDLINE database for the period 1987-2001. Over the last 15 years, biological and biomedical mass spectrometry has progressed out of all recognition. The development of soft ionization methods, such as electrospray ionization and matrix-assisted laser desorption ionization, has mainly contributed to the remarkable progress, because they can easily produce gas-phase ions of large, polar, and thermally labile biomolecules, such as proteins, peptides, nucleic acids and others. The innovations of ionization methods have led to remarkable progress in mass spectrometric technology and in biochemistry, biotechnology and molecular biology research. In addition, mass spectrometry is one of the powerful and effective technologies for drug discovery and development. It is applicable to studies on structural determination, drug metabolism, including pharmacokinetics and toxicokinetics, and de novo drug discovery by applying post-genomic approarches. In the present review, the innovative soft ionization methods are first discussed along with their features. Also, the characteristics of the mass spectrometers which are active in the biological and biomedical research fields are also described. In addition, examples of the applications of biological and biomedical mass spectrometry are provided.

Experimental designs to investigate capillary electrophoresis-electrospray ionization-mass spectrometry enantioseparation with the partial-filling technique

An experimental design approach is described to evaluate the main electrophoretic parameters involved in the enantioseparation of pharmaceuticals by capillary electrophoresis (CE) coupled to electrospray ionization-mass spectrometry (ESI-MS). For all experiments, the partial-filling technique was applied to avoid the chiral selector entering in the mass spectrometer ion source with a negative effect on the electrospray performance. To carry out enantioseparation, a volatile buffer constituted of 20 mM ammonium acetate at pH 4.0, and a polyvinyl alcohol-coated capillary were used. Methadone was employed as the model compound and three different cyclodextrins (CDs), namely sulfobutyl ether-beta-CD, carboxymethylated-beta-CD and hydroxypropyl-beta-CD, were selected in order to study the countercurrent process. Two different experimental designs were chosen: (i) a full-factorial design to examine the effects and significance of the investigated factors, and (ii) a central composite face-centered design to establish the mathematical model of the selected responses in function of experimental factors. The chiral selector concentration, percentage of the capillary filled with the chiral selector, and drying gas nebulization pressure were three relevant factors taken into consideration. For each CD, the methadone enantiomeric resolution, apparent selectivity, and migration time of the second enantiomer were established as responses. The latter were systematically related to experimental parameters with the help of multiple linear regression. It is noteworthy that the behaviour was different in function of the chiral selector charge. Results revealed that the nebulization pressure involved in the electrospray process and the CD concentration had a significant effect on the enantiomeric resolution, while the effect of the separation zone length was less pronounced. Finally, response surfaces were drawn from the mathematical model and experimental conditions were selected to allow a robust determination of methadone enantiomers by CE-MS.

Capillary electrophoresis-electrospray ionization ion trap mass spectrometry for analysis and confirmation testing of morphine and related compounds in urine

Using an aqueous background electrolyte containing 25 mM ammonium acetate and NH3 (pH 9), CE-tandem MS and CE-triple MS with atmospheric pressure electrospray ionization in the positive ion mode are shown to represent attractive approaches for analysis and confirmation testing of morphine (MOR) and related opioids in human urine. Injection of plain or diluted urine permits monitoring of solutes at concentrations above 2-5 microg/ml. For the recognition of lower concentrations, solute extraction and concentration is required. Liquid-liquid extraction at alkaline pH is shown to be suitable for analysis of free opioids only whereas solid-phase extraction using a mixed-mode polymer phase is demonstrated to permit analysis of both free and glucuronidated opioids. The former sample preparation approach, however, requires about half of the time only. Commencing with 2 ml of urine, reconstitution to provide a sample volume of 0.2 ml and hydrodynamic sample injection, detection limits for free opioids are shown to be on the 100-200 ng/ml drug level. Much improved (ppb) sensitivity is obtained by infusing the extract directly into the source of the MS system. However, solutes that produce equal fragments (such as the two glucuronides of MOR) can thereby not be distinguished. CE-tandem MS and CE-triple MS are demonstrated to be suitable to confirm the presence of MOR, MOR-3-glucuronide, 6-monoacetylmorphine, codeine, codeine-6-glucuronide, dihydrocodeine, methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in a toxicological quality control urine. The same is shown for selected metabolites of codeine and dihydrocodeine in urines collected after administration of pharmaceutical preparations.

Analysis of codeine, dihydrocodeine and their glucuronides in human urine by electrokinetic capillary immunoassays and capillary electrophoresis-ion trap mass spectrometry

Screening for and confirmation of illicit, abused and banned drugs in human urine is a timely topic in which capillary separation techniques play a key role. Capillary electrophoresis (CE) represents the newest technology employed in this field of analysis. Two rapid competitive binding, electrokinetic capillary-based immunoassays are shown to be capable of recognizing the presence, but not the identity, of urinary opioids, namely codeine (COD), codeine-6-glucuronide, dihydrocodeine (DHC), dihydrocodeine-6-glucuronide, morphine (MOR), morphine-3-glucuronide and ethylmorphine (EMOR). In these approaches, aliquots of urine and immunoreagents of a commercial, broadly cross-reacting fluorescence polarization immunoassay for opiates were combined and analyzed by capillary zone electrophoresis or micellar electrokinetic capillary chromatography with laser induced fluorescence detection. With the fluorescent tracer solution employed, the former method is shown to provide simple electropherograms which are characterized by an opioid concentration dependent magnitude of the free tracer peak. In presence of dodecyl sulfate micelles, however, two tracer peaks with equal opioid concentration sensitivity are monitored. These data suggest the presence of two fluorescent tracers which react competitively with the urinary opioids for the binding sites of the antibody. Assay sensitivities for COD and MOR are comparable (10 ng/ml), whereas those for DHC and EMOR are about four-fold lower. Furthermore, glucuronides are shown to react like the corresponding free opioids. Analysis of urines that were collected after administration of 7 mg COD and 25 mg DHC tested positively in both assay formats. The presence of the free and conjugated codeinoids in these urines and their identification was accomplished by capillary electrophoresis-ion trap mass spectrometry (CE-MS). This confirmatory assay is based upon solid-phase extraction using a mixed-mode polymer cartridge followed by CE hyphenated to the LCQ mass spectrometer with electrospray ionization in the positive ion mode. With this technology, MS2 is employed for proper identification of COD (m/z 300.4) and DHC (m/z 302.4) whereas MS3 provides unambiguous identification of the glucuronides of COD (m/z 476.5) and DHC (m/z 478.5) via their fragmentation to COD and DHC, respectively. MSn (n > or = 2) is shown to be capable of properly identifying the urinary codeinoids on the 100-200 ng/ml concentration level.

Hyphenated chromatographic methods for biomaterials

The improvement in hyphenated analytical techniques has significantly widened their applications to the analysis of biomaterials. In this article, we discuss recent advances in applications of hyphenated chromatographic techniques including capillary electrophoresis to the analyses of biological samples. As tools of separation, gas chromatography, high-performance liquid chromatography and capillary electrophoresis are considered with special emphasis on applications utilizing the hyphenation of these methods to mass spectrometry. Moreover, applications using other detection methods such as Fourier transform infrared spectroscopy hyphenated to gas chromatography and photodiode array detector combined with high-performance liquid chromatography or capillary electrophoresis are also discussed. Owing to their high sensitivity, luminescence-based detection systems such as laser-induced fluorescence and chemiluminescence are also included in this review.

Simultaneous stereoselective analysis of tramadol and its main phase I metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry

On-line combination of partial filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the simultaneous enantioseparation of tramadol and its main phase I metabolites. The partial filling technique was efficient at avoiding MS contamination by the chiral selector. Different experimental factors were investigated, including the chiral selector nature and concentration, plug length as well as the separation temperature. The best enantioseparation of the investigated compounds was achieved with a coated polyvinyl alcohol capillary and a 40 mM ammonium acetate buffer, pH 4.0, adding sulfobutyl ether beta-cyclodextrin (2.5 mg/ml) as the chiral selector. The charged cyclodextrin not only allowed enantioseparation of tramadol and its metabolites, but also improved the selectivity of compounds with the same molecular mass. Finally, CE-electrospray ionisation-MS was successfully applied to the stereoselective analysis of tramadol and its main metabolites in plasma after a simple liquid-liquid extraction.

Confirmation testing of amphetamines and designer drugs in human urine by capillary electrophoresis-ion trap mass spectrometry

Monitoring of amphetamines and designer drugs in human urine is a timely topic in clinical toxicology, surveillance of drug substitution, forensic science, drug testing at the workplace, and doping control. Confirmation testing of urinary amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) and 3,4-methylenedioxyamphetamine (MDA) by capillary electrophoresis (CE) combined with atmospheric pressure electrospray ionization and ion trap mass spectrometry (MS) is described. Using an aqueous pH 4.6 buffer composed of ammonium acetate/acetic acid, CE-MS and CE-MS2 provided data that permitted the unambiguous confirmation of these drugs in external quality control urines. Furthermore, other drugs of abuse present in alkaline urinary extracts, including methadone and morphine, could also be monitored. The data presented illustrate that the sensitivity achieved with the benchtop MS is comparable to that observed by CE with UV absorption detection. CE-MS2 is further shown to be capable of identifying comigrating compounds, including the comigration of amphetamine with nicotine.

Trace analysis of haloperidol and its chiral metabolite in plasma by capillary electrophoresis

Capillary zone electrophoresis was developed for the simultaneous determination of haloperidol (HP) and its chiral metabolites [(+)- and (-)- reduced haloperidol, (+)- and (-)-RHP] in human plasma. The method involved the presence of an internal standard and liquid-liquid extraction from plasma. After concentration, the residue from the organic extract was dissolved in aqueous acid for capillary electrophoretic analysis. The background electrolyte was Tris-phosphate buffer with dimethyl-beta-cyclodextrin and PEG 6000. In spiked plasma the quantitative ranges were 40-400 nM for HP and 50-500 nM for (+)-RHP or (-)-RHP. The intra-day and inter-day relative standard deviations (n = 3) were all < 20% for each substance. The detection limits were found to be 15 ng/ml for HP and 30 ng/ml for both enantiomers of RHP (S/N = 3, injection 20 s). All recoveries were > 70%. We investigated the in vivo metabolism of HP in Chinese schizophrenia patients. The results show that (-)-RHP seems to be the only chiral metabolite from these two HP-dosed patients.

Analysis of lipophilic peptides and therapeutic drugs: on-line-nonaqueous capillary electrophoresis-mass spectrometry

This minireview addresses the usefulness of nonaqueous capillary electrophoresis-mass spectrometry (NACE-MS), mainly in the analysis of lipophilic peptides such as gramicidin S and bacitracin, and therapeutic drugs such as pyrazoloacridine, the H2-antagonist mifentidine, tamoxifen, and their metabolites. The beneficial effects of NACE-MS in typical bioanalytical applications are analyzed case by case. A suitable and widely applicable NACE-MS analysis is identified, which is an electrolyte buffer containing ammonium acetate (5-50 mM) and/or acetic acid (up to 100 mM) with varying composition of organic solvents. Either acetonitrile or methanol or a mixture of the two are mostly utilized in the nonaqueous media. Primary considerations in developing NACE-MS are also discussed.

Analyte identification in capillary electrophoretic separation techniques

A review on applications of on-line hyphenation in capillary electrophoresis and capillary electrochromatography for the identification of migrating analytes is presented. There is an urgent need for unambiguous analyte identification by combining spectral information and observed migration times, because the parameters influencing the migration times and separation efficiencies in these separation techniques are not easily controlled, especially when real samples containing unknown interferences have to be analyzed. The spectrometric techniques covered here are ultraviolet and visible radiation (UV/Vis) absorption, fluorescence including fluorescence line-narrowing spectroscopy, Raman spectroscopy, nuclear magnetic resonance and mass spectrometry. Attention is essentially confined to literature reports in which the extra information provided by the detector is really used for identification purposes, especially in real-life samples, while the interfacing as such and analyte detectabilities in standard solutions are only briefly discussed. This article covers an extensive fraction of the literature published on this topic until the beginning of 1998.

Analysis of compounds containing carboxyl groups in biological fluids by capillary electrophoresis

Capillary electrophoresis (CE) is one of the suitable separation techniques used to analyze drugs or metabolites in complicated sample matrices such as plasma, serum and urine. It sometimes requires only a simple process of sample pretreatment, deproteinization, dilution or extraction for biological fluids, otherwise no pretreatment is necessary. Various metabolic disorders concerning the compounds which possess carboxyl groups such as organic acids have been monitored by CE. Drug metabolism in the body can be monitored by the same technique. Recent publications suggest the feasibility of an automated system for diagnosis based on CE technique.

Determination of illicit and/or abused drugs and compounds of forensic interest in biosamples by capillary electrophoretic/electrokinetic methods

The application of capillary electrophoresis (CE) methods in forensic toxicology for the determination of illicit and/or misused drugs in biological samples is reviewed in the present paper. Sample pretreatments and direct injection modes used in CE for analysis of drugs in biological fluids are briefly described. Besides, applications of separation methods based on capillary zone electrophoresis or micellar electrokinetic chromatography with UV absorbance detection to (i) analysis of drugs of abuse, (ii) analysis of other drugs and toxicants of potential forensic interest and (iii) for metabolism studies are reviewed. Also, alternative CE methods are briefly discussed, including capillary isotachophoresis and separation on mixed polymer networks. High sensitivity detection methods used for forensic drug analysis in biological samples are then presented, particularly those based on laser induced fluorescence. A glimpse of the first examples of application of CE-mass spectrometry in forensic toxicology is finally given.

Detection and quantitation of cellularly derived amyloid beta peptides by immunoprecipitation-HPLC-MS

A quantitative method for detection of amyloid beta peptides using immunoprecipitation-HPLC-mass spectrometry (IP-LC-MS) is described. Comparison of IP-LC-MS with sandwich ELISA revealed comparable results in the analysis of A beta 1-40 and A beta 1-42 derived from fetal guinea pig cell media and cell lysates. The use of IP-LC-MS not only allows a quantitative method for A beta 1-40 and A beta 1-42 peptides present in Alzheimer's disease (AD), but allows detection of other A beta peptide species that may also play a role in the onset of AD in humans.

Capillary electrophoresis in clinical toxicology

During the past decade, capillary electrophoresis (CE) emerged as a promising, effective and economic approach for separation of a large variety of substances, including those encountered in clinical toxicology. Reliable and automated CE instruments became commercially available and promoted the exploration of an increasing number of CE methods for illicit and licit drugs in body fluids. The widespread applicability of CE, its enormous separation power and high-sensitivity detection schemes make this technology an attractive and promising tool. This review provides an overview of the key achievements encountered with CE in clinical toxicology, including (i) the rapid assessment of drug intoxications via direct sample injection, (ii) the screening for and determination of illicit and licit drugs in body fluids with drug extraction, drug concentration (stacking) and chiral discrimination, (iii) the application of immunological single and multianalyte assays in the capillary format to the screening for drugs in body fluids, and (iv) drug confirmation by on-column multiwavelength absorbance and fluorescence detection and/or CE coupled to mass spectrometry. With its distinct features (automation, small sample size, minimal sample preparation, requirement of almost no organic solvents, ease of buffer change and method development, speed of analysis, low cost of capillaries and chemicals) CE has a bright future and the twenty-first century will witness the widespread use of a large number of simple and reliable CE based assays for drugs, methods that will be employed in clinical toxicology, therapeutic drug monitoring and forensic science.

Screening for urinary methadone by capillary electrophoretic immunoassays and confirmation by capillary electrophoresis-mass spectrometry

This paper characterizes competitive binding, electrokinetic capillary-based immunoassays for urinary methadone using reagents which were commercialized for a fluorescence polarization immunoassay. After incubation of 25 microL urine with the reactants, a small aliquot of the mixture is applied onto a fused-silica capillary and the unbound fluorescein-labeled methadone tracer is monitored by capillary electrophoresis with on-column laser-induced fluorescence detection. Configurations in presence and absence of micelles were investigated, found to be capable of recognizing urinary methadone concentrations > or = 10 ng/mL, and shown to be suitable for rapid methadone screening of patient urines. Based upon shorter run times and a much better separation of free tracer and antibody-tracer complex, conditions without micelles are preferred. For confirmation analysis of urinary methadone and its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), capillary electrophoresis in a pH 4.6 ammonium acetate-acetic acid buffer was interphased to an atmospheric pressure ionization triple quadrupole mass spectrometry system. Using positive ion electrospray ionization and the tandem mass spectrometry mode with collision-induced dissociation in the collision cell, fragmentation of the two substances was determined. For confirmation via direct urine injection or application of a urinary extract, in-source fragmentation was employed and the first quadrupole was operated in the selected ion monitoring mode by switching between the masses of relevant precursor/product ion sets for methadone (m/z = 310, 265) and EDDP (m/z = 278, 249, 234). This capillary electrophoresis-mass spectrometry approach is shown to permit the confirmation of methadone and EDDP in patient urines that tested positive for methadone using electrokinetic capillary-based immunoassays, a fluorescence polarization immunoassay, and capillary electrophoresis with UV absorption detection.

Metabolism of haloperidol to pyridinium species in patients receiving high doses intravenously: is HPTP an intermediate?

The metabolism of haloperidol (HP) to the potentially neurotoxic pyridinium species, HPP+ and RHPP+, has been demonstrated in humans. In vitro studies in microsomes harvested from various animal species indicate that the tetrahydropyridines, HPTP and RHPTP, could be intermediates in this pathway. However, this has not yet been demonstrated in vivo in humans. In this study, plasma and urine collected from eight critically ill patients treated with high doses of intravenous HP were analyzed for HPTP and RHPTP using HPLC with electrochemical detection. However, neither HPTP nor RHPTP were detected despite plasma concentrations of HP and RHP higher than any previously reported. HPP+ and RHPP+ were both present in the urine in high concentrations and accounted for 1.1 +/- 0.5% and 5.3 +/- 3.6%, respectively, of the administered dose of HP. The apparent elimination half-lives of HPP+ and RHPP+ were 67.3 +/- 11.0 hr and 63.3 +/- 11.6 hr, respectively. The absence of HPTP and RHPTP in plasma and urine suggests that in humans these tetrahydropyridines either are insignificant intermediates in the metabolism of HP in vivo or are present only transiently at their site of formation and are not released into the circulation.

Capillary electrophoresis in clinical and forensic analysis

During the past decade, capillary electrophoresis (CE) emerged as a promising, effective and economic approach for separation of a large variety of substances, including those encountered in clinical and forensic analysis. Reliable and automated CE instruments became commercially available and promoted the exploration of an increasing number of CE methods and fields of application. The widespread applicability of CE, its enormous separation power and high-sensitivity detection schemes make this technology an attractive and promising tool. This review discusses the principles and important aspects of CE-based assays and provides an overview of the key achievements encountered with CE in clinical and forensic analysis, including those associated with the analysis of serum proteins, hemoglobin variants, drugs and nucleic acids. Validated assays, interesting applications and future trends in clinical and forensic analysis are also discussed.

Recent advances in capillary electrophoresis/electrospray/mass spectrometry

Successful on-line interfacing of capillary electrophoresis (CE) with electrospray (ES) mass spectrometry (MS) has progressed substantially in recent years. Of particular note also is the development which has occurred in combining the more advanced capillary-based electromigration separation techniques, such as capillary gel electrophoresis (CGE), capillary isoelectric focusing (CIEF), capillary isotachophoresis (CIT), micellar electrokinetic chromatography (MEKC) and capillary electrochromatography (CEC), with ES/MS. The union of these electromigration schemes with MS detection provides a useful and sensitive analytical tool for the separation, quantitation and identification of biological, therapeutic, environmental and other important classes of chemical analytes. By making optimal use of the characteristics inherent with these separation mechanisms, greatly enhanced MS performance may be obtained. The following review summarizes the significant issues and challenges involved with CE/ES/MS analysis as well as results which have recently been obtained.

Pharmaceutical applications of micelles in chromatography and electrophoresis

This review surveys the use of micelles as separation media in chromatography and electrophoresis. Applications to pharmaceuticals whose molecular masses are relatively small are focused on in this review. In high-performance liquid chromatography (HPLC), chromatography using micelles and reversed-phase stationary phases such as octadecylsilylized silica gel (ODS) columns is known as micellar liquid chromatography (MLC). The main application of MLC to pharmaceutical analysis is the same as in ion-pair chromatography using alkylsulfonate or tetraalkylammonium. In most cases, selectivity is much improved compared with other short alkyl chain ion-pairing agents such as pentanesulfonate or octanesulfonate. Direct plasma/serum injection can be successful in MLC. Separation of small ions is also successful by using gel filtration columns and micellar solutions. In electrophoresis, especially capillary electrophoresis (CE), micelles are used as pseudo-stationary phases in capillary zone electrophoresis (CZE). This mode is called micellar electrokinetic chromatography (MEKC). Most of the drug analysis can be performed by using the MEKC mode because of its wide applicability. Enantiomer separation, separation of amino acids and closely related peptides, separation of very complex mixtures, determination of drugs in biological samples etc. as well as separation of electrically neutral drugs can be successfully achieved by MEKC. Microemulsion electrokinetic chromatography (MEEKC), in which surfactants are also used in forming the microemulsion, is successful for the separation of electrically neutral drugs as in MEKC. This review mainly describes the typical applications of MLC and MEKC for the analysis of pharmaceuticals.

Capillary electrophoresis for pharmacokinetic studies

Different analytical techniques involving capillary electrophoresis for the determination of drugs and metabolites in biological fluids are described. Pharmacokinetic studies carried out using capillary electrophoresis are presented, as well as the in vitro metabolism investigations. The advantages and the limitations of capillary electrophoresis for pharmacokinetic studies are discussed.

Micellar electrokinetic chromatography-mass spectrometry

The combination of micellar electrokinetic chromatography (MEKC) with mass spectrometry (MS) is very attractive for the direct identification of analyte molecules, for the possibility of selectivity enhancement, and for the structure confirmation and analysis in a MS-MS mode. The direct coupling of MEKC with MS can be hazardous due to the effect of nonvolatile MEKC surfactants on MS performance, including the loss of analyte sensitivity and ion source contamination. The possibility of off-line coupling between MEKC and matrix-assisted laser desorption/ionization (MALDI)-MS remains to be investigated. Various approaches for on-line coupling MEKC with electrospray ionization (ESI)-MS, including the use of high-molecular-mass surfactant, an electrospray-chemical ionization (ES-CI) interface, a voltage switching and buffer renewal system, partial-filling micellar plug and anodically migrating micelles, are reviewed and evaluated. The use of an ES-CI interface is most promising for routine operation of on-line MEKC-MS under the influence of nonvolatile salts and surfactants. The use of a high-molecular-mass surfactant allows the formation of a micellar phase at very low surfactant concentrations and avoids the generation of a high level of background ions in the low m/z region. Alternatively, the application of a partial-filling micellar plug and anodically migrating micelles eliminate the introduction of MEKC micelles into the ESI-MS system. It is possible to directly transfer the conventional MEKC separations to partial-filling MEKC-ESI-MS and MEKC-ESI-MS using anodically migrating micelles without any instrument modifications.

High-performance capillary electrophoresis of a fermentation-derived cyclic peptide analog, animal growth promoter

We have developed HPCE methods for the analysis of sulfomycin (trivial name) and related compounds (code name, crude material = U82127 = I), which is an animal growth promoter derived from a fermentation beer. The crude material, I, isolated from the fermentation consisted of more than 40 components which were not completely separated by conventional HPLC. Thus, as a complementary analysis method, we have optimized HPCE conditions for I using various capillaries including uncoated, coated, and packed using various buffers. The optimized HPCE conditions were obtained with an uncoated fused-silica capillary and a buffer that consisted of 30 mM Tris-tricine, 10 mM SDS, 10 mM NaCl and 20% MeOH, pH 8.0. Using these HPCE conditions, we were able to separate the one main component collected from the HPLC effluent into two or three components. In order to identify the main components of the fermentation product, an off-line HPLC-HPCE-MS analysis for I was performed. From the MALDI-TOF-MS results, the separated components collected from HPCE had different molecular masses. Four lots of I samples having different characteristics were also analyzed by HPCE to investigate lot-to-lot differences in peak profiles. The four lots of I were found to have very similar peak profiles. In this paper, I refers to the crude fermentation product and sulfomycin to the purified, major HPLC component of I.

Capillary electrophoresis in pharmaceutical analysis

Capillary electrophoresis (CE) is a separation technique particularly suited to the analysis of pharmaceutical compounds. This review offers a detailed discussion of the four common modes of detection coupled to CE-UV absorption, fluorescence, electrochemical, and mass spectrometry-and gives examples of the use of these methods in pharmaceutical analyses. Sample preparation and pretreatment techniques used for CE separations are described, as well as methods of preconcentration including hydrophobic retention, affinity concentration, sample stacking, and isotachophoresis. The use of affinity CE, chiral CE, and capillary gel electrophoresis for analysis of pharmaceuticals is covered in detail, and recent advances in capillary electrochromatography and CE on a chip are also discussed.

Capillary electrophoresis for drug analysis in body fluids

Capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) represent attractive methods for the determination of drugs and metabolites in body fluids. In CZE, minute (nanoliter) quantities of samples are applied to the beginning of a fused-silica capillary filled with buffer. On application of a high-voltage DC field, charged solutes begin to separate and are swept through the capillary by the combined action of electrophoresis and electroosmotic bulk flow and are on-column detected toward the capillary end. In MECC, the buffer contains charged micelles (e.g., dodecyl sulfate micelles) and both uncharged and charged solutes separate based on differential partitioning between the micelles and the surrounding buffer and, if charged, also by differential charge effects, including electrophoresis. Based on validated MECC drug assays developed in our laboratory, key aspects of measuring drug levels by MECC, including sample preparation, solute detection and identification, quantitation, reproducibility, and quality assurance are discussed. Drug levels determined by MECC are shown to be in good agreement with those obtained by nonisotopic immunoassays and/or high-performance liquid chromatography (HPLC). Using on-column multi-wavelength detection, this technology is also well suited for toxicological drug screening and confirmation and for the exploration of drug metabolism. Compared with HPLC and gas chromatography, capillary electrophoresis has distinct advantages, including automation, small sample size, minimal sample preparation, use of very small amounts of organic solvents and inexpensive chemicals, ease of buffer change and method development, and low cost of capillary columns. Electrokinetic capillary assays are complementary to the widely employed immunoassays. The state of the art and the pros and cons of capillary electrophoresis for the determination of drugs in body fluids are discussed with the goal of encouraging newcomers to start using this emerging analytical methodology.

Micellar electrokinetic chromatography perspectives in drug analysis

Micellar electrokinetic chromatography (MEKC) has become a popular mode among several capillary electromigration techniques. Most drug analyses can be performed by using MEKC because of its wide applicability. Enantiomer separation, separation of closely related peptides and isotopic compounds, separation of very complex mixtures, determination of drugs in the biological samples, etc., can be successfully achieved by MEKC. This review surveys typical applications of MEKC analysis. Recent advances in MEKC, especially with pseudo-stationary phases, are described. Modes of electrokinetic chromatography including MEKC, a separation theory of MEKC and selectivity manipulation in MEKC are also briefly mentioned.

Application of capillary electrophoresis and related techniques to drug metabolism studies

The use of capillary electrophoresis (CE) for the separation of small organic molecules such as pharmaceutical agents and drug/xenobiotic metabolites has become increasingly popular. This has arisen, at least in part, from the complimentary mode of separation afforded by CE when compared to the more mature technique of HPLC. Other qualities of CE include relative ease of method of development, rapid analysis, and low solvent consumption. The recent introduction of a variety of detector systems (including UV diode array, laser-induced fluorescence, conductivity) and the demonstrated coupling of CE to MS have also aided acceptance of this technology. In the present report, we review the role of CE coupled to various detector systems including a mass spectrometer for the characterization of both in vitro and in vivo derived drug metabolite mixtures. Attributes of CE for this application are demonstrated by discussion of metabolism studies of the neuroleptic agent haloperidol. Various aspects of the development and use of CE and CE-MS for the characterization of haloperidol metabolites, including criteria for selection of parameters such as pH, ionic strength, extent of organic modification, and the use of nonaqueous capillary zone electrophoresis are discussed. We also consider potential limitations of CE and CE-MS for drug metabolism research and describe the introduction of membrane preconcentration-CE (mPC-CE) and mPC-CE-MS as a solution that overcomes the rather poor concentration limits of detection of CE methods without compromising the resolution of analytes or separation efficiency of this technique.

Use of mathematically enhanced spectral analysis and spectral contrast techniques for the liquid chromatographic and capillary electrophoretic detection and identification of pharmaceutical compounds

The use of mathematically enhanced ultraviolet/visible (UV/VIS) absorbance spectral analysis and spectral contrast software techniques in high performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (MECC) as an aid for the determination of peak homogeneity, identification, and tracking during method development was investigated. Various structurally similar pharmaceutical compounds, and compounds present as either cis/trans isomers, diastereomers, or enantiomers were used as test compounds to probe the limits of this technique. Two tricyclic antidepressants, nortriptyline and imipramine, were employed to study the effects of HPLC mobile phase composition and pH on the ability to identify and track peaks during method development. It was found that method changes altered the spectral matches used for identification, but not enough to cause incorrect peak identification. It was also shown using HPLC that the cis/trans isomers of doxepin and the diastereomers ephedrine and pseudoephedrine could be distinguished. The mathematically enhanced spectral analysis and spectral contrast software techniques were also employed with MECC. Peaks tracking during method development as pH and the concentration of surfactant changes is shown for a separation of various penicillin type antibiotics. It was shown that during chiral MECC (CMECC) analyses ephedrine/pseudoephedrine diastereomers as well as ephedrine enantiomers could be distinguished. The determination of enantiomers is possible in CMECC since enantiomers are eluted as diastereomeric complexes, as opposed to HPLC where they are eluted in their native state.

Capillary electrophoresis and capillary electrophoresis-mass spectrometry in drug and metabolite analysis

The structural diversity of modern therapeutic agents can lead to labour intensive method development for each drug and the structural characterization of their metabolites. In this work, we show the benefits of the high resolution capabilities of capillary electrophoresis (CE) and demonstrate that nonaqueous CE and on-line CE-mass spectrometry (CE-MS) leads to enhanced resolution and recovery of mixtures containing the prototype H2-antagonist, mifentidine, and putative metabolites. Furthermore, the usefulness of CE-tandem MS (CE-MS/MS) is also demonstrated by the structural characterization of the novel N2-hydroxylamine metabolite of mifentidine.

Clinical and forensic applications of capillary electrophoresis

This survey is aimed at giving the readers a short overview of the present state of the art of clinical and forensic applications of capillary electrophoresis. First, the principles associated with electrokinetic capillary separations and instrumentation, sample preparation and solute quantitation are briefly discussed. This is followed by chapters describing the determination of endogenous and exogenous compounds in body fluids and tissue extracts. Finally, a survey of major achievements including reference to fully developed electrokinetic capillary assays is provided. The paper concludes with a brief outlook.