Capillary electrophoretic determination of S-carboxymethyl-L-cysteine and its major metabolites in human urine: feasibility investigation using on-column detection of non-derivatized solutes in capillaries with minimal electroosmosis

Quantification of fudosteine in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry employing precolumn derivatization with 9-fluorenylmethyl chloroformate

This paper describes a novel method for the sensitive and selective determination of fudosteine in human plasma. The method involves a derivatization step with 9-fluorenylmethyl chloroformate (FMOC-Cl) in borate buffer and detection based on high-performance liquid chromatography-electrospray ionization mass spectrometry (LC/ESI/MS). After acetonitrile-induced protein precipitation of plasma samples, fudosteine was derivatized with FMOC-Cl, then extracted by ethyl acetate, evaporated, reconstituted and injected using an LC/ESI/MS instrument. Separation was achieved using an ODS column and isocratic elution. Excellent linearity was obtained for the entire calibration range from 0.05 to 20 microg/ml. Validation assays of the lower limit of quantification (LLOQ) as well as for the intra- and inter-batch precision and accuracy met the international acceptance criteria for bioanalytical method validation. Using the developed analytical method, fudosteine could be detected for the first time in human plasma with a low limit of detection (LLOD) of 0.03 microg/ml. The proposed method has been successfully applied to study the pharmacokinetics of fudosteine in healthy Chinese volunteers after single and multiple oral administration.

Ion-chromatographic determination of carbocisteine in pharmaceuticals based on non-suppressed conductimetric detection

A novel method for the determination of carbocisteine (S-CMC), a mucolytic and expectorant drug with an acidic amino acid structure, was developed and validated, using non-suppressed ion-chromatographic system with conductimetric detection, and anion or cation exchange columns. Among the various combinations of column type and eluent composition tested, a cation exchange column with a 0.25 mM tri-fluoroacetic acid (TFA) as eluent in isocratic mode at 1.2 ml/min gave the best results. S-CMC was very well separated from all common amino acids (resolution > 2.6). The retention time was 3.5 min and the asymmetry factor 1.1. A linear calibration curve from 17 to 400 microg/ml (r = 0.99994), with a detection limit of 0.14 microg (5.6 microg/ml-25 microl injection volume) and a precision of 1.5% R.S.D. (100 microg/ml, n = 3) was achieved. The proposed method was applied for the determination of S-CMC content in intensely colored commercial formulations (syrups). No interference from excipients was found and the only pretreatment step was the appropriate dilution with the mobile phase. Recovery from standard additions was ranged from 96.0 to 104.9% and precision (R.S.D., n = 3) 1.8-3.6%.

Direct determination of s-carboxymethyl-l-cysteine in syrups by reversed-phase high-performance liquid chromatography

A simple reversed-phase high-performance liquid chromatography method was developed for the determination of s-carboxymethyl-l-cysteine in syrup preparations. The experiments were performed without specific sample pre-treatment. The LC conditions used were acetonitrile-10 mM sodium dihydrogenphosphate buffer, pH 2.0 (1:99, v/v) on a C(18) Inersil column with a flow rate of 1.5 ml/min. Ultraviolet detection was carried out at 240 nm. The method showed excellent linearity (r(2)>0.9998) over the concentration range tested (0.8-25.6 mg/ml) with good precision and accuracy (%R.S.D. 0.7%). Recoveries were good (>99%) with a limit of detection and limit of quantitation of 0.1 and 0.8 mg/ml. Other compositions in the syrup vehicle did not interfere the analysis of s-carboxymethyl-l-cysteine.

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.

New approaches in clinical chemistry: on-line analyte concentration and microreaction capillary electrophoresis for the determination of drugs, metabolic intermediates, and biopolymers in biological fluids

The use of capillary electrophoresis (CE) for clinically relevant assays is attractive since it often presents many advantages over contemporary methods. The small-diameter tubing that holds the separation medium has led to the development of multicapillary instruments, and simultaneous sample analysis. Furthermore, CE is compatible with a wide range of detectors, including UV-Vis, fluorescence, laser-induced fluorescence, electrochemistry, mass spectrometry, radiometric, and more recently nuclear magnetic resonance, and laser-induced circular dichroism systems. Selection of an appropriate detector can yield highly specific analyte detection with good mass sensitivity. Another attractive feature of CE is the low consumption of sample and reagents. However, it is paradoxical that this advantage also leads to severe limitation, namely poor concentration sensitivity. Often high analyte concentrations are required in order to have injection of sufficient material for detection. In this regard, a series of devices that are broadly termed 'analyte concentrators' have been developed for analyte preconcentration on-line with the CE capillary. These devices have been used primarily for non-specific analyte preconcentration using packing material of the C18 type. Alternatively, the use of very specific antibody-containing cartridges and enzyme-immobilized microreactors have been demonstrated. In the current report, we review the likely impact of the technology of capillary electrophoresis and the role of the CE analyte concentrator-microreactor on the analysis of biomolecules, present on complex matrices, in a clinical laboratory. Specific examples of the direct analysis of physiologically-derived fluids and microdialysates are presented, and a personal view of the future of CE in the clinical environment is given.

Micellar electrokinetic capillary chromatography (MECC) of UV-absorbing constituents in normal urine: a chemometric optimisation of the separation

A micellar electrokinetic capillary chromatography (MECC) method when compared to free solution capillary electrophoresis (CZE) was shown to offer improved selectivity and resolution for the separation of UV-absorbing components of human urine. Some of the factors affecting MECC separation e.g. methanol concentration, sodium dodecyl sulphate (SDS) concentration, beta-cyclodextrin (beta-CD) concentration, voltage, pH, temperature and electrolyte additives (urea, beta-CD and Brij 35) were optimised using chemometric techniques. Three-level three-factor (3(3)) factorial designs and simplex optimisation were used to achieve optimised conditions with the goal of obtaining the maximum number of peaks in the shortest possible analysis time. Using a TSP CE2000 instrument with detection from 195-300 nm and fitted with a 75 microns x 44 cm (37 cm effective length) fused silica capillary the final optimum conditions were found to be, an electrolyte consisting of 30 mM sodium tetraborate, pH 10, containing 75 mM SDS and 10 mM beta-CD, 15 degrees C, 20 kV, 4 s hydrodynamic injection of filtered urine. These conditions were capable of separating 70 peaks from a normal human urine pool in less than 12 min. The separation of components in urine using the optimised MECC was simpler, more reproducible, faster and gave better resolution than gradient reversed-phase high performance liquid chromatography.

Direct determination of procainamide and N-acetylprocainamide by capillary zone electrophoresis in pharmaceutical formulations and urine

In this work a new sensitive capillary zone electrophoresis method for the direct determination of procainamide (PA) and N-acetylprocainamide (NAPA) in pharmaceutical formulations and urine samples without any extraction and/or preconcentration steps has been developed. The determination was carried out in a fused-silica capillary of 43.5 cm (35.9 cm length to the detector) x 0.75 micron J.D. Phosphate 0.05 M buffer was used as the background electrolyte and 10 kV separation voltage was applied. The separation of PA and NAPA is possible in a wide range of pH from 1.7 to 9.7. However, in order to avoid the effect of the urine matrix, it is optimal to work at pH 7.7. The determination of PA and NAPA takes less than 5 min while high resolution is achieved. The detection limits obtained, 1.235 micrograms/ml and 0.359 microgram/ml for PA and NAPA respectively, are lower than those for GC method normally reported.

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.

Capillary zone electrophoresis for the rapid screening of banned drugs in sport

Capillary zone electrophoresis was used to analyze some drugs illegally used in sports. The spectroscopic characteristics and electrophoresis migration parameters of diuretics, narcotics-analgesics and beta-blockers were established. Analytical figures of merit including parameters on the precision of migration and limits of detection are discussed. Results for the separation of drugs of different doping families are discussed. An analysis of urine from a patient receiving daily doses of atenolol is presented.

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

The application of capillary electrophoresis (CE) with photodiode array detection (DAD) and on-line CE-mass spectrometry (CE-MS) equipped with a position and time resolved (PATRIC) focal plane detector for analysis of both in vitro and in vivo drug metabolism is demonstrated. Separation of metabolites derived from the neuroleptic drug haloperidol, by CE, using a simple, volatile run buffer containing 50 mM ammonium acetate with 10% methanol and 1% acetic acid is reported. The potential utility of CE-DAD for screening drug metabolite mixtures derived from hepatic microsomal incubations is demonstrated for haloperidol (HAL). Also the potential problems associated with using this technology to screen human urine samples for HAL metabolites is discussed. Furthermore, the usefulness of CE-MS and CE-electrospray ionization skimmer collision induced dissociation-MS (CE-ESI-CID-MS) in identification and structure elucidation of HAL metabolites derived from both a guinea pig hepatic microsomal incubation and urine from a patient treated with 0.5 mg/day of HAL is shown. The utility of such an approach in the general area of clinical pharmacology is also discussed.

Rapid isoelectric focusing of proteins in hydrolytically stable capillaries

Three new types of capillary coatings for capillary isoelectric focusing that avoid siloxane chemistry, resulting in hydrolytically stable coatings, are described and tested: phenyl-silica, acrylamide-reacted vinyl-silica, and pure PTFE. Capillaries of these three types were compared using standard proteins and a biological mixture of proteins similar to what might be encountered in actual use. Of these, the acrylamide-coated capillary produced the highest-quality results. In contrast to capillaries prepared using siloxane reactions, the capillaries described herein exhibited greatly enhanced stability at high pH.

Determination of substituted purines in body fluids by micellar electrokinetic capillary chromatography with direct sample injection

Many substituted purines (theobromine, caffeine, paraxanthine, theophylline and uric acid, as well as other methylated xanthines and uric acids) can easily be separated and analysed in one run using micellar electrokinetic capillary chromatography with a boratephosphate buffer containing 75 mM sodium dodecyl sulphate (pH approximately 9). Serum, saliva and urine samples collected after the self-administration of caffeine and serum samples from patients receiving theophylline or caffeine pharmacotherapy were screened for substituted purines. The data presented show the ease of using on-column multi-wavelength detection for investigating the feasibility of direct sample application, the characterization of sample pretreatment procedures and peak confirmation by comparing absorption spectra. It is shown that the determination of purines in serum and saliva samples, including therapeutic concentrations of caffeine and theophylline, can be accomplished without any sample pretreatment, whereas sample extraction is required for the determination of purines in urine. Quantitative data for the determination of micromolar amounts of theophylline (samples from adult patients) and caffeine (samples from infants born prematurely) in serum samples compared well with data obtained by non-isotopic immunoassays. Micellar electrokinetic capillary chromatography with the direct injection of serum or saliva samples requires only microlitre volumes of sample and several different compounds can be determined within a few minutes.

Use of cyclodextrins for the enantioselective separation of ergot alkaloids by capillary zone electrophoresis

Ergot alkaloid enantiomer derivatives were resolved using capillary zone electrophoresis. The effect of cyclodextrins, added to the background electrolyte, on the migration time and the resolution was studied. Good separation for epimeric ergot alkaloid derivatives was also obtained using phosphate buffer at pH 2.5. Separation was improved by supplementing the background electrolyte with 30 mM of gamma-cyclodextrin. Good resolution of racemic ergot alkaloid derivatives in their enantiomers was achieved in a background electrolyte containing either beta-cyclodextrin or its derivative, or gamma-cyclodextrin.

Determination of thiopental in human serum and plasma by high-performance capillary electrophoresis-micellar electrokinetic chromatography

The quantitation of thiopental in human serum and plasma was investigated using high-performance capillary electrophoresis (HPCE) in a micellar configuration and the results were compared with reversed-phase high-performance liquid chromatography (HPLC). Thiopental and an internal standard (carbamazepine for HPCE and thiamylal for HPLC) were extracted from serum or plasma using pentane and a phosphate buffer (pH 6.4). HPCE analysis took place in a phosphate-borate buffer with 50 mM sodium dodecyl sulphate using an automated instrument and HPLC was performed with a C8 column and a mobile phase of phosphate buffer-acetonitrile (65:35, v/v). HPCE and HPLC data from 66 patient samples compared well based on linear regression analysis. However, estimates obtained with the inclusion of the internal standard were lower than those based on the sample peak only. This example allows the elucidation of the advantages of using HPCE as an assay methodology for the therapeutic monitoring of thiopental and other drugs.

Isotachophoresis of proteins in uncoated open-tubular fused-silica capillaries with a simple approach for column conditioning

The isotachophoretic determination of proteins in uncoated open-tubular fused-silica capillaries of 50 and 75 microns I.C. with on-column multi-wavelength detection is reported. Small amounts of hydroxypropylmethylcellulose added to the leader provide an efficient method of dynamic column conditioning which allows the high-resolution isotachophoretic determination of most proteins to be performed in the presence of an electro-osmotic flow. Different approaches for cationic and anionic analyses are discussed and illustrated with selected examples.

Capillary zone electrophoresis: its applicability and potential in biochemical analysis

Recent developments in capillary zone electrophoresis (CZE) are reviewed, starting with available instrumentation, a description of different operational modes and the most commonly used detection systems. Appropriate attention is paid to CZE-mass spectrometry coupling and coupling of electrophoretic and chromatographic procedures. The possibility of separating chiral molecules is also discussed. Examples of applications concern mainly amino acids, peptides, proteins, nucleic acids and their constituents.

Analysis of barbiturates in human serum and urine by high-performance capillary electrophoresis-micellar electrokinetic capillary chromatography with on-column multi-wavelength detection

The analysis of barbiturates in human serum (or plasma) and urine by high-performance capillary electrophoresis-electrokinetic capillary chromatography with on-column fast-scanning multi-wavelength detection is discussed. The use of a buffer of ca. pH 8 and containing sodium dodecyl sulphate provides a medium suitable for fast and high-resolution separations of barbiturates. Seven barbiturates are characterized by their retention and absorption spectra between 195 and 320 nm. Comparison of these computer-stored data with those of unknown samples is shown to allow the identification of barbiturates in samples of patients undergoing pharmacotherapy and in toxicological urine and serum specimens. Three-dimensional electropherograms provide reliable information on the requirement and suitability of sample pretreatment procedures. With urine, extraction of barbiturates prior to analysis is necessary. With human serum several barbiturates, including phenobarbital, are shown to elute in an interference-free window in front of uric acid and the proteins, allowing these substances to be determined by direct sample injection. The need for multi-wavelength detection over a relatively wide wavelength range as a means of peak confirmation in electrokinetic capillary analyses is demonstrated and limitations of this technique for compounds with similar retention behaviour and absorption spectra are discussed.