Capillary electrophoresis of urinary porphyrins with absorbance and fluorescence detection

Pressure-assisted capillary electrophoresis frontal analysis for faster binding constant determination

Adding external pressure during the process of capillary electrophoresis usually add to the band broadening, especially if the pressure induced flow is significant. The resolution is normally negatively affected in pressure-assisted capillary electrophoresis (PACE). Frontal analysis (FA), however, can potentially benefit from using an external pressure while avoiding the drawbacks in other modes of CE. In this work, possible impact from the external pressure was simulated by COMSOL Multiphysics®. Under a typical CE-FA set-up, it was found that the detected concentrations of analyte will not be significantly affected by an external pressure less than 5 psi. Besides, the measured ligand concentration in PACE-FA was also not affected by common variables (molecular diffusion coefficient (10-8 to 10-11 m2 /s), capillary length etc). To provide an experimental proof, PACE-FA is used to study the binding interactions between hydroxypropyl β-cyclodextrin (HP-β-CD) and small ligand molecules. Taking the HP-β-CD /benzoate pair as an example, the binding constants determined by CE-FA (18.3 ± 0.8 M-1 ) and PACE-FA (16.5 ± 0.5 M-1 ) are found to be similar. Based on the experimental results, it is concluded that PACE-FA can reduce the time of binding analysis while maintaining the accuracy of the measurements.

A Simple Method for Quantification of Five Urinary Porphyrins, Porphobilinogen and 5-Aminolevulinic Acid, Using Liquid Chromatography Tandem Mass Spectrometry

Analysis of porphyrins and 5-aminolevulinic acid (ALA), porphobilinogen (PBG) in physiological liquids is required for diagnosis and follow-up of porphyrias. High performance liquid chromatography (HPLC) and liquid chromatography tandem mass spectrometry (LC-MS) methods with higher specificity and sensitivity have been developed. The major disadvantage of those methods is that they require longer extraction times due to their matrix effects. The present study suggests a simple, fast, sensitive, and specific assay for determination of Coproporphyrin, 5-carboxylporphyrin, 6-carboxylporphyrin, 7-carboxylporphyrin, Uroporphyrin I and ALA, PBG in urine sample by direct injection without sample pre-treatment using LC-MS. For the purposes of the present study LC-MS device was set to multiple reaction monitoring (MRM) and positive ion mode. Porphyrins and ALA, porphobilinogen were characterized by their MS/MS product ion, spectra. ALA, PBG and 5 porphyrins were detected simultaneously. Limit of detection for Coproporphyrin, 5-carboxylporphyrin, 6-carboxylporphyrin, 7-carboxylporphyrin, Uroporphyrin I were 2 nmol/L, where it was 5 μmol/L for ALA and 2 μmol/L for porphobilinogen. The present study suggests that the present method is very effective compared to many other available methods for it does not require pre-treatment, provides simultaneous results of ALA, PBG and 5 porphyrins quantitatively in a shorter span of time, and has suitable sensitivity and selectivity. LC-MS technique was used clinically for the determination of urine porphyrin levels.

Investigation of solvent effects in capillary electrophoresis for the separation of biological porphyrin methyl esters

The effects of organic solvents on the capillary electrophoresis (CE) separation of a number of important biological porphyrin methyl esters - six weakly basic, hydrophobic cyclic tetrapyrroles possessing two and four to eight methyl ester groups around the periphery of the porphyrin ring - were investigated in the mode of micellar electrokinetic chromatography (MEKC), microemulsion electrokinetic chromatography (MEEKC), and nonaqueous CE. In aqueous MEKC, partial separation of the six neutral porphyrin methyl esters was obtained with an organic modifier (acetonitrile) in the concentration range between 20 and 40%, in which sodium dodecyl sulfate (SDS) molecules might be present in the form of SDS micelles and/or SDS micelle-like aggregates. Relatively stable SDS micelles can be formed in nonaqueous MEKC using formamide as the separation medium, but the separation of the target analytes remained unsatisfactory. Improved resolution of all six porphyrin methyl esters was obtained using MEEKC with the running buffer consisting of 0.8% w/w n-heptane (oil phase), 2.25% w/w SDS and 1.0% w/w Brij 35 (mixed surfactant), 6.6% w/w 1-butanol (cosurfactant), and 30% v/v 2-propanol (second cosurfactant), but reproducibility in terms of peak areas for certain porphyrins (especially uroporphyrin I octamethyl ester) was found to be very poor. Best separation performances were achieved with nonaqueous CE separations in which the weakly basic porphyrin methyl esters were protonated under strongly acidic conditions (e.g., using 10 mM perchloric acid) in mixed organic solvents. For example, using a 50:50 mixture of methanol and acetonitrile as the separation medium, baseline separation of all six (positively charged) porphyrin methyl esters can be obtained within 3 min and the average precision (RSD, N = 13) in terms of migration time and peak area were 0.55 and 2.16%, respectively.

Simultaneous determination of six urinary porphyrins using liquid chromatography-tandem mass spectrometry

A liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method without sample pretreatment was developed and validated for determination of porphyrins in samples of canine urine. Acidified urine samples were directly injected into the LC-MS system and a gradient elution program was applied. The mass spectrometer was operated in the multi-reaction monitoring (MRM) mode and six porphyrins were detected with excellent sensitivity and selectivity. The lower limits of quantification were 0.014 nmol/mL for mesoporphyrin IX, coproporphyrin I, 5-carboxylporphyrin, 6-carboxylporphyrin and 7-carboxylporphyrin, and 0.029 nmol/mL for uroporphyrin I. Good ln-quadratic responses of calibration standards over the range 0.01 to 1.0 nmol/mL for mesoporphyrin IX, coproporphyrin I, 5-carboxylporphyrin, 6-carboxylporphyrin and 7-carboxylporphyrin, and 0.02 to 1.0 nmol/mL for uroporphyrin I were demonstrated. This method should be easily adapted through cross-validation for use in determining the effects of chemicals and pharmaceuticals on the urinary excretion profile of porphyrins in preclinical studies with other species, and in assisting the diagnosis of porphyria in clinical studies.

On-line sample preconcentration techniques in micellar electrokinetic chromatography

This review provides an overview as well as a practical understanding of on-line sample concentration techniques in micellar electrokinetic chromatography (MEKC). MEKC as well as other capillary electrophoretic modes suffer from low concentration sensitivity due to minute sample volume and limited optical pathlength for on-capillary photometric detection. Two on-line sample preconcentration techniques, sample stacking and sweeping are known to be effective techniques for enhancement of the concentration sensitivity in MEKC. Sample stacking occurs as ions cross a boundary that separates regions of the high electric field sample zone and the low electric field background solution zone. The difference in migration velocity of pseudostationary phases within the two zones is the key to achieving the focusing effect. Sweeping is defined as the picking and accumulating of analytes by the pseudostationary phase that penetrates the sample zone devoid of pseudostationary phase. In this review, several examples of the sample stacking and sweeping under different experimental conditions are given, besides many references to applications.

Stacking and separation of coproporphyrin isomers by acetonitrile-salt mixtures in micellar electrokinetic chromatography

The effectiveness of the addition of salt and acetonitrile in the sample matrix to induce narrowing of the analyte zones is demonstrated for the first time in micellar electrokinetic chromatography (MEKC). Using coproporphyrin (CP) I and III isomers as test compounds, the use of sodium cholate (SC) as the micelle in the separation buffer and a high concentration of sodium chloride in the aqueous sample solution (without the presence of an organic solvent) were found to provide enhancement in peak heights for both CP I and III, but yielded very poor resolution of these two positional isomers at sample size of 10% capillary volume or larger. With the addition of acetonitrile as the organic solvent in the aqueous sample solution (acetonitrile-salt mixtures), baseline/partial resolution of CP I and III was obtained even at large injection volumes, along with significant increase in peak heights for both isomers. Possible mechanisms responsible for the narrowing of analyte zones are briefly discussed. The effects of experimental parameters, such as concentrations of salt and acetonitrile, on peak heights and resolution of the test compounds were studied. Importantly, the usefulness of the present method was demonstrated for the MEKC determination of endogenous CP I and III present in normal urine samples with good separation and detection performances.

Sample stacking of cationic and anionic analytes in capillary electrophoresis

The behavior of charged species along concentration boundaries in capillary zone electrophoresis (CZE) that was first described in detail by Everaerts et al. in 1979 assured the possibility of concentrating charged solutes inside the capillary. The concentration effect is based on the sudden change in analyte electrophoretic velocity brought about by the difference in the magnitude of the electric field. Furthermore, this on-line method could be the needed solution to the problem of low concentration sensitivity in CZE. Sample stacking, which is now its well known name, has then found valuable use in applying CZE in many fields, especially after the in-depth studies performed in the early 90s by Chien and Burgi. This article reviews the theory and methodological developments of sample stacking developed for charged analytes in CZE and also in electrokinetic chromatography. A table conveying the reported applications especially in the biomedical and environmental fields is given. On top of this, other on-line concentration methods for charged species, namely, sample self-stacking, acetonitrile stacking, sweeping, cation selective exhaustive injection-sweeping, and use of a pH junction, are briefly discussed.

Separation of metalloporphyrins by capillary electrophoresis with UV detection and inductively coupled plasma mass spectrometric detection

Vitamin B12, cobalt protoporphyrin, manganese protoporphyrin, and zinc protoporphyrin were separated using capillary electrophoresis, and a comparison was made between detection with inductively coupled plasma mass spectrometry (ICP-MS) and UV detection. Absolute limits of detection were slightly better with ICP-MS detection than with UV detection, but for both methods absolute detection limits were in the picogram range. The migration times of the analytes decreased by several minutes when ICP MS detection was employed, and this phenomenon was believed to be a result of a "suction effect" that developed when the CE capillary was interfaced to the ICP-MS nebulizer. However, the resolution between species containing the same metal atom was not altered significantly, and the separation was completed in much less time relative to separations performed with UV detection.

New pseudo-stationary phases for electrokinetic capillary chromatography. Complexes between bovine serum albumin and sodium dodecyl sulfate

The complexes formed between a protein (bovine serum albumin, BSA) and a surfactant (sodium dodecyl sulfate, SDS) were studied as separation carriers in electrokinetic chromatography. Selectivities different from those with either SDS or BSA alone in the background electrolyte (BGE) were obtained. Separation performances were demonstrated to be closely related to the type of complex formed, as predicted by the isotherm curve of SDS on BSA. For each composition of background electrolyte, capacity factors and resolutions were calculated. We compared the results with these complexes to electropherograms using BGE containing either BSA or SDS alone. The separation of a mixture of phenols indicate that some compositions of the BSA-SDS complexes are efficient selectors.

Porphyrin-like fluorescence in oral cancer: In vivo fluorescence spectral characterization of lesions by use of a near-ultraviolet excited autofluorescence diagnosis system and separation of fluorescent extracts by capillary electrophoresis

BACKGROUND

Red fluorescence from malignant tumors was observed in experimentally induced rat sarcoma by Policard (1924) and in ulcerated human oral carcinoma by Harris et al. (1987) by examination with ultraviolet (UV) irradiation. The objective of the current study was twofold: to examine in vivo the spectral characteristics of red fluorescence emitted from oral carcinomas and to separate the red fluorescent compounds in these lesions by the capillary electrophoretic (CE) method.

METHODS

In vivo fluorescence spectral characteristics of oral carcinoma were examined by a near-UV excited autofluorescence diagnosis (NEAD) system developed by the authors. Fluorescence spectra of the extract from carcinomas were measured using a spectrofluorometer. CE was used to separate fluorescent compounds from the oral carcinomas.

RESULTS

Of the 78 oral carcinomas examined using the NEAD system, 66 carcinomas (85%), including 2 adenoid cystic carcinomas (ACCs) and 14 recurrent squamous cell carcinomas (SCCs), showed porphyrin-like fluorescence spectra. The CE study was performed on three oral SCCs, two of which contained fluorescent compounds other than protoporphyrin IX and zinc protoporphyrin IX, whereas the other SCCs contained the compounds with the same migration time as protoporphyrin IX.

CONCLUSIONS

Seventy-eight oral carcinomas, including ACCs and recurrent SCCs, were examined using the NEAD system. When exposed to UV light at a wavelength of 410 nm, 85% of the carcinomas showed porphyrin-like fluorescence spectra, whereas the normal mucosa in the oral cavity did not. Porphyrin-like fluorescent compounds were extracted from oral carcinomas and separated by a CE system equipped with a fluorescence detector. The CE data clearly show that compounds vary in each individual carcinoma.

Porphyrin-like fluorescence in oral cancer: In vivo fluorescence spectral characterization of lesions by use of a near-ultraviolet excited autofluorescence diagnosis system and separation of fluorescent extracts by capillary electrophoresis

BACKGROUND

Red fluorescence from malignant tumors was observed in experimentally induced rat sarcoma by Policard (1924) and in ulcerated human oral carcinoma by Harris et al. (1987) by examination with ultraviolet (UV) irradiation. The objective of the current study was twofold: to examine in vivo the spectral characteristics of red fluorescence emitted from oral carcinomas and to separate the red fluorescent compounds in these lesions by the capillary electrophoretic (CE) method.

METHODS

In vivo fluorescence spectral characteristics of oral carcinoma were examined by a near-UV excited autofluorescence diagnosis (NEAD) system developed by the authors. Fluorescence spectra of the extract from carcinomas were measured using a spectrofluorometer. CE was used to separate fluorescent compounds from the oral carcinomas.

RESULTS

Of the 78 oral carcinomas examined using the NEAD system, 66 carcinomas (85%), including 2 adenoid cystic carcinomas (ACCs) and 14 recurrent squamous cell carcinomas (SCCs), showed porphyrin-like fluorescence spectra. The CE study was performed on three oral SCCs, two of which contained fluorescent compounds other than protoporphyrin IX and zinc protoporphyrin IX, whereas the other SCCs contained the compounds with the same migration time as protoporphyrin IX.

CONCLUSIONS

Seventy-eight oral carcinomas, including ACCs and recurrent SCCs, were examined using the NEAD system. When exposed to UV light at a wavelength of 410 nm, 85% of the carcinomas showed porphyrin-like fluorescence spectra, whereas the normal mucosa in the oral cavity did not. Porphyrin-like fluorescent compounds were extracted from oral carcinomas and separated by a CE system equipped with a fluorescence detector. The CE data clearly show that compounds vary in each individual carcinoma.

Bilirubin-human serum albumin interaction monitored by capillary zone electrophoresis

Capillary zone electrophoresis was used to monitor the interaction between bilirubin and human serum albumin. Cord blood serum samples were injected directly into an uncoated fused-silica capillary (30 cm x 50 microns i.d.) and separation was accomplished within 4 min without extensive sample pretreatment. The most suitable running buffer to separate free bilirubin from albumin bound bilirubin was found to contain 1.0 mmol/L EDTA, 5% acetonitrile and 15 mmol/L phosphate with pH adjusted to 8.4. Approximately two bilirubin dianions could be bound per human serum albumin molecule in the cord blood serum. The binding constant was estimated to be 1.1 x 10(5) (L/mol) at 25 degrees C and pH 8.4. The peak area ratio of free bilirubin to total bilirubin can be used to determine the bilirubin binding capacity of cord blood serum for the concentration range of total bilirubin from 204 to 340 mumol/L using 1:5 diluted cord blood seras.

Determination of bupivacaine and three of its metabolites in rat urine by capillary electrophoresis

A capillary electrophoretic (CE) method for the analysis of urinary extracts of the local anesthetic, bupivacaine, and its three main metabolites, desbutylbupivacaine, 3'-hydroxybupivacaine, and 4'-hydroxybupivacaine, in rat urine has been developed. The limits of detection were 0.22 microM for desbutylbupivacaine and bupivacaine, 0.15 microM for 3'-hydroxybupivacaine, and 0.16 microM for 4'-hydroxybupivacaine. The linear range was from 0.7 microM to 16.8 microM for all four compounds. Migration time and peak height reproducibilities, and extraction efficiencies were determined for all four compounds. Peak height reproducibilities (n = 5) for the overall method were improved through the use of prilocaine as an internal standard. Peak height reproducibilities were 5.6% RSD for desbutylbupivacaine and bupivacaine, and 9.9% RSD for 3'-hydroxybupivacaine and 4'-hydroxybupivacaine. Migration time reproducibilities (n = 5) were 2.4% for all compounds. Urine samples were collected from rats administered therapeutic doses of bupivacaine and extracted using a solid-phase extraction method (SPE). Separation of bupivacaine and its metabolites was achieved in 15 min.

Applications of capillary electrophoresis in nephrology

Capillary electrophoresis has recently emerged as a powerful technique for separating components in biological samples. A family of separation methods capable of handling a diverse range of samples has been developed, the sample volumes required are very small and a wide range of specialised detectors can be employed. This review examines some methods with particular application to the analysis of urine and tubular fluid samples and references relevant applications.

Capillary electrophoresis with laser-induced native fluorescence detection for profiling body fluids

Laser-induced native fluorescence detection with a KrF excimer laser (lambda=248 nm) was used to investigate the capillary electrophoretic (CE) profiles of human urine, saliva and serum without the need for sample derivatization. All separations were carried out in sodium phosphate and/or sodium tetraborate buffers at alkaline pH in a 50-microm I.D. capillary. Sodium dodecyl sulfate was added to the buffer for micellar electrokinetic chromatography (MEKC) analysis of human urine. Although inherently a pulsed source, the KrF excimer laser was operated at a high pulse repetition rate of 553, 1001 or 2009 Hz to simulate a continuous wave excitation source. Detection limits were found to vary with pulse rate, as expected, in proportion to average excitation power. The following detection limits (3sigma) were determined in free solution CE: tryptophan, 4 nM; conalbumin, 10 nM; alpha-lactalbumin, 30 nM. Detection limits for indole-based compounds and catecholamine urinary metabolites under MEKC separation conditions were in the range 7-170 nM.

Capillary electrophoretic separation of cationic porphyrins

Cationic porphyrins have a wide variety of uses including those as nucleic acid binding and cleaving agents, as potential pharmacological agents, as electron donor/acceptors in intramolecular electron transfer processes and as analytical reagents. Herein, we report the separation of cationic porphyrins by capillary electrophoresis on fused silica in phosphate buffer at pH 2-5. The porphyrins studied in this work were synthesized from alkylation of the parent tetrapyridylporphyrin (TPyP) to give various pyridinium porphyrins. For example, methylation of TPyP gives a mixture of the mono-, cis-di-, trans-di-, tri- and tetramethylated porphyrins [e.g., 5,10,15,20-tetrakis(N-methyl-4-pyridiniumyl)-21H,23H-p orphyrin, TMPyP(4)]. Capillary electrophoresis on a synthetic mixture showed separation of four of these compounds. Mixtures after alkylation with iodopropionic acid and bromopropylamine were also separated. The cis-di- and trimethylated TMPyP derivatives were separated on a small preparative scale by centrifugal partition chromatography. Capillary electrophoresis was also used to separate metallo TMPyP(4) complexes including those of cobalt, copper, iron, manganese, palladium, tin, vanadium and zinc. The conformational isomers (atropisomers) of 5,10,15,20-tetrakis(N-methyl-2-pyridiniumyl)-21H,23H-p orphyrin, TMPyP(2), were also separated. Net charge, molecular mass and molecular shape all contribute to the differential retention of cationic porphyrins under capillary electrophoresis conditions. Additional factors affecting the separations, including aggregation and protonation of the porphyrins, were probed by evaluating the separation of TMPyP(4) and its butyl and octyl analogs as a function of solution conditions. Cationic porphyrins are difficult to separate using traditional chromatographic methods; capillary electrophoresis and centrifugal partition chromatography provide excellent new techniques for separation of this class of compounds.

Separation of porphyrins by capillary electrophoresis in fused-silica and ethylene vinyl acetate copolymer capillaries with visible absorbance detection

A mixture of 5 porphyrins were separated by capillary electrophoresis. A UV-VIS detector was used to detect the separated components. Separation was performed in 2 types of capillaries, i.e. fused-silica and ethylene vinyl acetate copolymer (EVA) plastic capillaries. The concentration limit of detection (CLOD), mass limit of detection (MLOD), and relative standard deviations (RSD) of migration time and area were investigated. LOD was comparable to that of epi-fluorescence detection. LOD was lower when separation was performed in EVA capillary compared to fused-silica capillary. RSD of migration times of the porphyrins when separated in fused-silica capillary ranges between 0.5 to 1.6% and in EVA capillary ranges between 0.3 to 1.2%. Area RSD in fused-silica capillary ranges between 7 to 20% and in EVA capillary ranges between 4.7 to 12.3%. Urine spiked with porphyrins was also analysed by CE using fused-silica and EVA capillaries. Analysis of urine sample spiked with porphyrins showed that stacking effect of porphyrins was observable only in fused-silica and not in EVA capillary. This led to similar LOD in fused-silica capillary to those for EVA capillary.

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.

Micelles as pseudo-stationary phases in micellar electrokinetic chromatography

This review article describes some general comments on micellar electrokinetic chromatography (MEKC) from the viewpoint of pseudo-stationary phases and presents a compiled list of surfactants used for MEKC, prepared from published papers. We tried to give comments on some typical surfactants from the practical point of view.

Capillary electrophoresis in clinical chemistry

Since its introduction, capillary electrophoresis has diversified, spreading out into different specialized fields covering solutions for almost any analytical questions arising in research laboratories. In the context of clinical chemistry, results must be provided at low costs and in a clinically relevant time frame; however, the attributes which have made capillary electrophoresis such a successful tool in basic research are identical to those attracting clinical laboratories: speed (more efficient, less labor-intensive), low costs (minimal buffer consumption), small sample volume (reduced blood collection volume from patient), increased selectivity (determination of multiple solutes in one run), and versatility (detection of analytes over the wide range of molecular masses and chemical composition). Nevertheless, it should be mentioned that there are still some drawbacks at this stage to be solved in the near future, such as lack of sensitivity for many clinical applications or the constraint to measure in a sequential mode. The aim of this survey is to familiarize clinical chemists, as well as chemists, with a short introduction to capillary electrophoresis, followed by chapters reviewing prominent fields of applications and the latest developments in clinical chemistry.

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.

Analysis of small molecules for clinical diagnosis by capillary electrophoresis

The application of capillary electrophoresis (CE) for the analysis of small molecules in clinical research is growing steadily. Initial studies have dealt with separations of standards or compounds in clean matrices. However, later studies dealt with analysis of those compounds in serum, urine or tissues. Great progress has been accomplished in three areas of clinical interest: organic acids, amino acids and drug analysis. The analysis of these compounds by capillary electrophoresis has several distinct advantages: high resolution, simplicity, versatility and especially low operating costs. In many cases, the sample can be injected directly without complex pretreatment. Most of the described methods have been validated for their precision, linearity and accuracy. In forensic toxicology, the CE has been used for drug identification and as a complementary analytical method.

Determination of thiamphenicol in human plasma by micellar electrokinetic capillary chromatography

A micellar electrokinetic chromatographic method is described for the determination of thiamphenicol in human plasma. The plasma sample was basified by adding K2HPO4 and was then extracted with ethyl acetate. After the solvent was evaporated, the residue was reconstituted in water. Approximately 40 nl of the solution were injected hydrodynamically. The running buffer was 20 mM borate (pH 9.2) containing 40 mM sodium dodecyl sulfate and 10% acetonitrile. The applied voltage was 18 kV and the detector wavelength was set at 195 nm. On-column sample stacking was achieved during the analysis to enhance the sensitivity; the limit of quantitation was 0.1 microg/ml. Linearity was over the range of 0.2 to 10 microg/ml. Recovery was 93.7+/-3.3%, the intra-day precision and accuracy was 99.6+/-2.8%; the inter-day precision and accuracy was 98.4+/-3.4%. The concentration of thiamphenicol in human plasma from eight volunteers was measured after administering thiamphenicol capsules orally.

Micellar electrokinetic chromatography as a fast screening method for the determination of the doping agents furosemide and piretanide in urine

The possibility of using micellar electrokinetic chromatography for the screening of the loop diuretics piretanide and furosemide in urine was studied. A fast and simple method with good repeatability is described. The method was applied to urine samples collected from a healthy volunteer after oral administration of therapeutic doses of each compound. Positive identification in the urine matrix was possible through recording diode array spectra.

Quantitative description of migration behavior of porphyrins based on the dynamic complexation model in a nonaqueous capillary electrophoresis system

The effect of an additive (Brij 35) on the mobilities of a group of porphyrin acids is quantitatively characterized based on a 1:1 dynamic complexation model. Varying additive concentration shifts the equilibrium and changes the viscosity of the background electrolyte. The equilibrium constant, the electrophoretic mobility of the free analyte, and the electrophoretic mobility of the complex are identified as the parameters necessary to describe the analytes' migration behavior. Several statistical methods for obtaining these parameters are discussed. The equilibrium constants and complex mobilities are calculated using three different linear regression methods. The weighted y-reciprocal method was preferred because it gives smaller error, and the data points are evenly distributed along the concentration axis. These values are confirmed using a nonlinear regression to ensure that the proper weighting was used in the linear regression plots. The parameters are then used to predict the apparent mobilities of the analytes over the entire additive concentration range, allowing the optimum separation conditions to be identified. For disc-like molecules, such as porphyrins, the mobility is determined by the orientation of the molecule in an electric field, in addition to their size and charge. The strength of binding between the porphyrins and Brij 35 depends on the number of binding sites and the solvation shell.

Capillary electrophoresis as a clinical tool

Clinical laboratories must produce accurate results for patients with a minimum turn-around time. Automated commercial capillary electrophoresis instrumentation has been available to the clinical laboratory for the past five years. Our laboratory has utilised capillary electrophoresis (CE) to automate serum protein electrophoresis. We have used the technique of CE to produce clinical results for nearly two years. CE methods are also available for the quantitation of haemoglobin variants, by both isoelectric focusing and free solution techniques. Micellar electrokinetic separations by CE have been developed for some specialised drug assays and for B-group vitamin analysis, while gel-filled capillaries have the capability to separate DNA fragments, such as PCR products. Isoenzyme analysis has shown possibilities by CE, but quantitative results are needed to be clinically useful. Analysis of amino acids for newborn screening programs and as an arterial clotting indicator are being developed. The next five years should see a proliferation of clinical laboratory methods using automated CE.

Capillary electrophoretic analyses of drugs in body fluids: sample pretreatment and methods for direct injection of biofluids

A variety of strategies for the analysis of biological samples by capillary electrophoresis (CE) are described, with particular emphasis on the determination of drugs and metabolites. Analytical methods involving extensive sample pretreatment before CE analysis are considered, as well as strategies for directly injecting untreated biofluids. The application in CE of techniques common in liquid chromatography is first described, e.g. protein precipitation, liquid-liquid extraction and solid-phase extraction. On-capillary methods of sample concentration are considered. Approaches to performing CE assays of urine and plasma, without prior sample treatment, are described. The use of both capillary zone electrophoresis and micellar electrokinetic chromatography for direct-injection assays is compared for both urine and plasma analyses, and capillary washing strategies are discussed. Finally, direct-injection microanalyses are 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.

Application of capillary electrophoresis to the simultaneous screening and quantitation of benzodiazepines

Capillary electrophoresis (CE) is an attractive approach for the analysis of drugs in body fluids. We made a simultaneous analysis of nitrazepam, diazepam, estazolam, bromazepam, triazolam and flurazepam using CE with on-column detection at 200 nm. We obtained the best electropherograms under a condition of 5 mM phosphate-borate (pH 8.5) containing 50 mM SDS and 15% methanol. We examined the effect of the sample solvent matrix on the electropherograms obtained, indicating that increasing the methanol content in the sample solvent or the injection volume above a certain threshold limit decreased the resolution. We then focused on application of the CE to the analysis of the drugs in spiked serum, being appropriate for an analysis within 25 min. Linearity, the detection limit, accuracy and reproducibility were established using this method. The calibration curve was linear up to 1 mg/l of serum concentration. The lower limit of detection was 5 pg per injection and 0.025 mg/l of the serum concentration for all the compounds except for flurazepam, for which they were 40 pg/injection and 0.2 mg/l. The detection limits obtained allowed toxicological and pharmacological determinations for nitrazepam, diazepam, estazolam and bromazepam, but not for triazolam and flurazepam. Only toxic blood levels for the latter two benzodiazepines could be quantified by this method. We concluded that the CE could at least be applicable to simultaneous screening for toxic levels of benzodiazepines. We suggest that this technique may offer criminal toxicologists a rapid, simple and adaptable approach for the estimation of many other drugs in body fluids.

Modification of a tunable UV-visible capillary electrophoresis detector for simultaneous absorbance and fluorescence detection: profiling of body fluids for drugs and endogenous compounds

Using fused-silica optical fibres for fluorescence light collection and bandpass filters for selection of emission wavelengths, a capillary electrophoresis detection cell of a conventional, tunable UV-Vis absorbance detector was adapted for simultaneous fluorescence (at selected emission wavelength) and absorbance (at selected excitation wavelength) detection. Detector performance is demonstrated with the monitoring of underivatized fluorescent compounds in body fluids by micellar electrokinetic capillary chromatography with direct sample injection. Compared with UV absorption detection, fluorescence detection is shown to provide increased selectivity and for selected compounds also up to tenfold higher sensitivity. Examples studied include screening for urinary indole derivatives (tryptophan, 5-hydroxytryptophan, tyrosine, 3-indoxyl sulfate and 5-hydroxyindole-3-acetic acid) and catecholamine metabolites (homovanillic acid and vanillylmandelic acid) and the monitoring of naproxen in serum, quinidine in serum and urine and of salicylate and its metabolites in serum and urine.

Comparison of high-performance liquid chromatography and capillary zone electrophoresis in penciclovir biodegradation kinetic studies

High-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE) were used in biodegradation kinetic studies. This paper describes a rapid penciclovir separation using CZE with detection limits comparable to HPLC. The ionic-strength mediated stacking technique was employed while good resolution was maintained. With a shorter analysis time, comparable detection limits and no organic solvent consumption, CZE is a better method for penciclovir biodegradation studies than conventional reversed-phase HPLC (RP-HPLC).

Analysis of basic antimalarial drugs by CZE; Part 2. Validation and application to bioanalysis

This report describes some of the quantitative aspects of the CZE separation of proguanil, chloroquine and their respective metabolites, the separations of which, by CE and MEKC, were reported in Part 1. Results obtained on the precision of migration time and peak areas using the alternative injection methods of vacuum and electrokinetic are described and discussed. The increase in concentration sensitivity using electrokinetic injection with an organic injection solvent reported in Part 1 is confirmed and the resultant limits of detection in urine reported. An assay method for these compounds in urine is described which incorporates a pretreatment stage of solid phase extraction and the main analytical parameters used in the validation of such an assay are reported. The limitation of the sample pretreatment used when applied to matrices of plasma and saliva are reported and discussed in the context of the electrokinetic injection method used.

Mixed polymer networks in the direct analysis of pharmaceuticals in urine by capillary electrophoresis

Two-component polymer mixtures of polyethylene oxide-polydextran have been investigated as unique separation media for capillary electrophoresis. The effects of concentration of the individual polymers and their mixtures on the electroosmotic velocity and electrophoretic mobility of small pharmaceutical compounds were investigated. The molecular masses of polymers, buffer concentrations and percentages of organic solvents and cyclodextrins were varied to explore their effects on the separation process. The plate height against field strength curves were also generated for a better understanding of the kinetic processes involved. The two-component polymer mixtures were found as stable and selective media for the analysis of an anti-ulcer drug famotidine directly in untreated urine.

Investigation of the in vitro metabolism of the H2-antagonist mifentidine by on-line capillary electrophoresis-mass spectrometry using non-aqueous separation conditions

The in vitro metabolism of mifentidine, a prototype second-generation histamine H2-antagonist, is investigated using on-line capillary electrophoresis-mass spectrometry (CE-MS) by analysis of hepatic microsomal incubates. Consideration of the hydrophobicity of this drug and putative metabolites led to the development of a non-aqueous CE separation medium consisting of 5 mM NH4OAc in methanol containing 100 mM acetic acid. Benefits of non-aqueous media in CE-MS studies of small hydrophobic molecules are discussed. In addition, we elucidate both chemical transformations and the in vitro metabolism of mifentidine using guinea pig hepatic microsomes.