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

Structure-Bioactivity Relationships of Methylxanthines: Trying to Make Sense of All the Promises and the Drawbacks

Methylxanthines are a group of phytochemicals derived from the purine base xanthine and obtained from plant secondary metabolism. They are unobtrusively included in daily diet in common products as coffee, tea, energetic drinks, or chocolate. Caffeine is by far the most studied methylxanthine either in animal or epidemiologic studies. Theophylline and theobromine are other relevant methylxanthines also commonly available in the aforementioned sources. There are many disseminated myths about methylxanthines but there is increased scientific knowledge to discuss all the controversy and promise shown by these intriguing phytochemicals. In fact, many beneficial physiologic outcomes have been suggested for methylxanthines in areas as important and diverse as neurodegenerative and respiratory diseases, diabetes or cancer. However, there have always been toxicity concerns with methylxanthine (over)consumption and pharmacologic applications. Herein, we explore the structure-bioactivity relationships to bring light those enumerated effects. The potential shown by methylxanthines in such a wide range of conditions should substantiate many other scientific endeavors that may highlight their adequacy as adjuvant therapy agents and may contribute to the advent of functional foods. Newly designed targeted molecules based on methylxanthine structure may originate more specific and effective outcomes.

Trace analysis of zotepine and its active metabolite in plasma by capillary electrophoresis with solid phase extraction and head-column field-amplified sample stacking

A sensitive high-performance capillary zone electrophoresis (CZE) with head-column field-amplified sample stacking (FASS) in binary system has been developed for the simultaneous determination of zotepine and its active metabolite, norzotepine, in human plasma. The separation of zotepine and norzotepine was performed using a background electrolyte consisting of 50% ethylene glycol-borate buffer (20mM, pH 8.0) solution with 20% methanol as the running buffer and on-column detection at 200 nm. Under the optimal FASS-CZE condition, good separation with high efficiency and short analysis time is achieved. Several parameters affecting the separation and sensitivity of the drug were studied, including sample matrix, pH and concentrations of the borate buffer, ethylene glycol and methanol. Using clozapine as an internal standard, the linear ranges of the method for the determination of zotepine and norzotepine in human plasma were over 3-100 ng/mL; the detection limits of zotepine and norzotepine in plasma were 2 and 1 ng/mL, respectively. A sample pretreatment by means of solid-phase extraction (SPE) with subsequent quantitation by FASS-CZE was used. The application of the proposed method for determination of zotepine and norzotepine in plasma collected after oral administration of 125 mg zotepine in one schizophrenic patient was demonstrated.

Monitoring bronchodilators with direct injection

A procedure was developed for the determination of caffeine and theophylline using a C18 column (5 microm, 250 mm x 4.6 mm) and micellar liquid chromatography using hybrid mobile phases containing sodium dodecyl sulfate (SDS) and propanol, butanol or pentanol as modifiers. Detection was performed with a variable wavelength UV-vis detector at 272 nm. After the application of an interpretative strategy for the selection of the optimimum mobile phase, caffeine and theophylline can be resolved and determined in serum samples by direct injection, using a mobile phase made up of 50 mM SDS-2.5% (v/v) propanol-10 mM KH2PO4, pH 7, with an analysis time below 5 min. Calibration was linear in the range 0.05 to 50 microg mL(-1) with r > 0.999. The statistical evaluation of the method was examined by performing intra-day (n = 6) and inter-day calibration (n = 7) and was found to be satisfactory, with highly accurate and precise results. The proposed method was suitably validated and applied to the determination of caffeine and theophylline in serum samples of patients treated with bronchodilators.

Electroosmotic flow variations caused by the volatility of buffer components: diagnosis and therapy

In order to separate a polar amine pharmaceutical and its potential impurities, a micellar electrokinetic chromatography method was developed. The main compound and 11 other substances were completely separated using a 20 mM Tris buffer, pH 8.0, containing 50 mM sodium dodecylsulfate (SDS) and 24% (v/v) acetonitrile. However, a strong, continuous reduction in the EOF occurred and quantification was not possible. The EOF reproducibility could not be improved by suitable rinsing procedures. Surface effects or interactions did not cause the EOF changes, but the evaporation of acetonitrile was identified as the major source for EOF instability. However, a high concentration of acetonitrile was decisive for selectivity. Thus a reliable protection against the evaporation of this buffer constituent had to be found. Paraffin and various silicon oils were tested as covering film. In order to quickly test buffer systems if the evaporation of electrophoresis solutions is acceptable, an alternative experimental design without doing CE experiments had to be found. Electrical conductivity was chosen as parameter, because it can be determined simply and fast. The buffers under investigation were placed in a 50-ml beaker with a magnetic stirring rod, placed on a magnetic stirrer. The buffer solution was kept in motion at 120 rev./min. The beaker was covered around the measuring head with laboratory film and in addition to this with paraffin or silicon oil. An acetonitrile content up to 10% (v/v) was acceptable if a coverage was used. The various cover liquids had a similar effect. A content of 15% (v/v) already increased the evaporation effect significantly. Higher acetonitrile contents are not acceptable. A buffer similar to the originally transferred method, 20 mM Tris (pH 8.0), 50 mM SDS containing 10% (v/v) acetonitrile as well as 10% (v/v) isopropanol showed an acceptably low evaporation in the conductivity experiments. With this buffer, a stable EOF was also obtained. Conductivity measurements are generally applicable to quickly test buffers that contain organic solvents.

Determination of vancomycin in human serum by micellar electrokinetic capillary chromatography with direct sample injection

BACKGROUND

Vancomycin (VCM) has a bacteriostatic effect on gram-positive bacteria such as the methicillin-resistant Staphylococcus aureus.

METHODS

A new assay for measuring vancomycin concentration by micellar electrokinetic capillary chromatography using direct serum injection was developed. A borate buffer (pH 10.0) containing 100 mmol/l sodium dodecyl sulfate was used as an electrophoresis buffer, and the detection was at 210 nm. The migration time of vancomycin was approximately 7 min.

RESULTS

The linearity was from 0 to 100 microg/ml, with the limit of detection of 1.0 microg/ml (S/N=3). The within-run CV was 3.99-5.53%, and the recovery rate was 91-103% for a concentration range of 6.5-45.5 microg/ml. The between-day CV was 6.76% at 22.2 microg/ml. There was no interference from 32 other antibiotics. The correlation coefficient between the assay and fluorescence polarization immunoassay and direct injection HPLC was 0.982 and 0.985, respectively. The assay required no sample preparation of serum and used only microquantities of an electrophoresis buffer and samples.

CONCLUSIONS

This assay is cost-effective and suitable for routine clinical use.

Determination of carbamazepine and carbamazepine-10,11-epoxide in human serum and plasma by micellar electrokinetic capillary chromatography in the absence of electroosmosis

Therapeutic drug monitoring of carbamazepine (CBZ), a widely used antiepileptic drug, is required for optimization of pharmacotherapy with this drug and for assessment of the patient's compliance to therapy. The suitability of employing micellar electrokinetic capillary chromatography (MEKC) in the absence of electroosmosis for the determination of CBZ and its main metabolite carbamazepine-10,11-epoxide (CBZE) in extracts of human serum and plasma is reported. Using micelles formed by dodecyl sulfate, analyses performed in untreated fused-silica capillaries at acidic pH and in commercially available coated capillaries under application of reversed polarity are compared. Uncoated and polyvinyl alcohol coated capillaries proved to be unsuitable for this purpose, whereas capillaries coated with linear polyacrylamide and N-acryloylaminoethoxyethanol and operated at pH 7.6 are shown to provide high-quality and reliable data on a short time scale. Assay performance is discussed via statistical analysis of the data produced from a set of quality control sera that contain up to 14 different drugs and via analysis of patient samples. Intraday and interday imprecision data for concentrations between 4.0 and 84 microM are demonstrated to be < 10%. Run times are shown to be < 50% compared to those observed in conventional MEKC at alkaline pH (i.e., in the presence of electroosmosis).

Chiral separation of amino acids in biological fluids by micellar electrokinetic chromatography with laser-induced fluorescence detection

A method is presented for the chiral analysis of amino acids in biological fluids using micellar electrokinetic chromatography (MEKC) and laser-induced fluorescence (LIF). The amino acids are derivatized with the chiral reagent (+/-)-1-(9-anthryl)-2-propyl chloroformate (APOC) and separated using a mixed micellar separation system. No tedious pre-purification of samples is required. The excellent separation efficiency and good detection capabilities of the MEKC-LIF system are exemplified in the analysis of urine and cerebrospinal fluid. This is the first time MEKC has been reported for chiral analysis of amino acids in biological fluids. The amino acids D-alanine, D-glutamine, and D-aspartic acid have been observed in cerebrospinal fluid, and D-alanine and D-glutamic acid in urine. To the best of our knowledge no measurements of either D-alanine in cerebrospinal fluid or D-glutamic acid in urine have been presented in the literature before.

Capillary electrophoresis as a versatile tool for the bioanalysis of drugs--a review

This review article presents an overview of current research on the use of capillary electrophoretic techniques for the analysis of drugs in biological matrices. The principles of capillary electrophoresis and its various separation and detection modes are briefly discussed. Sample pretreatment methods which have been used for clean-up and concentration are discussed. Finally, an extensive overview of bioanalytical applications is presented. The bioanalyses of more than 200 drugs have been summarised, including the applied sample pretreatment methods and the achieved detection limits.

Micellar electrokinetic capillary chromatography as a powerful tool for pharmacological investigations without sample pretreatment: a precise technique providing cost advantages and limits of detection to the low nanomolar range

A number of pharmaceuticals (e.g., acetaminophen, salicylic acid, sulfamethoxazole, theophylline, tolbutamide and trimethoprim) have been determined in human plasma by micellar electrokinetic chromatography (MEKC), without sample pretreatment, using underivatized fused-silica capillaries. The total analysis time was only 10 min. A sodium dodecyl sulfate (SDS)-containing borate buffer (60 mM with 200 mM SDS) at pH 10 was used. Between runs, proteins adsorbed to the capillary wall are removed by rinsing with SDS buffer and either acetonitrile (e.g., 50% v/v) or isopropanol (e.g., 10% v/v). Other rinsing procedures are discussed (salts, enzyme-containing solutions, organic solvents, sodium hydroxide, hydrofluoric acid). The separation system is tested in a concentration range between 10 ng/mL and 100 microg/mL; a detection limit of about 20 ng/mL can readily be obtained. The sensitivity was substantially improved using isopropanol as buffer additive. A day-to-day precision for relative peak areas of 1-2% relative standard deviation (RSD, n > 40) was reached in the upper concentration range. Under repeatability conditions, these values could also be obtained for low microg/mL concentrations. Thus, not only drug monitoring but also pharmacokinetic investigations from blood plasma become possible without further sample pretreatment.

Micellar electrokinetic capillary chromatography method for direct determination of glucuronides of entacapone and its (Z)-isomer in human urine

This paper describes the validation of a micellar electrokinetic capillary chromatography method for the direct determination of the 3-O-glucuronides of entacapone and its (Z)-isomer, the main urinary metabolites of entacapone in humans. Entacapone is a novel drug which, as a potent inhibitor of catechol-O-methyltransferase (COMT), is used as an adjunct in the standard therapy of Parkinson's disease. The 3-O-glucuronide of another COMT inhibitor, nitecapone, was used as internal standard (I.S.). The validation experiments were performed by using spiked urine samples that were extracted with Sep-Pak C18 cartridges before analysis. Determinations were carried out in a buffer of pH 7.0 containing 25 mM of phosphate, 50 mM of borate and 20 mM of sodium dodecyl sulfate, and by applying 15 kV over a 67 cm (60 cm to the detector) x 75 microns fused-silica capillary. UV detection was at 335 nm. The validity of the method was assessed by investigating the identity of the analytes, selectivity, limit of quantitation, linearity, within-day precision, extraction recovery, between-day precision and accuracy, electroosmotic flow stability and analyte stability. The method proved to be reproducible, sufficiently selective and accurate. Extraction recoveries of the analytes were > 94%. The limit of quantitation (LOQ) was 2 micrograms/ml and the assay was linear in the range 2-150 micrograms/ml with correlation coefficients better than 0.999 for both glucuronides. The repeatability of the method, expressed as the ratio of corrected peak area of the analytes to that of I.S., gave RSD values of < 5% even at the LOQ. Between-day precision (RSD) was < 7.5% for both glucuronides at 7.5 micrograms/ml. Determination of the glucuronide concentrations in urine samples of 34 patients treated with entacapone either orally (200 mg) or intravenously (25 mg) showed the method to be suitable for monitoring the concentrations of the glucuronide of entacapone after both oral and intravenous administration and those of the glucuronide of its (Z)-isomer after oral administration. The limited long term stability of the system requires, however, frequent recalibration in applications involving long sample series.

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.

Capillary electrophoresis for therapeutic drug monitoring

Therapeutic drug monitoring is commonly used in both the ambulatory and hospital patient care settings. Routine measurement of concentrations of therapeutic agents in biological fluids is critical for certain drugs to maintain therapeutic benefit with minimizing drug-associated toxicities. Many analytical laboratory techniques are currently available to measure drug concentrations in biological samples. Recently there has been an increased interest in the use of capillary electrophoresis (CE) for measuring concentrations of therapeutic drugs in patient samples. However, while there are numerous reports of CE being used to measure drug concentrations in solution and pharmaceutical dosage forms, there are relatively few reports of the use of CE for measuring therapeutic agents in patient samples. The purpose of this paper is to provide an overview of methods currently used to measure therapeutic drugs in patient samples along with possible future trends for the use of CE in therapeutic drug monitoring.

Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications

This review is in support of the development of selective, reproducible and validated capillary electrophoretis (CE) methods. Focusing on pharmaceutical and biological applications, the successful use of CE is demonstrated by more than 800 references, mainly from 1994 until 1998. Approximately 80 recent reviews have been catalogued. These articles sum up the existing strategies for method development in CE, especially in the search for generally accepted concepts, but also looking for new, promising reagents and ideas. General strategies for method development were derived not only with regard to selectivity and efficiency, but also with regard to precision, short analysis time, limit of detection, sample pretreatment requirements and validation. Standard buffer recipes, surfactants used in micellar electrokinetic capillary chromatography (MEKC), chiral selectors, useful buffer additives, polymeric separation media, electroosmotic flow (EOF) modifiers, dynamic and permanent coatings, actions to deal with complex matrices and aspects of validation are collected in 20 tables. Detailed schemes for the development of MEKC methods and chiral separations, for optimizing separation efficiency, means of troubleshooting, and other important information for key decisions during method development are given in 19 diagrams. Method development for peptide and protein separations, possibilities to influence the EOF and how to stabilize it, as well as indirect detection are considered in special sections.

A literature assessment of sample pretreatments and limits of detection for capillary electrophoresis of drugs in biological fluids and practical investigation with some antimalarials in plasma

A literature survey on published reports of the determination of drugs in biological fluids shows that all methods of sample pretreatment have been used and that the limits of detection achieved vary widely, ranging from low ngcm(-3) to microgcm(-3). The most widely used injection method was hydrodynamic and, in the majority of cases, whenever low detection limits were achieved, this was a result of preconcentration during the sample pretreatment. Only a small proportion of the reported methods employed electrokinetic injection and utilised the field amplified sample injection (FASI) techniques. An experimental investigation of the alternative hydrodynamic and electrokinetic injection methods for a small set of antimalarial drugs is reported. It was found that electrokinetic injection with FASI from an acetonitrile-water matrix produced dramatic improvements in detection limits. This improvement could not, however, be achieved when the drugs were in plasma using protein precipitation, liquid-liquid extraction or solid phase extraction pretreatment methods. This highlights the importance of sample pretreatment in utilising the potential sensitivity of capillary electrophoresis with electrokinetic injection.

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.

Therapeutic drug monitoring by capillary electrophoresis

Because of the ease of analysis and the high resolution, drug analysis is becoming the best example for the application of capillary electrophoresis. Therapeutic drug monitoring is a specialized area of drug analysis performed in clinical laboratories for patient care. CE offers high resolution and speed with the low operating costs needed in patient care. However, CE has a few limitations, mainly poor detection limits and precision. Simple methods of stacking, which enhance drug detection to overcome the poor sensitivity of CE are stressed. Serum has a unique matrix with a high content of proteins and salts which can have adverse effects on separation by CE. For successful analysis, special maneuvers are employed to decrease these matrix effects. Studies that have addressed the improvement of the precision of CE are summarized. CE offers the possibility of bringing chiral separations into the routine arena.

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.

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.

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.

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 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.

Determination of pharmaceuticals in plasma by capillary electrophoresis without sample pretreatment reproducibility, limit of quantitation and limit of detection

Pharmaceuticals in human plasma are determined on underivatized fused-silica capillaries by micellar electrokinetic capillary chromatography (MEKC) without sample pretreatment. Our best method to date uses as running buffer a sodium dodecyl sulfate (SDS) containing borate buffer (60 mM with 200 mM SDS) at pH 10. Between runs, proteins adsorbed to the capillary wall are removed by an acetonitrile and SDS-buffer rinsing regimen (50% v/v each). A day-to-day precision for relative peak areas of about 2% relative standard deviation (RSD; n > 40) has been reached. Different rinsing approaches are discussed (salts, enzyme-containing solutions, organic solvents, hydrofluoric acid). The separation system is tested in a concentration range between approximately 100 mg/L-10 mg/L. Correlations between the limit of quantitation, the limit of detection and the signal/noise are discussed. The applicability of the system is demonstrated for the pharmaceuticals acetaminophen, salicylic acid, sulfamethoxazole, tolbutamide, and trimethoprim.

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.

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.

Identification and quantitative determination of uric acid in human urine and plasma by capillary electrophoresis with amperometric detection

Application of capillary zone electrophoresis with electrochemical detection to the identification and quantitative determination of uric acid in human urine as well as plasma is described. This work was carried out in a 30 cm x 25 microm I.D. fused-silica capillary with tricine buffer and a carbon fiber bundle was employed as a working electrode, the working voltage in amperometric detection was set at +0.80 V (vs. SCE). The sample constituent is identified by stopped flow-linear sweep voltammetry. Under optimal conditions, a lower detection limit of 0.48 fmol was obtained for uric acid.

Elimination of theophylline metabolites in healthy adults

The metabolism of theophylline (TP) (540 mg per os) was determined by measuring plasma and saliva concentrations of TP and its metabolites, 0-24 h after loading, and urinary excretion 0-48 h after loading. TP and its five metabolites were separated and quantified by combining high-performance liquid chromatography and capillary electrophoresis. In addition to TP, 1,3-U, 3-X and 1-U were consistently found in plasma and saliva. The area under the plasma concentration-time curve (AUC) showed that TP accounted for 91 +/- 4% (mean +/- SD) of the total AUC in plasma with 1,3-U accounting for 3.1 +/- 1.4%, 3-X for 3.4 +/- 1.8% and 1-U for 2.5 +/- 1.5%. The urine analyses showed that unchanged TP accounted for 19 +/- 5% of total excretion, the remainder being 1, 3-dimethyluric acid (1,3-U, 41 +/- 6%), 1-methylxanthine (1-X, 2 +/- 0.8%), 1-methyluric acid (1-U, 26 +/- 6%), 3-methylxanthine (3-X, 11 +/- 3%) and 3-methyluric acid (3-U, 1 +/- 0.3%). Highest excretion rates were observed for 1,3-U (70 +/- 29 mumol/h), 1-U (40 +/- 26 mumol/h) and 3-X (20 +/- 15 mumol/h) 6-9 h after TP ingestion suggesting the high excretion of 1,3-U, 1-U and 3-X by the kidneys. The highest excretion rate of TP (50 +/- 8 mumol/h) occurring at 0-6 h after the load and rapidly declining thereafter, indicated the lower excretion of TP compared with its metabolites. N3-demethylation of TP accounted for 34 +/- 6% of the urinary metabolites, N1-demethylation of TP for 15 +/- 3% and C8-oxidation of TP for 51 +/- 9%. C8-oxidation of 1-X and 3-X was 93 +/- 4%, and 9 +/- 4%, respectively, of the excreted amount of monomethylxanthine plus formed monomethylurate. Since the extent of all metabolic reactions remained constant during the load, it is suggested that TP is metabolized by hepatic reactions that occurred simultaneously and not sequentially.

Determination of creatinine and other uremic toxins in human blood sera with micellar electrokinetic capillary electrophoresis

We have been interested in the clinical use of capillary electrophoresis (CE) to monitor low-molecular-mass uremic toxins in body fluids. Creatinine, an important clinical marker for renal failure, is zwitterionic over a fairly wide pH range (pH 5-9) and can not be resolved from neutral components using free solution CE under these conditions. We report here a micellar electrokinetic capillary chromatography method using an sodium dodecyl sulfate-borate buffer system at pH 9.0 to determine creatinine levels in human serum. This method, performed on deproteinized sera, is also suitable for determining multiple ionic components. Moreover, this method compares favorably with an enzymatic method for creatinine performed in a clinical laboratory and thus appears to be a promising method in terms of potential clinical use.

Determination of caffeine and its metabolites by micellar electrokinetic capillary electrophoresis

The determination of caffeine and its analogues is important for a wide variety of analyses and is performed in an assortment of matrices ranging from food to clinical samples. While reversed-phase HPLC has become the standard analysis protocol in most laboratories, capillary electrophoresis has the advantages of higher separation efficiency and shorter separation time. The micellar capillary electrophoresis (MECC) separation of caffeine and its metabolites, theobromine, paraxanthine, theophylline and 1,3,7-trimethyluric acid was investigated using sodium dodecyl sulphate (SDS) as the micellar phase. The effects of pH, micelle concentration, buffer concentration, ionic strength, buffer salts, applied voltage and injection time were studied to select the optimum conditions for the determination of caffeine and its four analogues in drugs, foods and body fluids. Caffeine and its three analogues were resolved within 120 s with detection limits less than 1 microgram/ml. Samples could be analyzed utilizing direct injection with satisfactory resolution and reproducibility.

Determination of fluconazole in human plasma by micellar electrokinetic capillary chromatography with detection at 190 nm

The determination of fluconazole (Diflucan) in human plasma by micellar electrokinetic capillary chromatography (MECC) with on-column UV absorption detection at 190 nm from primary, deproteinized and extracted plasma samples is discussed. Direct injection of plain plasma or of the supernatant after protein precipitation with acetonitrile is shown to permit the determination of fluconazole drug levels of > 5 micrograms/ml only. With liquid-liquid extraction employing dichloromethane, the detection limit is about 1 microgram/ml. After extraction using disposable solid-phase C18 cartridges and 1 ml of plasma, however, drug levels as low as 100 ng/ml can be determined unambiguously. Calibration graphs between 0.125-25.0 micrograms/ml (seven data points) are shown to be linear, with a regression coefficient r > 0.999. for fluconazole plasma levels of 5 micrograms/ml, intra-day and inter-day imprecisions (n = 10) are about 2 and 5%, respectively. Using the same solid-phase extraction procedure, 44 fluconazole plasma levels that were determined by MECC are shown to agree well with those obtained by HPLC and elucidated pharmacokinetic data compare well with those found in the literature. The advantages of using MECC instead of HPLC for the determination of fluconazole plasma levels and pharmacokinetics are the high resolution efficiency, low-cost capillary columns and the small consumption of inexpensive and environmentally friendly chemicals.

Laser induced resonance energy transfer--a novel approach towards achieving high sensitivity in capillary electrophoresis. I. Clinical diagnostic application

Most of the procedures currently performed by capillary zone electrophoresis (CZE) with laser induced fluorescence detection requires prior derivatization. This increases cost, the turn-around-time and chances of extraneous contaminations. CZE with laser induced resonance energy transfer is demonstrated as a viable alternative for detecting non-fluorescent compounds with no prior derivatization. The feasibility of this approach is demonstrated by separating and directly detecting salicylic acid (2,4-dihydroxybenzoic acid), gentisic acid (o-methoxybenzoic acid), salicyluric acid (o-hydroxyhippuric acid) and 4-aminosalicylic acid in urine. The detection of salicylate in serum is also shown. The method is highly sensitive with detection limits in the 1.10(-7) M range. Importantly it requires no prior preconcentration or sample preparation and can be used with complex sample matrices such as serum and urine.

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.

Elimination of theobromine metabolites in healthy adults

The metabolism of theobromine (TB) (500 mg per os) was determined by measuring plasma and saliva concentrations of TB and its metabolites 0-24 h after the load, and urinary excretion 0-48 h after the load. TB and its six metabolites were separated and quantified by combining high performance liquid chromatography and capillary electrophoresis. The urine analyses showed that unchanged TB accounted for 21 +/- 4% (mean +/- SD) of total excretion, the remainder being 7-methylxanthine (7-X, 36 +/- 5%), 3-methylxanthine (3-X, 21 +/- 4%), 6-amino-5[N-methylformylamino]-1-methyluracil (6-AMMU, 11 +/- 4%), 7-methyluric acid (7-U, 10 +/- 2%), 3,7-dimethyluric acid (3,7-U, 1.3 +/- 0.6%) and 3-methyluric acid (3-U, 0.5 +/- 0.4%). In addition to TB, 7-X and 3-X were consistently found in plasma and saliva; 6-AMMU and 7-U were found in plasma and saliva at concentrations < or = 2 mumol l-1 and 0.2 mumol l-1, respectively. TB concentrations in plasma and saliva were similar, whereas the saliva concentrations for 7-X and 3-X were found to be 63 +/- 17% of the plasma concentrations for 7-X and 74 +/- 13% for 3-X, respectively. The high urinary-to-plasma concentration ratio of 7-U (200-300) suggests high excretion of 7-U by the kidneys. Excretion of 7-X, 3-X and 6-AMMU was also high (urinary-to-plasma concentration ratio 45-150), whereas the excretion of TB was significantly lower than its metabolites (urinary-to-plasma concentration ratio 4-6). N3-demethylation of TB accounted for 58 +/- 7% of the urinary metabolites, N7-demethylation for 27 +/- 6%, C8-oxidation of 7-X for 22 +/- 4%, C8-oxidation of 3-X for 2 +/- 2% and formation of 6-AMMU for 13 +/- 4%. The ratio of N3- to N7-demethylation of TB remained constant during the load, but the large interindividual variation observed in ratio makes it unsuitable as a function test for evaluation of liver disease.

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.

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.