Capillary electrophoresis as a clinical tool. Determination of organic anions in normal and uremic serum using photodiode-array detection

Determination of uric acid in plasma and allantoic fluid of chicken embryos by capillary electrophoresis

Capillary electrophoresis with diode array detection (DAD) was used to determine uric acid (UA) in chicken plasma and the allantoic fluid of chicken embryos. Complete separation of uric and ascorbic acids was attained in less than 10 min in the optimized BGE containing 60 mM MES + 30 mM Tris + 0.001% (w/v) polybrene (pH 6.1). The limit of UA detection (0.2 mg/L) was found to be low enough for sensitive analysis of native plasma and allantoic fluid samples. Range of linearity (1-200 mg/L), repeatability for peak area (CV <4.1%) and migration time (CV < 2.5%), as well as recovery of UA from biological samples (97-100%), were found to be satisfactory. The method was applied to detect the elevated UA concentrations (hyperuricemia) in chicken embryos with induced unilateral renal agenesis. CE/DAD analysis of the chicken plasma can be carried out with a relatively small volume of samples (1 microL).

Simultaneous determination of low-molecular-weight organic acids and chlorinated acid herbicides in environmental water by a portable CE system with contactless conductivity detection

This report describes a method to simultaneously determine 11 low-molecular-weight (LMW) organic acids and 16 chlorinated acid herbicides within a single run by a portable CE system with contactless conductivity detection (CCD) in a poly(vinyl alcohol) (PVA)-coated capillary. Under the optimized condition, the LODs of CE-CCD ranged from 0.056 to 0.270 ppm, which were better than for indirect UV (IUV) detection of the 11 LMW organic acids or UV detection of the 16 chlorinated acid herbicides. Combined with an on-line field-amplified sample stacking (FASS) procedure, sensitivity enhancement of 632- to 1078-fold was achieved, with satisfactory reproducibility (RSDs of migration times less than 2.2%, and RSDs of peak areas less than 5.1%). The FASS-CE-CCD method was successfully applied to determine the two groups of acidic pollutants in two kinds of environmental water samples. The portable CE-CCD system shows advantages such as simplicity, cost effectiveness, and miniaturization. Therefore, the method presented in this report has great potential for onsite analysis of various pollutants at the trace level.

Analysis of carboxylic acids in biological fluids by capillary electrophoresis

This review article addresses the different capillary electrophoretic methods that are being used for the study of both short-chain organic acids (including anionic catecholamine metabolites) and fatty acids in biological samples. This work intends to provide an updated overview (including works published until November 2004) on the recent methodological developments and applications of such procedures together with their main advantages and drawbacks. Moreover, the usefulness of CE analysis of organic acids to study and/or monitor different diseases such as diabetes, new-borns diseases or metabolism disorders is examined. The use of microchip devices and CE-MS couplings for organic acid analysis is also discussed.

Differential metabolic effects on mitochondria by silica hydride using capillary electrophoresis

Working as an extension of a newly developed method for a capillary electrophoretic analysis of purine nucleotides, nucleosides, bases, and catabolism, an assay of the differential metabolic properties by a novel organosiliceous anionic hydride compound, silica hydride, was evaluated with Chinese hamster ovary mitochondria using a 50-microm poly(acryloylaminopropanol)-coated, fused-silica capillary. The results of this organellar differential analysis indicate a correlation of increased redox pair of NADH to NAD(+) ratios by two times and an increase in ATP levels in the assayed mitochondria by six times. Glucose levels in the organelles were half of the original values. This study validates the electrophoretic method utilizing live organelle fractions for differential metabolic analysis and additionally illustrates some of the emerging novel properties of silica hydride. As confirmation of the results obtained in this assay, additional methods of standard protocol were used to monitor the mitochondrial metabolic activity.

Evaluation of diabetes-related short-chain organic acids in rat plasma by capillary electrophoresis

A capillary zone electrophoresis method was optimised to analyse low-molecular-mass organic acids for the purpose of monitoring diabetes in rat plasma. The method included acetoacetic, 2-hydroxybutyric, lactic and uric acids. A variation in the background electrolyte allowed us to measure pyruvic acid in the same sample. Conditions have been optimised for measuring a large number of plasma samples corresponding to control and diabetic rats. Samples were mixed with acetonitrile (1:1, v/v) to precipitate proteins, centrifuged, diluted and injected. Tropic acid was chosen as an adequate internal standard. Separation was developed with reversed voltage by using a column cartridge pre-treated with polyacrylamide. Two electrophoretic buffers were employed: 0.150 M H3PO4 made up pH 6.20 with NaOH and 0.3 mM CaCl2 for acetoacetic, hydroxybutyric, lactic and uric acids, and 200 mM phosphate-10 mM acetate pH 4.0 for pyruvic acid, both with direct detection at 200 nm. The method was validated for linearity, accuracy and precision and the limits of quantification were calculated. The method was successfully applied to analyse these organic acids in control and diabetic animals. Acetoacetic and hydroxybutyric acids were clearly increased in diabetic rats, meanwhile no statistically significant difference has been found with the other acids.

Importance of the counterion in optimization of a borate electrolyte system for analyses of anions in samples with complex matrices performed by capillary zone electrophoresis

Borate buffers are common background electrolytes for analyses of anions in capillary zone electrophoresis. Usually, sodium borate at a given pH is used and this specification seems to be sufficient for a successful analysis. In this paper, we show that free migration of OH(-) may deteriorate the analysis of a typical anionic analysis of clinical samples due to uncontrolled migration of OH(-) throughout the systems of analyzed zones and may damage the stacking of anionic analytes of interest. We have proven that the use of ammonium borate may remedy the situation where the presence of ammonium may selectively stop the free migration of OH(-) ions, slow down their effective mobility and bring their safe behavior resulting in reproducible stacking of clinically important anions. Results of real analyses of human serum samples confirmed the proposed method and proved that substitution of sodium for ammonium in borate buffers offers reliable analyses of clinical samples having chloride as the bulk component. The experimental results given in this paper are supported also by computer simulation, which can not only support the positive results but also show the dynamics of the separation that is otherwise hidden to any detection possibilities.

Capillary electrophoresis for the determination of organic acidurias in body fluids: a review

A systematic review of the literature on capillary electrophoresis applied to short chain organic acid analysis in body fluids has been conducted with special interest on those acids related to inborn errors of metabolism. The technique is briefly described, as well as the choice of the main analytical parameters: sample pre-treatment, polarity, capillary type, background electrolyte, and detection. The applications described in the literature are listed and the main features of the technique are discussed.

Capillary electrophoresis for short-chain organic acids and inorganic anions in different samples

This review article is a comprehensive survey of capillary electrophoresis methods developed for the measurement of short-chain organic acids and inorganic anions in a wide variety of matrices, such as food and beverages, environmental, industry, and other applications, as well as clinical applications in body fluids such as urine, plasma or cerebrospinal fluid. Details of sample pretreatment and of electrophoretic conditions have been collected in tables, arranged by the type of matrix. Strategies employed for method development for the analysis of these compounds by capillary electrophoresis in real samples are discussed.

Separation methods applicable to urinary creatine and creatinine

Urinary creatinine has been analyzed for many years as an indicator of glomerular filtration rate. More recently, interest in studying the uptake of creatine as a result of creatine supplementation, a practice increasingly common among bodybuilders and athletes, has lead to a need to measure urinary creatine concentrations. Creatine levels are of the same order of magnitude as creatinine levels when subjects have recently ingested creatine, while somewhat elevated urinary creatine concentrations in non-supplementing subjects can be an indication of a degenerative disease of the muscle. Urinary creatine and creatinine can be analyzed by HPLC using a variety of columns. Detection methods include absorption, fluorescence after post-column derivatization, and mass spectrometry, and some methods have been automated. Capillary zone electrophoresis and micellar electrokinetic capillary chromatography have also been used to analyze urinary creatine and creatinine. Creatine and creatinine have also been analyzed in serum and tissue using HPLC and CE, and many of these separations could also be applicable to urinary analysis.

Determination of uric acid in human serum by capillary electrophoresis with polarity reversal and electrochemical detection

Capillary zone electrophoresis (CE) under conditions of reversed polarity is used in conjunction with electrochemical detection (EC) at carbon fiber microcylinder electrodes for the selective and sensitive determination of uric acid in human blood serum. Comigration of anions with the electroosmotic flow is accomplished with reversed polarity and the buffer additive cetyltrimethylammonium bromide (CTAB) in a 2-(N-morpholino)ethanesulfonic acid (MES) buffer system, giving rise to rapid and sensitive analyses. Optimal buffer conditions (pH 7.0), detection potential (0.80 V vs. Ag/AgCl), and electrokinetic injection are employed to allow for maximal resolution and signal intensity. Amperometric end-column detection with a carbon fiber microcylinder electrode results in lower limits of detection for uric acid of about 25 nM (ca. 140 amol injected) without the need for decoupling. Linear calibration plots using uric acid standards in water and serum are obtained over a linear range from 5.00 x 10(-4) M to 2.50 x 10(-7) M. Uric acid concentrations obtained for human sera using the CE-EC approach described here are shown to compare favorably to the accepted laboratory values.

Coupling continuous separation techniques to capillary electrophoresis

One of the weak points of capillary electrophoresis is the need to implement rigorously sample pretreatment because its great impact on the quality of the qualitative and quantitative results provided. One of the approaches to solve this problem is through the symbiosis of automatic continuous flow systems (CFSs) and capillary electrophoresis (CE). In this review a systematic approach to CFS-CE coupling is presented and discussed. The design of the corresponding interface depends on three factors, namely: (a) the characteristics of the CFS involved which can be non-chromatographic and chromatographic; (b) the type of CE equipment: laboratory-made or commercially available; and (c) the type of connection which can be in-line (on-capillary), on-line or mixed off/on-line. These are the basic criteria to qualify the hyphenation of CFS (solid-phase extraction, dialysis, gas diffusion, evaporation, direct leaching) with CE described so far and applied to determine a variety of analytes in many different types of samples. A critical discussion allows one to demonstrate that this symbiosis is an important topic in research and development, besides separation and detection, to consolidate CE as a routine analytical tool.

Determination of uremic toxins in biofluids: creatinine, creatine, uric acid and xanthines

Rapid and accurate determination of small molecule metabolic end-products is vital for clinical diagnosis and study of many metabolic disorders and medical abnormalities. Chromatographic and electrophoretic techniques are attractive for clinical analyses because of the inherent ability to analyze multiple component biofluids and determine the analytes of interest with minimal interference from other species. This manuscript reviews recent (1990-present) developments in chromatography and electrophoresis methodology for the determination of creatinine, creatine, uric acid and xanthines in biofluids.

Simultaneous determination of the urinary metabolites of toluene, xylene and styrene using high-performance capillary electrophoresis. Comparison with high-performance liquid chromatography

A simple and rapid method using high-performance capillary electrophoresis (HPCE) for the simultaneous determination of the urinary metabolites of toluene, xylene and styrene, plus creatinine and uric acid in human urine specimens and standard solutions is described. The compounds were well separated from each other on a fused-silica capillary utilizing a 20 mM sodium tetraborate buffer (pH 9.65) with 15 mM beta-cyclodextrin and UV detection at 200 and 225 nm. The total analysis time was less than 6 min per sample. The capillary zone electrophoresis (CZE) method shows a good correlation with the high-performance liquid chromatography (HPLC) method with respect to urinary hippuric acid concentrations in the urine specimens of subjects exposed to the vapors of a solvent mixture of toluene and xylene. In comparing these two techniques, HPCE was found to be superior to HPLC because the analysis time is shorter, and the separation of m-MHA and p-MHA takes a long time with HPLC.

An improved capillary electrophoresis method for measuring tissue metabolites associated with cellular energy state

An improved method for the measurement of tissue metabolites associated with cellular energetic state by capillary electrophoresis is described. This method allows 17 compounds present in a mixture of standards to be determined simultaneously within 43 min with good reproducibility. ATP, ADP, AMP, UTP, IMP, inosine, hypoxanthine, creatine, phosphocreatine, UDP-galactose, NAD and NADH were detected in samples of either rat heart tissue or rat neonatal cardiomyocytes. This method can detect compounds at concentrations of 5 microm in samples. Recoveries for ATP and phosphocreatine added to cardiomyocyte samples were 99.4 +/- 2.1% and 103.1 +/- 3.3%, respectively (mean +/- SEM, n = 3). Our method has been comprehensively validated and is capable of measuring a wider range of tissue metabolites important in assessing cellular energy status than existing methods.

Evaluation of capillary electrophoretic techniques towards systematic toxicological analysis

Two capillary electrophoresis (CE) methods were evaluated for their suitability in systematic toxicological analysis (STA). A test set of 25 barbiturates was analysed using capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). Buffers used consisted of 90 mM borate set at pH 8.4 (CZE) and 20 mM phosphate, 50 mM sodium dodecyl sulphate set at pH 7.5 (MEKC). All analyses were carried out using fused silica capillaries using an electric field strength of 52.6 kV/m. The use of a reproducible identification parameter is very important in STA as it influences the identification power (IP). To deal with the poor reproducibility of the migration time, we introduced the corrected effective mobility. Inter-day reproducibilities of the latter parameter were < 0.6% for CZE and < 0.5% for MEKC, using daily prepared buffers. The IP of the methods was expressed by calculation of the discriminating power and the mean list length. Data obtained were compared to gas chromatographic and high-performance liquid chromatographic data, and correlations between all methods were calculated. It was shown that little correlation exists between chromatographic and electrophoretic techniques. The results indicated that CE has a good identification power for the application in STA, especially when a combination of methods having a low correlation is used.

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.

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

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

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 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 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.

Capillary electrophoresis for clinical problem solving: analysis of urinary diagnostic metabolites and serum proteins

Many clinical laboratories employ gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) to detect abnormal compounds occurring in urine and serum due to disease. The methods, particularly GC-MS, often require laborious sample pre-treatment, and separation times may exceed an hour. We describe the use of capillary electrophoresis (CE) equipped a with a diode-array detector in an attempt to improve the efficiency of an analytical system routinely used for diagnosis of human metabolic disease. It was found that urine samples could be injected directly onto the CE instrument without any pre-treatment, and over 50 metabolites were separated in 15 min. Identification of abnormal metabolites was based on migration times and characteristic diode-array spectra. The method readily diagnosed adenolysuccinase deficiency, 5-oxoprolinuria, propionic acidemia and disorders have orotic acid as diagnostic metabolite (e.g. the HHH-syndrome). The results show that CE may become a useful additional tool for diagnosis of metabolic disease. In a different project CE was used to study sera from the Janus-bank. This large serum bank comprises samples collected at intervals from nearly 300,000 blood donors. As the sera are stored at -25 degrees C and not at a lower temperature, a major concern has been the stability of the specimens. GC-MS, 2D-protein electrophoresis, certain immunological assays and enzyme measurements have previously been used to evaluate the stability of the sera. We can now also show that the protein profile, as determined by CE, is remarkably stable even after 22 years of storage. The results moreover confirmed that the CE-method and traditional gel electrophoresis gave almost identical results, except for small amounts of fibrinogen which did not show up on the CE-pattern.