Determination of opiates in urine by capillary electrophoresis

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.

Head-column field-amplified sample stacking in binary system capillary electrophoresis. 2. Optimization with a preinjection plug and application to micellar electrokinetic chromatography

In capillary electrophoresis, head-column field-amplified sample stacking (FASS) provides the largest sensitivity enhancement of all electrokinetic concentration techniques (Zhang, C.-X.; Thormann, W. Anal. Chem. 1996, 68, 2523). Application of head-column FASS to the analysis of closely related opioids by capillary zone electrophoresis in binary systems with ethylene glycol is described. It is shown that sample condensation is further increased about 2-fold by introduction of a preinjection plug, i.e., introduction of a short solution plug of high conductivity, high pH, and high viscosity at the capillary tip prior to injection. The preinjection plug acts as a temporary trap for solutes. Its effective length is shown to be limited to a few millimeters. The highest sample stacking efficiency in head-column FASS is obtained via optimization of the electric field strength and the effective electrophoretic mobility of the solutes within the sample and the adjacent zones and is thus strongly dependent on the compositions of both the sample matrix and the preinjection plug. Binary sample solutions of low conductivity and low viscosity containing small amounts of a weak acid are demonstrated to be most effective for the stacking of positively charged opioids. The procedure developed for capillary zone electrophoresis of opioids in binary systems with ethylene glycol and UV absorbance detection is documented to provide a 3 orders of magnitude sensitivity enhancement, exhaustive sample injection from an external reservoir of up to 20 microL (i.e., from a volume that is more than 20-fold the volume of the capillary employed), and a lowest detectable concentration of 0.1 ng/mL (S/N = 3). Using internal calibration, typical intraday and interday imprecisions of solute concentrations between 3 and 10 ng/mL and between 0.5 and 1.5 ng/mL are < or = 5% and < or = 15%, respectively. The stacking approach has been successfully applied to the analysis of dihydrocodeine in extracts of 20 microL of human plasma and is shown to permit the precise (imprecision < or = 10%) determination of dihydrocodeine plasma levels of pharmacological interest (3-300 ng/mL or 10-1000 nM). Furthermore, using a modified protocol for micellar electrokinetic chromatography, head-column FASS is shown to provide a 400-fold sensitivity enhancement for a number of opioids. The stacking procedure is based on insertion of a surfactant-free preinjection plug and temporary application of reversed voltage after electroinjection.

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.