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Biomedical subjects

D K Lloyd

Publications and source records attributed to D K Lloyd.

34 records · Page 2Linked to original sources
PubMed1996

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.

Body Fluids↗
PubMed1996

Separation of testosterone metabolites in microsomal incubates using a new capillary electrophoresis assay.

A capillary electrophoresis method has been developed to separate the products of liver microsomal testosterone metabolism. The microsomal mixture undergoes liquid-liquid extraction and pre-concentration, and then electrophoretic analysis takes less than 25 min including capillary conditioning steps. The development of the complex background electrolyte (Tris-HCl and borate buffers, sodium dodecyl sulfate, beta-cyclodextrin and ethanol) necessary for this separation is described. A z-type capillary flow cell is used to obtain adequate detection sensitivity. The proportion in which the metabolites are produced as determined by this method allows assignment of the relative activity of cytochrome P-450 enzymes in the microsomes. The technique is useful for comparison of activity in normal and abnormal hepatic microsomes.

Animals↗
PubMed1995

Quantitation of the diastereoisomers of L-buthionine-(R,S)-sulfoximine in human plasma: a validated assay by capillary electrophoresis.

An assay for the diastereoisomers of the biochemical modifier L-buthionine-(R,S)-sulfoximine (BSO) in human plasma has been developed using capillary electrophoresis (CE). Separation of the diastereoisomers is achieved by the micellar electrokinetic chromatography (MEKC) mode of CE. Plasma is injected directly onto the separation capillary without any extraction step, and BSO is detected directly by ultraviolet absorbance measurements at 190 nm without prior derivatization. The whole assay, including capillary conditioning, takes approximately 30 min. Intra- and inter-day R.S.D. values are approximately 7% at sample concentrations around 25 micrograms ml-1, and approximately 3% at sample concentrations around 500 micrograms ml-1. The limit of detection in plasma is 3.9 micrograms ml-1 (S/N = 2). The assay has been used to quantitate the diastereoisomers of BSO in patient samples in a pharmacokinetic study.

Electrophoresis, Capillary↗
PubMed1995

Determination of the inorganic ion composition of rat airway surface fluid by capillary electrophoresis: direct sample injection to allow multiple analyses from nanoliter volumes.

The pulmonary airways are covered by a layer of airway surface fluid (ASF) which is typically < 30 microm in thickness. ASF composition is an important factor in the pathogenesis of several lung diseases including cystic fibrosis. Because of the very small volume of ASF, it is difficult to determine ASF composition, Particularly for inorganic ions, since sampling by lavage is not suitable. With nanoliter injected volumes, capillary electrophoresis (CE) is ideally suited to ASF analysis. We have developed a novel technique using separate sampling and injection capillaries whereby submicroliter volumes of ASF (typically approximately 100 nL) can be collected from airways and then analyzed by CE. Cations (Na+, K+, Ca2+, Mg2+) and anions (including Cl-) are quantitated (RSD < 10%) using indirect UV detection. In healthy rat lungs, ASF was found to be hypotonic, consistent with observations made in human airways. This technique has been developed using rats, which have not previously been studied because their small size prohibits the use of other sampling techniques.

Animals↗
PubMed1995

Sodium dodecyl sulfate solution is an effective between-run rinse for capillary electrophoresis of samples in biological matrices.

It is common practice in capillary electrophoresis to perform some sort of capillary washing step(s) between separations. In many analyses little consideration is given to optimization of the wash, and typically a rather standard washing procedure is used involving a few minutes wash with 0.1 M NaOH followed by a few minutes reconditioning with the run buffer. As an alternative to this procedure, we have investigated the use of wash solutions containing sodium dodecyl sulfate (SDS). This type of wash has been used in the analyses of both small molecules and proteins, with encouraging results. After the SDS wash, the electroosmotic flow has been shown to be restored to values close to normal in a capillary which had previously been coated with plasma proteins. Separation efficiency for a test compound (dextromethorphan) is improved if an SDS rather than a HCl-NaOH wash is used after injection of plasma. In a direct-injection analysis of plasma proteins using a pH 10 borate buffer, an SDS-based washing procedure (total time, 1 min) gave better migration-time reproducibility than an NaOH-based wash, which took 5 min in total.

Blood Proteins↗
PubMed1995

Effect of pH and sodium dodecyl sulfate concentration on the analytical window in the direct-injection analysis of plasma samples by capillary electrophoresis.

Plasma samples can be analyzed with direct injection onto a capillary electrophoresis system if interactions between the plasma proteins and capillary walls are minimized. This can be achieved using micellar electrokinetic capillary chromatography with a surfactant such as sodium dodecyl sulfate. The surfactant complexes with the proteins, giving them a net negative charge, and thus causes them to be repelled from the negatively-charged fused-silica capillary walls. Migrating as anions, the complexed proteins appear late in the electropherogram. In such analyses, it is important to manipulate the mobility of the analyte(s) of interest such that they migrate in the useful analytical time window before the plasma proteins. In this article, a study of the effect of buffer pH and surfactant concentration on the width of the migration time window is reported. It is shown that at pH 6 the migration time window is wide, but reduced electroosmosis can result in inordinately long run times; pH 7 gives an acceptable analytical window with acceptable run times over a wide range of sodium dodecyl sulfate (SDS) concentrations; pH 8 and higher are most useful when higher concentrations of surfactant (> 50 mM SDS) are employed.

Acetaminophen↗
PubMed1993

The safety of sumatriptan in asthmatic migraineurs.

A recent report has questioned the safety of sumatriptan in asthmatic migraineurs. To investigate this, we have reviewed the sumatriptan clinical trial safety database of over 75 completed trials. Within the clinical trial database, 375 asthmatic patients were identified who treated 1214 migraine attacks with sumatriptan. The incidence and nature of adverse events in the asthmatic patient subgroup who received sumatriptan was similar to that in the complete clinical trial population. Six reports of asthma were recorded as adverse events, but only one case was classified by the investigator as related to treatment. There is no clinical or pharmacological evidence to suggest that the safety profile of sumatriptan is altered in asthmatic patients compared to other migraine sufferers.

Asthma↗
PubMed1992

Determination of N-acetylator phenotype using caffeine as a probe compound: a comparison of high-performance liquid chromatography and capillary electrophoresis methods.

A test for determining N-acetylator metabolic phenotype has been developed using caffeine as a probe drug. A spot sample of urine is taken, and the unextracted urine is then analysed by micellar electrokinetic capillary chromatography. Phenotype is determined from the peak-area ratio of urinary 5-acetylamino-6-formylamino-3-methyluracil to 1-methylxanthine. Phenotype assignments using this method were compared with those made using a standard high-performance liquid chromatography assay, with good agreement between the two methods. The advantage of the capillary electrophoresis analysis is that no sample extraction is necessary, resulting in a total analysis time of around 20 min, and removing a potential source of error.

Acetylation↗
PubMed1992

Migraine.

Explore the source record for details and available documents.

Humans↗
PubMed1991

Determination of cytosine-beta-D-arabinoside in plasma using capillary electrophoresis.

An assay for the antileukaemic agent cytosine-beta-D-arabinoside (ara-C) has been developed using capillary zone electrophoresis. Solid-phase extraction and on-capillary peak concentration are used to improve the detection limit. The electrophoretic separation time is less than 5 min. The limit of detection for ara-C in plasma is 0.5 microM (signal-to-noise ratio = 3). The assay has been validated for the determination of ara-C in human plasma over the concentration range 1-10 microM. The calibration curve was linear with a correlation coefficient r2 = 0.996. At an ara-C concentration of 8 microM the intra-day coefficient of variation was 9.1% and the inter-day coefficient of variation was 12.3%. At an ara-C concentration of 2 microM the coefficients of variation were 15.2 and 12.0%, respectively.

Cytarabine↗
PubMed1990

Determination of enantiomeric purity of ephedrine and pseudoephedrine by high-performance liquid chromatography with dual optical rotation/UV absorbance detection.

A reversed-phase high-performance liquid chromatography (HPLC) method with dual optical rotation/UV absorbance detection has been developed for the determination of enantiomeric purity of ephedrine hydrochloride and pseudoephedrine hydrochloride using an achiral column. The method gave a correlation coefficient of 0.9997 for the plot of log(optical rotation response) versus log (concentration) over the range of 0.06-10 mg ml(-1) of (+)-ephedrine hydrochloride (20 microliters injection). The limit of detection was 1.0 micrograms. Enantiomeric purity is shown to be most readily determined by measuring optical rotation, alpha, and absorbance, A, responses for standard and unknown samples, and using the equation (alpha/A)u/(alpha/A)s = (2xu - 1)/(2xs - 1), where x is the mole fraction of one of the enantiomers and subscripts s and u refer to standard and unknown, respectively. In blind trials using unknown mixtures of (+)- and (+/-)-ephedrine hydrochloride and a (+)-ephedrine hydrochloride standard, enantiomeric purities were determined to +/- 0.4% (95% confidence level) with five or six replicate 50 micrograms injections. The method has also been applied to the determination of the enantiomer mole fraction of (+)-pseudoephedrine hydrochloride in a cough linctus, giving xu = 0.99 +/- 0.01 with seven replicate injections of 20-fold diluted linctus samples containing 7.5 micrograms of the chiral compound being assayed. Unlike conventional polarimetry, the method does not require chemically-pure samples and can be orders of magnitude more economical in material.

Antitussive Agents↗
PubMed1989

Polarimetric detection in high-performance liquid chromatography.

Chiroptical detection for HPLC is particularly useful as a selective detection method for chiral molecules, and in enantiomeric purity determination with partial chiral separation or without chiral separation. The recent development of laser-based polarimeters with microdegree sensitivity has increased the applicability of optical rotation detection in HPLC. The detection limit of these instruments is submicrogram on-column for many chiral compounds in analytical HPLC. A variety of applications of the selective detection of optically active molecules are reviewed. The use of polarimetric detection with partial chiral separation is considered, both as an aid to method development and for enantiomeric purity determination. Finally applications to enantiomeric purity determination without chiral separation are reviewed, with the dual use of nonchirally selective and chiroptical detectors to determine the total amount and optical purity of the analyte. Determinations of chiral purity for samples of high enantiomeric excess are described, which with laser-based instrumentation may give accuracies of better than +/- 1% with sample loadings of 50 micrograms on an achiral column. Applications to the study of enantioselective reactions are also considered, with determination of enantiomeric excess in near-racemates to better than +/- 0.1%.

Chromatography, High Pressure Liquid↗