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Biomedical subjects

A F Fell

Publications and source records attributed to A F Fell.

At least 37 records · Page 2Linked to original sources
PubMed1990

Post-column continuous-flow analysis combined with reversed-phase liquid chromatography and computer-aided detection for the characterisation of peptides.

Peptide mapping is a key technique for structural identification of new proteins or the products of recombinant gene technology. The recognition of oligopeptides, separated by reversed-phase liquid chromatography, is limited by the conventional reliance on the correlation of retention times with standards, supported by dual-wavelength chromatograms. It has been reported that the recognition of phenolic compounds can be achieved by a novel technique, based on computer-aided photodiode-array detection of the pH-shifted solutes after post-column continuous-flow analysis. This work describes how the generation of the pH-shifted difference spectra for dipeptides, containing a tyrosyl residue, may be used to enhance peak recognition, when used in conjunction with absorbance ratios.

Absorptiometry, Photon↗
PubMed1990

High-performance liquid chromatographic resolution of oxamniquine enantiomers: application to in vitro metabolism studies.

A method is described for the HPLC analysis of oxamniquine enantiomers in liver fraction incubates, using a second-generation alpha 1-acid glycoprotein-based column (Chiral-AGP). Oxamniquine is extracted from the incubation media by liquid-liquid extraction, using diethyl ether. The dried residue is redissolved in eluent, filtered, then injected directly onto the analytical column. The extraction method affords recoveries of oxamniquine of approximately 93%, at concentrations up to 525 micrograms/ml, with an average relative standard deviation of 5.9%. The limit of detection of the method (to give an SNR = 2 at 246 nm) is 0.3 ng on-column for the first eluting, laevorotatory enantiomer and 2.3 ng for the dextrorotatory isomer. The method allowed study of the depletion of oxamniquine enantiomers in liver postmicrosomal incubates. In the rat, a turnover of 21.9% was observed, with no apparent enantioselectivity. Similar observations were made for a mouse liver subcellular fraction incubation. The absence of enantioselectivity in this biotransformation may be attributable to the low substrate specificity of the oxidase or dehydrogenase enzymes involved.

Animals↗
PubMed1990

Chromatographic and spectroscopic studies on the constituents in male and female flowers of Hagenia abyssinica.

The phenolic constituents of male and female flowers of Hagenia abyssinica were examined using chromatographic and spectroscopic techniques. Chromatographic analysis of kosins (phloroglucinols) was carried out using TLC, reversed-phase LC and glass-capillary GLC. Purification of the crude kosins was effected by silica gel column chromatography and purification of phenolic acids using ion-exchange resins and preparative TLC on silica gel. The kosins were characterized by TLC, LC, UV, IR, MS and H1 NMR spectroscopy while the phenolic acids were characterized by UV-spectroscopy, TLC and LC. The phenolic acids found were protocatechuic acid, p-hydroxybenzoic acid and vanillic acid. The content of the kosins and phenolic acids was established quantitatively for both male and female flowers.

Africa, Eastern↗
PubMed1989

Reversed-phase high-performance liquid chromatographic method for the quantification of 5-hydroxymethylfurfural as the major degradation product of glucose in infusion fluids.

Analysis of 5-hydroxymethylfurfural (5-HMF) is an important indicator of degradation in glucose infusion fluids. Current pharmacopoeial methods for analysis are insensitive and non-specific. A method is described here, incorporating an internal standard, to give a sensitive, accurate and precise method, suitable for use in the quality control of glucose infusion fluids, and with possible applications for the quantitative determination of 5-HMF in food and drink, bacterial cultures and hydrothermolysed wood.

Chromatography, High Pressure Liquid↗
PubMed1989

Development and optimisation of a high-performance liquid chromatographic assay for tioconazole and its potential impurities. I. Selection of separation conditions.

Statistical mixture design techniques have been utilized to develop an isocratic high-performance liquid chromatographic separation of 1-(2- [(2-chloro-3-thienyl)-methoxy]-2-(2,4-dichlorophenyl)ethyl)- 1H-imidazole (tioconazole) and its potential impurities. By using suitable quality criteria such as reduced plate height, peak asymmetry and selectivity for the interrogation of chromatograms the variables producing best column efficiency and greatest selectivity have been identified. The optimum separation for these variables has been located by the sequential simplex approach and confirmed by response surface mapping.

Chemical Phenomena↗
PubMed1989

In vitro metabolism studies on oxamniquine and related compounds by chiral liquid chromatography.

A previously developed method based on alpha 1-acid glycoprotein for the resolution of the enantiomers of the Pfizer antischistosomal drug oxamniquine was used to examine possible enantioselectivity in the in vitro microsomal hydroxylation of a metabolic precursor, UK-3883, but was found to be limited by the poor operational stability of the analytical column ("EnantioPac") employed. As an alternative approach, a "Pirkle" covalently-bonded dinitrobenzoyl leucine column was used, with simple precolumn solute derivatization to the carbamate to improve chromatographic performance. The method allowed preliminary examination of the stereochemistry of the in vitro biotransformation, hydroxylation of UK-3883 to oxaminquine, which yielded evidence for substrate enantioselectivity in favour of the dextrorotatory enantiomer of UK-3883.

Animals↗
PubMed1989

Development and optimisation of a high-performance liquid chromatographic assay for tioconazole and its potential impurities. Part II. Selection of detection conditions for potential impurities.

An optimised high-performance liquid chromatographic separation developed for the assay of tioconazole and its potential impurities has been applied to real-world samples where tioconazole is in excess. As severe peak tailing interferes with the assay of two of the impurity peaks, changes in detection wavelength have been examined as a means to discriminate between this interference. The resulting enhancement of resolution has been exploited in the optimisation of analysis time.

Chromatography, High Pressure Liquid↗
PubMed1989

HPLC studies on the degradation profiles of glucose 5% solutions subjected to heat sterilization in a microprocessor-controlled autoclave.

A practically useful relationship between degradation and F0 at various temperatures is given. This may be of value for identifying the most suitable sterilization conditions for a number of glucose products and other pharmaceuticals. It was found that autoclaving at a high temperature to a low final F0 value gave the maximum product integrity.

Chromatography, High Pressure Liquid↗
PubMed1989

Analysis of supplemented vitamin K1(20) in serum microsamples by solid-phase extraction and narrow-bone HPLC with multichannel ultraviolet detection.

A sensitive method for the determination of vitamin K1(20) in serum microsamples (50 microL) has been developed, utilizing solid-phase extraction with C8 Bond-Elut columns and reversed-phase narrow-bore high-performance liquid chromatography [2.1 mm (i.d.), column] with a nonaqueous eluent. Recovery from serum (49 ng/mL) was 76% (n = 2). Peak homogeneity was assessed by photodiode array detection with absorbance ratio, spectral normalization, and transformation to the first- and second-derivative chromatograms. Calibration data at 248 nm over two ranges (20-200 ng/mL, 200-4000 ng/mL) varied linearly with concentration and were suitable for studies of vitamin K1 supplementation. By comparison with conventional columns, sensitivity was increased twofold.

Chromatography, High Pressure Liquid↗
PubMed1988

Computer-aided optimisation of drug enantiomer separation in chiral high-performance liquid chromatography.

The advent of several new column materials for the resolution of chiral compounds in high-performance liquid chromatography has opened up new possibilities for the analysis of drug enantiomers both in the dosage form and in bioanalytical studies. The utility of simplex optimisation, modified simplex and response surface mapping are considered with reference to the antischistosomal drug, oxamniquine, separated on an alpha 1-acid glycoprotein column. The resolution of the enantiomers of three closely related benzodiazepines, temazepam, oxazepam and lorazepam, is attempted on three new column systems: cellulose triacetate, beta-cyclodextrin and the reversed-phase column porous graphitic carbon with beta-cyclodextrin as a mobile phase additive.

Chromatography, High Pressure Liquid↗
PubMed1988

Design and application of an expert system for mobile phase optimisation in reversed-phase liquid chromatography.

The selection of the optimum composition for the mobile phase in reversed-phase high-performance liquid chromatography (HPLC) is a complex task; conventional approaches require the expenditure of significant amounts of time by the analyst, particularly for complex mixtures of solutes of biological origin. Some of the existing strategies for the automated optimisation of mobile phase composition (e.g. Simplex), may fail if the elution order of the components changes; or they may require that standards be chromatographed in order to establish the retention behaviour of each component in a mixture (e.g. resolution mapping). These problems may be overcome if the retention behaviour of each individual solute can be established from the chromatogram of the mixture. In this regard, components can be tracked by exploiting the spectral information generated by a rapid scanning photodiode array detector. Unfortunately this information is often insufficiently detailed to allow an unambiguous model of retention behaviour to be constructed. The system developed by the Authors uses these spectral data as a basis for constructing one or more hypothetical retention models, each of which is refined or rejected as further information is obtained during the progress of the experiment. To improve the reliability of the retention models proposed by the system, the spectral data are utilised in a number of tests designed to assess the purity of each chromatographic peak. The information so generated may be used in conjunction with any previously acquired spectral data both to select an appropriate method for extracting spectra for each component from the matrix of (A, lambda, t) data and to establish reliability parameters for the resultant spectra. The development and philosophy of the expert system developed for eluent optimisation in reversed-phase HPLC is discussed.

Journal Article↗
PubMed1988

Digital techniques for luminescence detection in liquid chromatography with an intensified linear photodiode array.

The use of a rapid-scanning fluorescence detector in liquid chromatography is examined in the context of its potential contribution in pharmaceutical and biomedical analysis. The data generated by an intensified linear photodiode array detector is presented as an isometric plot of (I(em),lambda(em),t) at a defined excitation wavelength. Techniques examined for peak homogeneity assessment include: emission spectral normalisation at points through the chromatographic peak profile, second order differentiation (d(2)I/dt(2)) and the fluorescence emission ratio chromatogram, generated by calculating the ratio of emission intensifies at two defined emission wavelengths, at all points in the time domain elution profile. These techniques are illustrated with reference to some polynuclear aromatic hydrocarbons and to the beta-blocker drug atenolol and its related impurities. Future developments of this new detector technology in LC are also considered.

Journal Article↗
PubMed1987

An HPLC assay procedure of sensitivity and stability for measurement of acetylcholine and choline in neuronal tissue.

A method is presented for the sensitive and specific determination of acetylcholine and choline in neuronal tissue. The method is based on the separation of acetylcholine and choline by reversed-phase HPLC, passing the eluent into a post-column reactor containing choline oxidase and acetylcholinesterase covalently bound to vinyl sulphone bonded onto a hydroxyethyl methacrylate support, and electrochemical detection of the hydrogen peroxide formed. The limit of detection of the procedure is 1 pmol for acetylcholine and 500 fmol for choline. The excellent baseline stability of the method ensures the rapid and reliable processing of a large number of samples.

Acetylcholine↗
PubMed1987

Caffeine as a potential indicator for acetylator status.

The identification of patients as 'fast acetylators' or 'slow acetylators' is used in clinical practice to help recognize those at risk from toxicity and in guiding the dosage of N-acetylated drugs. Caffeine has been proposed as a marker for drug acetylation on the basis of a ratio of urinary metabolites (5-acetylamino-6-formylamino-3-methyl uracil and 1-methylxanthine, AFMU:MX) determined by high-performance liquid chromatography. The caffeine test was studied in 26 subjects by reference to the use of sulphamidine as the test substance. The distribution of urinary AFMU:MX ratios allowed assignment of subjects to 'slow' and 'fast' acetylator status (AFMU:MX less than 2.1 and greater than 2.3 respectively). The results showed accordance with those from the sulphadimidine test with the exception of one subject. The possible interference of concurrent administration of sulphadimidine (as an example of a drug known to undergo metabolism by N-acetylation) was also studied in 11 of the subjects. The interference was found to be small (apparent mean bias 11%) but of possible clinical significance.

Acetylation↗
PubMed1984

Computer-aided strategies for archive retrieval and sensitivity enhancement in the identification of drugs by photodiode array detection in high-performance liquid chromatography.

An archive retrieval algorithm for high-performance liquid chromatography with UV detection (HPLC-UV) has been developed for the first time for the rapid identification of spectra acquired by rapid-scanning photodiode array detection in HPLC. The algorithm is based on a database of spectra (normalised with respect to area), inverse files of key spectral features, a selective search window, with parabolic weighting factors and least-squares comparison of test and retrieved spectra. The performance of the library search system is demonstrated with respect to a small library of solutes, including: cortisone acetate, ethynyl estradiol, ethisterone, progesterone; caffeine, theobromine, theophylline and 8-chlorotheophylline; morphine and diamorphine; and cycloserine. Since photodiode array detection operates in the domains of both wavelength and time, to generate a matrix of (A, lambda, t) data, the optimum conditions for sensitivity enhancement by ensemble averaging in these domains have been examined. At a given observation wavelength, increase in the detector bandwidth (or "diode bunching") yields a value of delta lambda which gives optimum sensitivity; this value is systematically related to the spectral bandwidth of the analyte. Sensitivity can also be optimised by varying the integration period in the time domain. Sensitivity can be further increased by combination of these instrumental optima, for which there is evidence of dependence on the particular instrument design. Response was found to be linear for detector bandwidths up to twice the optimum value. The comparative sensitivity of some commercially-available photodiode array detectors has been assessed relative to that of conventional detectors under strictly controlled conditions.

Chromatography, High Pressure Liquid↗