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Biomedical subjects

A F Fell

Publications and source records attributed to A F Fell.

51 records · Page 3Linked to original sources
PubMed1984

Analysis and characterisation of aromatic amino acids, metabolites and peptides by rapid-scanning photodiode array detection in high-performance liquid chromatography.

The role of rapid-scanning UV detectors based on the linear photodiode array has been examined in studies on the chromatography of aromatic amino acids, some metabolites and peptides. Multichannel detectors can generate characteristic qualitative information presented as individual spectra, as three-dimensional spectrochromatograms or as contour maps in the (lambda, t) plane. The use of such contour plots for mapping amino acids and their metabolites, and for peptide mapping Tyr-Gly, Gly-Tyr, Phe-Gly, Tyr-Tyr and Phe-Val, is examined. The application of computer-aided methods for validating peak homogeneity by spectral suppression, second derivative in the time domain and by other methods is discussed with respect to Tyr and its metabolite dopamine, which are not resolved by the system described, and which have closely similar spectral characteristics. The use of colour graphics with the IBM Personal Computer is demonstrated for simplifying the presentation of contour maps of amino acids, metabolites and dipeptides.

Amino Acid Sequence↗
PubMed1983

Applications of rapid-scanning multichannel detectors in chromatography. Plenary lecture.

A review of progress in the field of multichannel detection in column and thin-layer chromatography is presented, together with some novel applications of a computer-based, linear photodiode array UV--visible spectrophotometer for detection in high-performance liquid chromatography (HPLC). Computer-aided methods for simultaneous monitoring of the elution profile at three wavelengths with automatic peak detection and capture of UV spectra are described. The continuous calculation of absorbance ratios during elution is discussed as an index of peak homogeneity. A novel technique for the enhancement of qualitative identification in HPLC, based on transformation of captured spectra to the second derivative or to the decadic logarithm, is proposed. These developments are exemplified by a model system of diacetylmorphine and its principal metabolites and degradation products, morphine and 6-acetylmorphine. The potential utility of three-dimensional projections of (A, lambda, t) data is discussed in the context of pharmaceutical, bioanalytical and forensic applications.

Chromatography, High Pressure Liquid↗
PubMed1983

Editorial.

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Editorial↗
PubMed1983

Novel applications of multichannel spectroscopy in pharmaceutical analysis.

Multichannel detectors based on the linear photodiode array, the silicon vidicon tube and charge coupled (or injection) devices are reviewed with reference to their applications in analytical spectroscopy and high-performance liquid chromatography (HPLC). The use of computer-aided techniques, including second derivative spectroscopy and spectral deconvolution methods, for the multichannel spectroscopic analysis of pharmaceuticals is discussed, and applications are reviewed in clinical chemistry, enzyme analysis and studies on aromatic amino acids in proteins. In HPLC, the principles and applications of digital algorithms for validation of peak homogeneity are considered, with reference to spectral suppression, spectral deconvolution, absorbance ratio and the second derivative of the elution profile. The isometric projections of (A, lambda, t) data, and their cartographically equivalent contour plots, are discussed and the impact of multicolour graphics is assessed. The implications of two-dimensional multichannel detectors for detection of luminescence radiation are considered in the context of analytical spectroscopy, and detection in both HPLC and thin-layer chromatography. The potential contribution of charge coupled and charge injection devices as the next generation of multichannel detectors is considered.

Journal Article↗
PubMed1981

A rapid method for the emergency analysis of paraquat in plasma using a second derivative spectroscopy.

A rapid method for the analysis of paraquat in plasma of poisoned patients is described. The dithionite colour reaction is used to detect paraquat, and matrix interference is eliminated by the use of a chemical deproteinization technique followed by second derivative spectroscopy of the reaction mixture. The method was compared with an established procedure using ion-pair extraction followed by dithionite reduction. Sensitivity and precision were comparable and the correlation in patients' plasma was good. The proposed direct method is rapid and suitable for emergency use in the management of patients poisoned with paraquat.

Blood Proteins↗
PubMed1981

Analysis for paraquat by second- and fourth-derivative spectroscopy.

We describe simple, precise methods, based on second and fourth-derivative spectroscopy, of analysis for paraquat in serum, plasma, or dialysis fluid. Plasma paraquat, after ion-pair extraction and dithionite reduction, yields a sharp, stable absorption peak at 396 nm. Derivative spectroscopy confers enhanced sensitivity (detection limit, 5 microgram/L) and improved rejection of spectroscopic interference by diquat, hemolysis, bilirubin, or lipemia. Derivative peak amplitudes are linearly related to paraquat dichloride concentration from 10 to 1000 microgram/L in plasma, and the methods are precise (CV 2.7-5.2% for 50 microgram/L concentration) and accurate. Results of derivative assays for 18 cases of paraquat poisoning correlate well with those by radioimmunoassay (r = 0.999). Derivative spectroscopy enables monitoring of paraquat concentrations in the plasma of poisoned patients during treatment by hemoperfusion or hemodialysis. A rapid assay developed for dialysis fluid (detection limit, 2 microgram/L) permits the efficacy of hemodialysis to be routinely assessed.

Diquat↗
PubMedDate not supplied

Assessment of chromatographic peak purity of drugs by multivariate analysis of diode-array and mass spectrometric data.

Numerous multivariate chemometric approaches have been developed for LC-UV data acquired using a diode-array detector (DAD), but these methods have not been widely exploited for LC-MS data. Principal component analysis (PCA) and subsequent axis rotation within the reduced factor space are assessed for LC-DAD and LC-MS data as approaches for estimating the number of components (i.e. the rank of the data) under a single chromatographic peak for compounds whose UV-spectra are very similar. Multivariate techniques for LC-DAD data are shown to suffer from inherent limitations of sensitivity for the minor components. The novel technique in LC-MS of plotting the rotated PCA data in two-dimensional factor space generates characteristic ion clusters, giving a visual criterion of peak purity. Single ion chromatograms produced subsequently confirm the profile of each coeluting component and give evidence of the degree of peak overlap. The application of this new chemometric technique to the detection of low levels of coeluting impurities by LC-MS is discussed as a novel approach for the validation of LC separations in pharmaceutical research and development.

Chromatography, Liquid↗
PubMedDate not supplied

Design of chiral LC separations for calcium antagonists on alpha 1-acid glycoprotein and ovomucoid columns.

Three chiral calcium antagonist drugs, gallopamil and two dihydropyridine derivatives, have been successfully separated within short retention times using both the alpha 1-acid glycoprotein chiral stationary phase (Chiral-AGP) and the ovomucoid column (Ultron ES-OVM). Aqueous buffer at defined pH is modified by the addition of an organic component, in order to modulate the retention properties of each system. Optimization of pH and organic modifier is carried out using the modified simplex method, with Kaiser's peak separation function as a criterion. The influence of pH and percentage of organic modifier on retention, selectivity, resolution and column performance are discussed for the two dihydropyridines analysed on Chiral-AGP and Ultron ES-OVM stationary phases. A new method is proposed as a new chiral system suitability test for these protein-based phases, utilizing a racemic mixture of closely eluting verapamil enantiomers as a probe.

Calcium Channel Blockers↗