Biomedical subjects

Edmund T Bergström

Publications and source records attributed to Edmund T Bergström.

5 recordsLinked to original sources

PubMed2006

1,4-Benzoquinone-based electrophoretic assay for glucose oxidase.

The communication demonstrates feasibility of an enzyme microassay for glucose oxidase with 1,4-benzoquinone as an acceptor of electrons. The protocol uses the plug-plug mode of electrophoretically mediated microanalysis, with nanolitre injected volumes of enzyme and reactant solutions. The reactant and product, 1,4-benzoquinone and hydroquinone, are separated during the assay by differential binding to sulfated-beta-cyclodextrin used as additive to the phosphate buffer (pH 7) and monitored at selected wavelengths in their UV spectra. The assay covers glucose oxidase concentration from 0.01 to 0.1mgml(-1). Due to the strong UV absorbance of the both reactant and product, there is no need for use of a second enzyme (peroxidase) in the present assay.

Benzoquinones↗

PubMed2006

On-line low-volume transesterification-based assay for immobilized lipases.

A method has been developed for fast evaluation of transesterification activity of immobilized lipases using microlitre and submicrolitre volumes of substrate solutions. The model reaction (acylation of isopropanol with vinyl acetate) is catalyzed by microbial lipases immobilized on ceramic particles, diatoms or acrylic resin, packed into a Teflon tube connected to fused-silica capillary tubing. The substrate solution is pumped through the microreactor and the product of transesterification, acetaldehyde, quantified on capillary by UV absorbance at 280 nm. Using this system in the continuous-flow mode, comparisons were made of transesterification catalysed by PS-C II lipase in two different solvent mixtures. Acetonitrile was found to be a compatible solvent that can be used as a solubilizer without suppressing enzymatic activity. The method has been used to compare conversions at a fixed flow rate using a single pass of substrate through packed beds containing approximately 0.2 mg of supported enzyme. Spatial distributions of the product have been visualized using a complementary metal oxide semiconductor (CMOS) imaging detector in conjunction with the microreactor system operated in the stopped-flow mode.

Acetonitriles↗

PubMed2006

Real-time image acquisition for absorbance detection and quantification in thin-layer chromatography.

This paper presents the first quantitative study of real-time acquisition of images of spots on thin-layer chromatographic plates during development. Procedures are described for imaging using a CCD camera and for image processing, incorporating corrections for fixed pattern effects and compensation for the moving solvent front, to measure the absorbance of the analyte. Imaging of Sudan II was carried out in transmission mode, and peak areas were found to be time-independent. Quantification of the relationship between peak area and sample loading was established over the range 1-50 ng. After averaging 55 images obtained during a single chromatographic run, which attenuates noise contributions from local nonuniformities in the sorbent layer, precision and detection limits were found to be comparable with values obtained in previous work using offline measurements.

Azo Compounds↗

PubMed2005

Quantitative measurements on wetted thin layer chromatography plates using a charge coupled device camera.

This paper presents the first study of imaging of spots on thin-layer chromatographic plates whilst still wet with solvent. Imaging and quantification of Sudan II after development with dichloromethane was carried out in both reflectance and transmission modes, using a charge coupled device (CCD) camera. The relationship between peak area and sample loading was established at low sample loading, and found to be linear over an order of magnitude for both wet and dry modes with r2-values > 0.99. All data processing was carried out using the Beer-Lambert equation. Curvature at high loadings in the plots of integrated absorbance as a function of sample loading was accounted for using an empirical expression designed for use with the Kubelka-Munk treatment and apparent absorbance of the stationary phase due to scattering. Results are consistent with an effective pathlength significantly longer than the thickness of the sorbent layer. The limit of detection on a dry plate (0.5 ng) was found to be lower than on a wetted plate (2 ng). Precision was found to be 1-4% RSD intra-plate and 8-14% RSD inter-plate. Results are compared with quantification of the same analyte on dried plates.

Azo Compounds↗

PubMed2002

Electromigration dispersion in capillary zone electrophoresis. Experimental validation of use of the Haarhoff-Van der Linde function.

This paper provides experimental validation of the use of the Haarhoff-Van der Linde (HVL) peak fitting function to fit experimental capillary zone electrophoresis (CZE) electropherograms. The test mixtures were composed of paraquat over a five order of magnitude concentration range (1.2 microM to 120 mM) and 4-aminopyridine at constant concentration (0.53 mM) as internal standard. Peak descriptors and electrophoresis parameters were extracted reliably by a Gaussian function from 4 to 40 microM; by the HVL function from 120 microM to 4 mM; and by a triangular function from 4 to 120 mM. The HVL function can be used where there is significant peak asymmetry due to electromigration distortion (EMD) and the Gaussian contribution toward the peak variance is greater than 25%. The peak centre (a1) and the Gaussian variance (a2) of the paraquat peak are shown to be independent of concentration. Diffusion coefficients obtained from a2 for both analytes were found to be in good agreement with their theoretical values. For all peaks where the distortion coefficient (a3) can be extracted, this parameter is shown to be directly proportional to the sample loading, as predicted by EMD theory. For the 4-aminopyridinium ion, mobilities calculated from a3 and measured independently are in excellent agreement. These results show that the HVL function accurately describes the two major processes, diffusion and EMD. contributing to the variance during a CZE separation.

Electrophoresis, Capillary↗