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Biomedical subjects

J A Howell

Publications and source records attributed to J A Howell.

13 recordsLinked to original sources
PubMed1994

Operational properties of an inverted matrix cellulose CM ion-exchanger.

Productive CM is a recently available carboxymethyl ion-exchanger based on cellulose supplied by BPS Separation. It is supplied in an 'inverted matrix' form as a coherent structure with large voids and about 90% free volume. This paper reports mainly on the physical properties and robustness under normal use conditions using lysozyme as a model protein. The structure is shown by electron microscopy to be formed of fibrous or sheet material around macropores of around 100 microns in diameter. The material around the macropores is itself porous down to the smallest pores visible at perhaps 50 nm. The capacity under static and dynamic conditions was measured and found in both cases to be only slightly dependent on applied flow velocities up to 8 m h-1. The high porosity allowed cider fermentation broth and diluted egg white to be applied directly to a column without blockage and at a moderate pressure drop yet with a high superficial velocity. Compression of the bed at high flow rates did not occur at free space velocities up to 17 m h-1 with water and slightly lower with other fluids. The adsorption isotherm was determined and found to follow a Langmuir form. It proved to be totally stable to immersion in 1 M NaOH and 1 M NaCl without any measurable volume changes. Many of the properties were compared with those of other ion-exchange resins and found to be equivalent in capacity but superior in terms of stability, sustainable flow rates and dynamic capacity. It is concluded that the stability, performance under high flow rates and good capacity make it eminently suitable for use in large scale applications.

Adsorption↗
PubMed1991

Resolution and productivity of conalbumin and lysozyme from fresh egg-white loaded at very high flow rate on a 250-mm length CM-HVFM column.

A 250 x 10 mm I.D. column of CM-HVFM, a novel carboxymethyl ion-exchange matrix, has been used as a preparative chromatographic column to separate fresh egg-white protein. When loading a diluted egg-white solution at pH 4.8 ovalbumin was not adsorbed and lysozyme was preferentially adsorbed compared to the conalbumin. As the column loading was increased from 24 to 450 kg m-3 column volume at the superficial velocity of 6.12 m h-1, the lysozyme continued to be absorbed eventually displacing conalbumin. A maximum lysozyme productivity at 16.7 kg m-3 h-1 was achieved at the highest loading. For conalbumin a maximum productivity of 8.8 kg m-3 h-1 occurred at the lower loading of 100 kg m-3. The purities of lysozyme and conalbumin were comparable at a column loading of 450 kg m-3 h-1. The performance of the column was not degraded, neither was the column blocked or channelled despite the high column loading at the high flow-rate.

Animals↗
PubMed1987

High performance liquid chromatographic determination of thromboxane B2 in human serum as a methoxime-panacylester derivative.

A high performance liquid chromatographic (HPLC) method was developed to measure thromboxane B2 (TxB2) levels in human serum. Serum samples (2 mL) were extracted using solid phase extraction columns in a C 18/silica mode sequencing approach. The internal standard, 6-ketoprostaglandin F1 alpha, was added to the serum extracts. The eicosanoids were doubly derivatized, first with panacyl bromide, then with methoxyamine to form methoxime-panacyl ester derivatives. The eicosanoid derivatives were chromatographed using a reverse phase HPLC system with UV detection (254 nm). Assay linearity was demonstrated with fortified TxB2 standards in 3% bovine serum albumin over a range of 25 to 500 ng/mL (r greater than or equal to 0.994). There was no significant interday difference or bias in assay results for pooled standards at 75, 226 and 376 ng/mL concentrations (p greater than 0.05). Pooled estimates of precision at these levels indicate an assay relative standard deviation 6-9%. The HPLC assay was used to quantitate TxB2 levels in human serum. Results were consistent with previously published values when drug-free serum was analyzed to assess ex vivo TxB2 formation.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Post-column reaction detection system for the determination of organophosphorus compounds by liquid chromatography.

The development and application of a post-column reaction detection system for organophosphorus compounds based upon their photodegradation to ortho-phosphate followed by the formation of reduced heteropolymolybdate is reported. Photodegradation occurs in a fused-silica tube coiled about a 450-W xenon lamp in the presence of ammonium peroxydisulfate. Photodegradation yields were practically quantitative for the organophosphates, -phosphonates, and -phosphorodithioates tested. Factors affecting the rate of the chromogenic reaction were optimized so that its contribution to the total band-broadening was negligible. The effect of interfering organic modifiers in the mobile phase was studied using the acetate ion as a model. Separations were developed using no organic solvents in the mobile phases. The determination of dialkylphosphates in urine and organophosphorus pesticides in tomatoes illustrate the potential of the methodology.

Animals↗
PubMed1972

A scanning x-ray microscope using synchrotron radiation.

Focused synchrotron radiation collimated by means of a pinhole has been used to construct a scanning x-ray microscope capable of making stereoscopic element-discriminating pictures of relatively thick specimens in an atmospheric environment.

Microscopy, Electron, Scanning↗