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Biomedical subjects

W T Kok

Publications and source records attributed to W T Kok.

30 records · Page 2Linked to original sources
PubMed1989

Automated zone-electrophoretic sample treatment for the analysis of biological samples by high-performance liquid chromatography.

The automation of zone-electrophoretic sample treatment for liquid chromatography is described. The procedure is completely controlled from a liquid chromatograph. The carry-over of proteins from human serum under different experimental conditions was studied. The influence of the presence of proteins in the sample is illustrated with the anionic compound salicylic acid and the increase in selectivity for cationic compounds is demonstrated with the determination of ephedrine, norephedrine and amphetamine in urine.

Amphetamine↗
PubMed1986

Comparison of electrochemical detection methods in liquid chromatography for the determination of N-acetylcysteine in plasma.

Three electrochemical detection systems for the liquid chromatography of N-acetylcysteine in plasma have been compared: a dropping-mercury electrode detector, an amalgamated-gold electrode detector and a system in which iodine is generated electrochemically in the column effluent. The last detector approaches the reproducibility of the first (R.S.D. = 2%) and is as sensitive as the second, with a detection limit of 0.1 micrograms/ml plasma.

Acetylcysteine↗
PubMed1985

Analysis of neomycins A, B and C by high-performance liquid chromatography with post-column reaction detection.

The analysis of the antibiotics neomycins A, B and C was investigated. The separation of the components was studied using reversed-phase and reversed-phase ion-pair chromatography. The optimum separation was obtained utilizing a Lichrosorb RP-2 column with a mobile phase consisting of 75 mg/l sodium dodecyl sulphate, 0.5M Na2SO4 and 0.015 M sodium acetate buffer at pH 7.0. Using this mobile phase, baseline separation was obtained for all three compounds in approximately 20 min. Detection was via post-column derivatization of the analytes with ortho-phthalaldehyde in the presence of mercaptoethanol to form fluorescent iso-indole products. This system is applied to the analysis of a number of formulated products containing neomycin.

Journal Article↗
PubMed1983

Amperometric detection of amino acids in high-performance liquid chromatography with a copper electrode.

A copper electrode has been used as an amperometric detector for amino acids in high-performance liquid chromatography. The amino acids are separated in a reversed-phase system, using silica-based and polymer-type column materials. Neutral or alkaline buffer solutions of phosphate and carbonate can be used as mobile phases. Borate buffers are less suitable. The detection method is characterized by a high linear dynamic range, good reproducibility, the absence of electrode poisoning and a sensitivity comparable to that of UV absorption methods after derivatization of the amino acids. Detection limits with conventional-scale columns are in the range 10-100 pmoles. A reduction in the flow-rate in the flow-through cell improves the sensitivity for amino acids that give relatively low signals, such as proline. Therefore, the use of microbore columns is especially advantageous for these compounds. The absolute detection limits decrease by about one order of magnitude on changing to a miniaturized system.

Amino Acids↗