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Biomedical subjects

H S Tan

Publications and source records attributed to H S Tan.

67 records · Page 4Linked to original sources
PubMed1976

Determination of coumarin and umbelliferone mixtures in whole blood by spectrophotofluorometry.

A spectrophotofluorometric method is described for the quantitative analysis of coumarin, umbelliferone, and mixtures thereof in whole blood. The two drugs were selectively isolated from blood by solvent extraction. Analysis of the isolated coumarin was based on the measurement of the fluorophore at activation and emission wavelengths of 361 and 491 nm, respectively. The fluorophore was obtained by irradiating an alkaline methanolic solution of the drug with UV light. A linear relationship between fluorescence and concentration existed over the concentration range of 0.02-0.2 mug of coumarin/ml. A mean recovery value of 94.8% was obtained from whole blood. The isolated umbelliferone was determined according to established methods at activation and emission wavelengths of 370 and 450 nm, respectively, and the limit of detection was 10 times more sensitive than previously reported. A linearity response was obtained between 1 and 10 ng of umbelliferone/ml. Good recovery data for mixtures of coumarin and umbelliferone in whole blood were obtained.

Coumarins↗
PubMed1976

Pharmacokinetics of coumarin upon i.v. administration in man.

The disposition pharmacokinetics of coumarin has been studied after i.v. administration in man, and might be described best by an open two-compartment model. Three dose sizes have been studied, 0.125, 0.2 and 0.25 mg/kg. The mean biological half-life was found to be 1.81, 1.45 and 1.49 h, respectively, for the three dose sizes. Coumarin is extensively distributed. The volume of the central compartment apparently comprises the extracellular and intracellular fluid. The study indicates dose-dependent (non-linear) pharmacokinetics with respect to distribution.

Adult↗
PubMedDate not supplied

Assay of citrate in pharmaceutical matrices by indirect photometric liquid chromatography.

The development of a simple HPLC procedure is described for the analysis of citrate in pharmaceutical formulations using the technique of indirect photometric chromatography. A novel mobile phase, using dual eluent species, was developed for rapid elution of citrate. The developed method was found to be linear over the range studied (1-12 micrograms of citrate injected), showed good per cent recoveries (+/- RSD) of 97.5 +/- 3.05% from a generalized matrix solution, and includes very simple sample preparation steps for analysis of commercial products. This method is quite specific for tricarboxylic acids as most other ions are not retained by the column using the developed mobile phase. The resolution of the method is also good as indicated by a baseline resolution (Rs = 1.5) obtained for citrate and tricarballylate, two structurally similar tricarboxylic acids. It is proposed that the developed method be evaluated as an alternative to the tedious procedures employed by the USP for assay of total citrate in some of its monographs.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Interfacial polymerization encapsulation of a viscous pigment mix: emulsification conditions and particle size distribution.

A viscous organic phase, containing up to 65 per cent solid pigment, was dispersed into water with an emulsifier by a rotor-stator homogenizer and the droplets formed were encapsulated by interfacial polymerization. Microcapsules with volume median diameters d50 ranging from 10 to 25 microns and geometric standard deviation (GSD), from 1.25 to 1.65, were obtained depending on emulsification conditions. Larger impellers gave smaller d50 and slightly narrowed GSD; d50 decreased and GSD increased as volume fraction of dispersed phase is decreased. Higher homogenizer speed and emulsifier concentration decreased d50 but slightly increased GSD. Increasing pigment content in dispersed phase decreased d50 but had little effect on GSD. These effects were assessed quantitatively by fitting an empirical model to the data.

Capsules↗
PubMedDate not supplied

Interfacial/free radical polymerization microencapsulation: kinetics of particle formation.

Microcapsules containing pigment and polymer were prepared by dispersing a viscous mixture of pigment, core monomers, initiators and oil-soluble shell monomer in an aqueous solution of surfactants, forming oil-in-water droplets. Subsequently, a water-soluble shell monomer was added to these droplets, encapsulating them via interfacial (IF) polycondensation. These microcapsules were then heated for free radical (FR) polymerization of the core monomers. Effects of primary variables, such as the shearing time during particle formation, surfactant concentration, organic phase concentration, and mode of water-soluble shell monomer addition, were studied. The results indicated that polyvinylalcohol (PVOH), used as the surfactant/stabilizer, reacted with the oil-soluble shell monomers. The depletion of PVOH, especially when PVOH concentration was low, resulted in rapid growth of particle size and, eventually, suspension failure. The kinetic data revealed a particle formation mechanism which consists of two processes. The first process is the formation of an equilibrium particle size by the equilibrium process of particle breakage due to the mechanical shearing force and coalescence due to collisions among particles and surface tension forces. The second process is the reaction between PVOH and oil-soluble shell monomer which leads to the depletion of PVOH and consequently causes more coalescence of particles and a significant increase in the equilibrium particle size. The net effect of these two processes shows an optimum shearing time where the smallest particle size can be attained, and this optimum time is a function of several primary variables. Methods to prevent the reaction and therefore the depletion of PVOH are proposed.

Amines↗