Microdetermination of ergocalciferol (vitamin D2) in pharmaceutical preparations by differential spectroscopy using trifluoroacetic acid in the absence of vitamin A.
A differential spectroscopy method for the determination of microgram quantities of ergocalciferol, using trifluoroacetic acid and hydrogen peroxide, was applied to commercially available pharmaceutical preparations. Tablets were powdered and extracted with methanol after being made basic with diethylamine. The methanol was concentrated, chloroform was added, and the mixture was chromatographed on neutral alumina using chloroform as the eluent. Ergocalciferol was determined in an aliquot of the eluate by differential spectroscopy and was compared with a reference ergocalciferol standard treated similarly. The method applied to low potency formulations (2.5-6 mug/tablet) is simple and quantitative, needs less than 5 hr for completion, and has a precision of less than +/- 2%. A simple and accurate chromatographic method for the determination of ergocalciferol in stabilized powders and high potency tablets, which precludes the necessity of solvent-solvent extraction, was also developed. The results are comparable with those obtained by the rat bioassay and the USP XVIII chemical assay.
Quality Control Methods for Group D Vitamins
Determination of the content of vitamin D is a rather difficult problem. In the present study, we have compared methods that are most widely used for determining group D vitains. In recent years, physical and chemical methods of analysis have found increasing use due to their simplicity, sensitivity, and information value. Various methods of quality control are currently used but the future in the analysis of calciferols undoubtedly belongs to HPLC. This method is capable of simultaneously solving all problems encountered in the analysis of group D vitamins.
Coated-wire electrodes containing polymer immobilized ionophores blended with poly(vinyl chloride).
Polymers containing covalently attached 18-crown-6 or 2.2.2 cryptand units were incorporated into plasticized PVC membranes and the composite membranes were examined as potassium ion sensor elements. Ionophores were linked to carboxy-PVC and to poly(acrylic acid) via amide linkages to an alkyl spacer unit. Coated-wire electrodes (CWEs) from the immobilized ionophores gave acceptable responses, but conventional ion-selective membrane electrodes (ISEs) prepared by solvent casting were inactive. Dip-cast membranes did give active ISEs. Potassium electrode performance was independent of the loading of the ionophore within the acrylate support polymer, but depended upon the spacer length. Ion selectivity varied with the ionophore loading within the support polymer. Selectivity is a composite of the ionophore selectivity and ion-exchange interactions with the acrylate backbone, giving selectivities akin to carboxylate substituted crown ethers, notably enhanced monovalent/divalent ion discrimination relative to the ionophore in solution. Polymer immobilization extended the lifetime of active electrodes.