Studies on the isomerization of vitamin D and related componds with acidic reagents. I. A simple method for the determination of vitamin D2 isomers in mixtures

Vitamin D3 in plasma: quantitation by mass fragmentography

Combined gas chromatography-mass spectrometry with multiple-ion detection is used to quantitate vitamin D3 in plasma samples. Extensive cleanup of the plasma extract prior to analysis is required before mass fragmentographic analysis is possible, i.e., solvent extraction, digitonin precipitation, Lipidex column chromatography, and derivatization. Low resolution mass fragmentography is performed by monitoring simultaneously the molecular ions of the heptafluorobutyric esters of the all-trans isomer of vitamin D3 and dihydrotachysterol2, which is used as an internal standard. This new method uses 5 ml of plasma and it is specific and sensitive to 600 pg of vitamin D3. This assay shows that in plasma of normal adult subjects there is a vitamin D3 concentration of 5 to 11 ng/ml, lower than those values reported for biological and competitive protein binding assays. Specifically the method described offers potential as an eventual reference method.

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.