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Physico-chemical methods for vitamin D assay and a new spectrophotometer Whittemore, Thomas Edwin

Abstract

The design and construction of a photoelectric spectrophotometer is described. The completed instrument has a wavelength reset accuracy of 1 A or less over the visible spectrum, and measures transmissions to 1 part in 500 with a bandwidth of 20-30 A. Suggestions for improved accuracy of transmission reading are included. The use of a controlled source makes an accuracy of 1 part in 10,000 theoretically attainable. This instrument was constructed so that vitamin D assay of low-potency oils could be attempted. Investigation of the antimony trichloride reaction by several authors showed that it was not suitable for this purpose. A preliminary investigation of the glycerol dichlorhydrin reaction was carried out with a Beckman model D spectrophotometer on several typical oils. It showed that this reaction was no more suitable than the other. Because of the instability of these reactions no method was found whereby increased instrument accuracy gave a corresponding increase in accuracy of assay. The only feasible method of assay for low-potency oils at present involves concentration of the vitamin D by chromatography.

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