Vitamin methods

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Abstract
An accurate procedure, based on the method of Wang and Harris (1939) for urine, was worked out. Special features included a preliminary process of extraction; digestion with papain and takadiastase for conversion of cocarboxylase into aneurin, breaking down proteins, polysaccharides, etc., and removing inhibitors; washing of the digest with isobutanol to remove interfering substances, omission of adsorption because it caused variable losses; conversion to thiochrome in presence of methanol, and with addition of the K4Fe(CN)6 prior to the NaOH in order to protect against loss by oxidation; washing of the thiochrome layer with water to permit accurate differentiation between cocarboxylase and free vit. B1, and to eliminate non-specific fluorescent substances and pigments; and visual comparison of fluorescence with the aid of light-filters and blank controls. To test the reliability of the method, systematic comparisons with biological tests were carried out on over 50 foodstuffs. The agreement was good, the products examined covering the wide range of activities of 200 to 0.03 I.U. per g. In 75% of instances the biological and chemical values differed by less than 15%, or in 87% of instances by less than 30%; the larger % errors were found only with foods poor in the vit., or with a group of desiccated products which were difficult to extract. Where there were detectable differences the trend was for the chemical values to be lower than the biological (avg. difference =[long dash]6%). With 0.1 ug. of aneurin per ml. chemical results were duplicated with an error of about [plus or minus] 5% and with 0.03 ug. per ml. with an error of [plus or minus] 10%. The procedure is easy to work, and upwards of 20 specimens can be examined in a working day. Erroneously low values given by certain other modifications of the thiochrome test are explained.