Vitamin methods

DURING the past two years a systematic study has been made in this laboratory of the various possible sources of error and the technical difficulties involved in the thiochrome test, based on the now well-known reaction first described by Jansen [1936]. These errors and difficulties are more serious than is generally appreciated. In an earlier paper [Wang & Harris, 1939] a procedure was described for urine, by which-interference from non-specific substances and various other problems of technique were successfully overcome. Our results were controlled by biological tests, and this proof of the reliability of the method applied to urine has been further confirmed since [see accompanying paper, Harris & The present communication describes how the technique used by Wang & Harris mtny be adapted for estimating vitamin B1 in foodstuffs and in animal and plant tissues. As we have again repeatedly checked our results by biological assays, we feel considerable confidence in the method which we are now recommending.