抄録
Thiamine, added to series of borate-KCl-NaOH buffers between pH 7 and 12.5,was determined as thiochrome by the following procedures : (a) immerdiately, (b) after standing for 1 hour at 30℃, and (c) after standing for 1 hour at 30℃ and then acidifying the solution by HCl, all using ferricyanide-NaOH or (d) after standing with ferricyanide for 1 hour at 3O℃, then adding NaOH to it. The formation of thiochrome was observed as (a) 100% all over the ranges, (b) sharp decrease between pH 9 and 10,then 0% beyond pH 10.5,(c) the least yield at pH 9.6,while 100% at pH 7 or 12.5 and (d) gradual decrease between pH 8 and 11. The similar determination of thiamine using cyanogen bromide instead of ferricyanide was carried out by the procedures (a)〜(d) : The formation of thiochrome was shown to be similar in the cases of (b) and (c) but different in the cases of (a) and (d) which both indicated sharp decrease between pH 10 and 11 then 0% beyond pH 12. The decomposition of thiamine at pH 9.6 in (c) was proved to be its oxidation to thiamine disulfide which was recovered as thiamine by cysteine-treatment.
