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The model compounds of Vitamin B₁ 3-benzyl-4-methylthiazolium bromide, (1), 3, 4-dimethylthiazolium iodide (2) and 2-(α-hydroxyethyl)-3-benzyl-4-methylthiazolium bromide (3) were prepared by the organic synthesis. Colorimetric determination with phosphotungstic acid showed an increase of 1.1∼1.2 folds with compound (1) and 1.5∼1.9 folds with compound (3) when readings were carried out after an overnight, compared with immediate readings. Colorimetry with 2.6-dibromoquinone chloroimide yielded the compound (1) being 2.2∼2.5 folds higher than the compound (3). The half wave potentials and diffusion currents of anodic and cathodic waves of polarography with the same concentration of the compounds (1), (2) and (3) also resulted in different values of their waves. Therefore, it was a firm conclusion that any values obtained from quantitative analysis with this model compounds (1), (2) and (3) were not directly applicable to those of Vitamin B₁.
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