An effective application of the spectrophotometric and thermodynamic methods have been described for the determination of thiamine hydrochloride. The spectrophotometric method was based on charge transfer complexation reaction using thiamine as  n-electron donor and 2, 3 dichloro-5,6-dicyano -1,4-benzoquinone (DDQ) as a π-acceptor to form a highly coloured species  with 1:1 stoichiometric ratio. The coloured product was quantified spectrometrically at 474nm under the established experimental conditions.  Beer’s law was obeyed over the concentration ranges of 5-80μg/ml. The Apparent molar absorptivity was calculated to be 1.08 x 103Lmol-1cm-1with the corresponding Sandell sensitivity of 2.68. The Ross equation was used for studying the thermodynamic parameters and result reveals that ∆S was calculated to be between 67.13J/mol and 66.70J/mol, ∆H = -2.87kJ/mol. The association constants were found to decrease from 30°C to 60°C with increase in molar absorptivity.  Also high values of association constant were seen which ranged from 500Lmol-1cm-1to 1667Lmol-1cm-1. The proposed methods were applied successfully to the determination of thiamine hydrochloride in pure and commercial forms with average recovery of 96.2% ± 0.016. Statistical comparison of the results were performed using student’s t-test and f-test at 95% confidence level.

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