A Charge Transfer Method for the Determination of Thiamine Hydrochloride Using 2,3- dichloro-1,4-dicyano-5,6-benzoquinone

Aims: The aim of this research is to determine a method based on the formation of charge transfer complex between thiamine and 2,3- dichloro-1,4-dicyano-5,6-benzoquinone (DDQ) that is simple, fast, economical and less laborious.

Objectives: To establish the degree of charge transfer complex formation between thiamine and DDQ, to determine the stability of the charge transfer (CT) complex with respect to time, temperature and pH. To apply the charge transfer complex in spectrophotometric determination of the drug, to determine the average recoveries of the drug in pure and commercial forms, to validate the proposed method using International Conference on Harmonization Guideline.

Study Design: A simple and sensitive spectrophotometric method.

Place and Duration of Study: Department of Chemical Engineering, Faculty of Engineering and Technology, Madonna University Nigeria, Akpugo campus) Enugu state, Nigeria and Department of pure and Industrial Chemistry, Faculty of Physical Sciences, University of Nigeria, Nsukka, Nigeria between January 2013 and November 2015.

Methodology: Transfer serial volumes of 0.036, 0.04 …… to 0.32 ml in 0.004 step of the standard thiamine (0.001 g/ml) solution equivalent to 5 µg/ml-80 µg/ml to different test tubes. Added 0.2 ml of buffer 8 to each test tube. Finally, add calculated volumes of DDQ (0.001 g/ml) solution in methanol to the content, mix and allow standing for 25 min at 40°C before analysis at 474 nm against a methanol blank using an ultraviolet, visible spectrophotometer. Two thiamine hydrochloride tablets were grinded on a mortar. An amount equivalent to 0.01 g was weighed and dissolved in some methanol. It was stirred to extract the active ingredient, filtered with What man no. 1 filter paper and made up to 10 ml to give a theoretical 0.001 g/ml concentration. Similar volumes were transferred to different test tubes and prepared as described in the general procedure before analysis at 474 nm.

Results: A simple and sensitive spectrophotometric method is described for the assay of thiamine. The method is based on charge transfer complexation reaction of thiamine as n-electron donor with 2, 3 dichloro-5,6-dicyano -1,4- benzoquinone (DDQ) as -acceptor to give highly coloured species with 1:1 stoichiometric ratio. The coloured product was quantified spectrometrically at 474nm under the optimized experimental conditions. Beer’s law is obeyed over the concentration ranges of 5-80μg/ml. Formation and stability of the complex of thiamine were optimum at pH 8. The Apparent molar absorptivity was calculated to be 1.08 x 103Lmol-1cm-1 with the corresponding Sandell sensitivity of 2.68. Limit of detection and quantification of the drug based on this method were thiamine 1.23 and 3.37 respectively.

Conclusion: The proposed method was applied successfully to the determination of thiamine hydrochloride in pure and commercial forms with an average recovery of 96.2% and SD = 0.016. Statistical comparison of the results was performed using student’s t-test and f-test at P = .05 confidence level.