Spectroscopic study of charge transfer complexation between doxepin and π–acceptors and its application in quantitative analysis

Add time:07/27/2019    Source:sciencedirect.com

Charge transfer complexes of the doxepin with π – acceptors such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ) and p-chloranilic acid (p-CA) have been studied spectrophotometrically. The stoichiometry of the reactions was studied by Job's method of continuous variations which show that the complexation ratio was 1:1 (acceptor: donor) for DDQ, TCNQ and p-chloranilic acid with doxepin base. The data were discussed in terms of association constant (K), molar absorptivity (ε), free energy change (ΔG), oscillator strength (f), transition dipole moment (μEN), resonance energy (RN) and ionization potential (ID). Three simple, fast and sensitive spectrophotometric methods were proposed for the quantification of doxepin hydrochloride in pure form and drug formulations. The methods (A, B and C) were based on the reaction of doxepin base as n-donor with DDQ, TCNQ and pCA resulting in coloured species which absorbed maximally at 570 nm, 840 nm and 530 nm, respectively. Beer's law was obeyed in the concentration range of 5–45 μg mL− 1, 40–360 μg mL− 1, and 40–400 μg mL− 1 for the methods A, B, and C, respectively. A series of variables were studied to optimize the reaction conditions. The developed methods were successfully applied for the determination of doxepin in its formulations with high accuracy and precision and without interference from common excipients.

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