Spectrophotometric determination and thermodynamic studies of the charge transfer complexes of bambuterol–HCl

Objective

The aim of the present work was to develop simple spectrophotometric methods for the simultaneous determination of bambuterol hydrochloride.

Method

Spectrophotometric method for determination of bambuterol hydrochloride after its conversion to bambuterol base by formation of charge transfer complexes as n-donor with π-acceptors, dichlorodicyanobenzoquinone (DDQ) and tetracyanobenzoquinodimethane (TCNQ) which were prepared in acetonitrile. They yield radical anions measured at 461 and 842 nm within concentration ranges of 36.7–183.7, 4.59–36.7 μg ml⁻¹ with a good correlation coefficients (r² = 0.9999–0.9998) respectively. The nature of the formed complexes was studied via determination of the association constant and the molar absorptivity using Bensi–Hildebrand equation. The free energy change (ΔG) and the enthalpy of formation (ΔH) as well as the entropy (ΔS) were determined for the reaction product with TCNQ. The method was successfully applied for the analysis of bambuterol hydrochloride in its pharmaceutical preparation where no interference could be observed from the additives commonly present as proven by good mean recoveries of 99.74% and 100.014%. There was no significant difference observed when the method was statistically compared with the pharmacopeial official method used for determination.

Conclusion

The proposed charge transfer complexation methods are rapid and simple and from the economical point of view, the analytical reagents used are inexpensive, have excellent shelf life and are available in any analytical laboratory. The suggested methods could be successfully applied for quality control and routine analysis.