Application of Certain π-Acceptors for the Spectrophotometric Determination of Alendronate Sodium in Pharmaceutical Bulk and Dosage Forms

Two simple, fast, and accurate spectrophotometric methods for the determination of alendronate sodium are described. The methods are based on charge-transfer complex formation of the drug with two π-electron acceptors 7,7,7,8-tetracyanoquinodimethane (TCNQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile and methanol medium. The methods are followed spectrophotometrically by measuring the maximum absorbance at 840？nm and 465？nm, respectively. Under the optimized experimental conditions, the calibration curves showed a linear relationship over the concentration ranges of 2–10？μg？mL？1 and 2–12？μg？mL？1, respectively. The optimal reactions conditions values such as the reagent concentration, heating time, and stability of reaction product were determined. No significant difference was obtained between the results of newly proposed methods and the B.P. Titrimetric procedures. The charge transfer approach using TCNQ and DDQ procedures described in this paper is simple, fast, accurate, precise, and extraction-free. 1. Introduction Alendronate sodium is sodium trihydrogen (4-amino-1-hydroxybutylidene) biphosphonate trihydrate. It belongs to the bisphosphonate group and is used for the treatment of Paget’s disease of bone and osteoporosis, it diminishes bone resporption and thus reduces bone turnover [1, 2]. A survey of literature revealed that there are very few methods available for the determination of alendronate sodium. These methods include spectrophotometric [3–6], chromatographic [7–13], capillary electrophoresis [14], inductively coupled plasma [15], and voltammetric [16]. These previously reported spectrophotometric methods in the literature suffer from disadvantages like extraction, long time for the reaction to complete, narrow range of determination, and lack of sensitivity. Spectrophotometric techniques continue to be the most preferred methods for routine analytical work due to their simplicity and reasonable sensitivity with significant economical advantages. On the other hand, it is well known that p-benzoquinones such as 7,7,7,8-tetracyanoquinodimethane (TCNQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-electron acceptors often form highly colored electron-donor-acceptor (EDA) or charge transfer (CT) complexes with various donors which provides the possibility of determination of drugs by spectrophotometric methods [17, 18]. In order to develop new simple, fast, and extraction-free spectrophotometric methods for the determination of alendronate sodium in pure and pharmaceutical dosage forms, we investigated