Spectrophotometric determination of lamotrigine in pharmaceutical preparations and urine by charge-transfer complexation

Rapid and sensitive spectrophotometric methods are developed for the determination of lamotrigine (LTG) in pharmaceutical dosage forms and urine samples, based on the formation of the charge-transfer (CT) complexes between LTG as an n-donor and the acceptors: bromocresol green (BCG), bromocresol purple (BCP), and chlorophenol red (CPR). These complexes are studied spectrophotometrically in chloroform solution in order to obtain some information about their stoichiometry and stability of complexation. The analytical parameters and their effects on the extraction of drug from urine samples are investigated. The reactions were extremely rapid at room temperature, and the absorbance values remained unchanged after 24 h for all reactions. Beer's law was obeyed in the concentration ranges 0.15–19.8, 0.15–19.8 and 0.05–34.1 μg · ml^–1 for CPR, BCP and BCG, respectively. The proposed methods were applied successfully for the determination of LTG in pharmaceutical formulations, and human urine samples in the presence of other antiepileptic drugs such as carbamazepine, oxcarbazepine and phenobarbital, with good accuracy and precision.