Utility of some pi-acceptors for spectrophotometric determination of gatifloxacin in pure form and in pharmaceutical preparations

Four simple, quick and sensitive methods are described for the spectrophotometric determination of gatifloxacin. The methods are based on the reaction of gatifloxacin as n-electron donor with 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); chloranilic acid (CLA) and p-chloranil (CL) as pi-acceptors to give highly colored complex species. The colored products are quantitated spectrophotometrically at 460, 841, 530 and 545 nm for DDQ, TCNQ, CLA and CL, respectively. Optimization of the different experimental conditions is described. Beer's law is obeyed in the concentration ranges 5 - 60, 1.5 - 18, 30 - 360 and 20 - 240 mu g ml(-1) of gatifloxacin, but for more accurate analysis, Ringbom optimum concentration range was found to be 7.5 - 55, 3 - 16, 35 - 350 and 25 - 230 mu g ml(-1) of gatifloxacin for DDQ, TCNQ, CLA and CL, respectively. The limits of detection and quantification were calculated and the relative standard deviations for different concentrations of gatifloxacin using various acceptors were < 1.28\%. The association constants of 1 : I complexes and standard free energy changes using Benesi - Hildebrand plots were studied. The proposed methods were successfully applied to the determination of gatifloxacin in pharmaceutical dosage forms without interference from common additives encountered.