[Study on extractive spectrophotometry for determination of amoxicillin with ionic associate].

A method of extractive spectrophotometry has been proposed for the determination of amoxicillin (AMO). The ion pairs complex of amoxicillin with methylene blue (MB) can be extracted into 1,2-dichloroethane at pH 3.3 and has absorption maximum at 657 nm. The ratio of amoxicillin to methylene blue in the ion pairs complex is 1:1. The apparent molar obsorptivity of ion pairs complex is 5.0 x 10(4) L x mol(-1) x cm(-1) at 657 nm. The calibration graph generated is linear over the range of 0.4-6.8 mg x L(-1) drug in solution with a correlation of 0.9989. The detection limit is 0.01 mg x L(-1) and the recovery of AMO is 97.5%-101.3%. The present method has been applied to the determination of amoxicillin in pharmaceutical formulations and urine samples with satisfactory results.