Four rapid and sensitive methods for the assay of amoxycillin in pharmaceuticals using bromate-bromide mixture and two dyes

Four new methods using titrimetry and spectrophotometry are described for the rapid determination of amoxycillin in bulk drug and dosage forms. In direct titrimetry (Method A), the drug is titrated with bromate–bromide mixture in acid medium using methyl orange indicator. Back titrimetry (Method B) entails adding a known excess amount of bromatebromide mixture to the drug solution in acid medium, followed by determination of residual bromine iodometrically. Both spectrophotometric methods are based on the oxidation–bromination of amoxyciillin by in situ generated bromine followed by estimation of unreacted bromine with methyl orange (Method C) or indigo carmine (Method D) and measuring the change in absorbance at 520 or 610 nm. In all the methods, qunatitation is based on the amount of bromate that has reacted with amoxycillin. The experimental conditions have been optimized. Calculations are based on 1:1 and 1:2 (amoxycillin: bromate) stoichiometry for method A and Method B, respectively. Method A is applicable over 2-16 mg range, and 1-9 mg of amoxycillin could be determined by method B. In spectrophotometric methods, the absorbance is found to increase linearly with increasing concentration of amoxycillin which is corroborated by the calculated correlation coefficient (r) of 0.9964 (Method C) and 0.9959 (Method D). The calibration graphs are found to be linear over 0.1–1.2 and 0.5 – 4.0 μg mL for method C and method D, respectively. Method C with a molar absorptivity of 1.60 × 10 L mol cm is found to be more sensitive than method D (ε = 5.83 × 10 L mol cm). The limits of detection and quantification for both spectrophotometric methods are reported. Statistical evaluation of the methods was examined by determining intra-day and inter-day precisions. The methods were applied to the determination of amoxycillin pharmaceutical formulations. No interference was observed from excipients and the validity of the methods was tested against a reference method.