Spectroscopic Fingerprinting of Aminoglycosides and Determination of Neomycin Sulphate Through Oxidative Ion-pair Complex Formation using Ammonium Molybdate

Background: Aminoglycosides are non-chromophoric antibiotics. The official method of assay in pharmacopoeias is microbiological. Bioassay methods are potency-semi-quantitative, laborious and time-consuming. In contrast, spectrophotometric methods are rapid, convenient, specific, sensitive and selective. The presence of NH2 and -OH functional groups in aminoglycosides makes them susceptible to redox reaction. Objective: A simple, cheap, quick, accurate and reliable spectrophotometric method for aminoglycoside analysis using neomycin as prototype via oxidation by ammonium molybdate reagent is proposed. Methods: Four aminoglycosides - amikacin, gentamicin, neomycin and streptomycin, were oxidized using ammonium molybdate (pH<2). These were scanned to obtain visible-spectrophotometric fingerprints. Two assay methods were developed. Method I involved the determination of the drug via the linear proportionality between neomycin and residual molybdate measured at 780nm and 850nm. Method II, an indirect determination using ion-pair reaction of excess molybdate and methyl orange measured at 430nm and 480nm. Results: All aminoglycosides formed blue complex, with distinct spectra peaks at 500nm, 640nm, 780nm and 850nm.The limit of detection and limit of quantification were from 0.33 to 2.32 μgmL-1 and 1.00 to 7.03 μgm L-1 respectively for both methods. Percentage recoveries ranged from 89.60 and 113.05 %, while precision and accuracy as RSD ranged from 0.23 to 3.55%. The regression coefficient (R2) ranged from 0.9968 to 0.9995. Percentage neomycin in dosage forms ranged from 95.67- 104.16% and 96.04 - 99.46% for methods I and II, respectively. Conclusion: The methods were successfully applied for neomycin sulphate determination in tablets and drops, therefore aminoglycosides could be assayed via the proposed methods.