Analele UniversităŃii din Bucureti – Chimie (serie nouă), vol 19 no. 1, pag. 61 – 68 © 2010 Analele UniversităŃii din Bucureti INDIRECT SPECTROPHOTOMETRIC DETERMINATION OF NEOMYCIN BASED ON THE REACTION WITH CERIUM (IV) SULFATE Iulia Gabriela David  , V. David  , A. A. Ciucu  and Adela Ciobanu  abstract: A simple and sensitive spectrophotometric method has been described for the assay of neomycin either in pure form or in pharmaceutical formulations. The proposed method was based on the oxidation of the studied drug by a known excess of cerium (IV) sulfate in acidic medium and estimating the unreacted oxidizing agent by adding a known amount of methyl orange in the same acid medium and measuring the absorbance of the resulted solution at λmax=498 nm. Different variables affecting the reaction were studied and optimized. Beer’s law is obeyed in the concentration range of 1 10 36 and 1.3 10 35 M and the detection limit of the method was 4.7 10 37 M neomycin. The proposed method was applied successfully to the determination of the examined drug either in a pure or pharmaceutical dosage forms with good precision. No interferences were observed from excipients and the results obtained were in good agreement with those obtained using the official method. key words: neomycin; spectrophotometry; cerium(IV) sulfate; redox reaction; pharmaceutical formulations. received: April 27, 2010 accepted: June 01, 2010 1. Introduction Neomycin [(1R,2R,3S,4R,6S)34,63diamino323 {[33O3(2,63diamino32,63dideoxy3β3L3 idopyranosyl)3β3D3ribofuranosyl]oxy}333hydroxycyclohexyl 2,63diamino32,63dideoxy3α3 D3glucopyranoside] (Fig. 1) (NOM), is a broad spectrum aminoglycoside antibiotic widely used in clinical therapy of serious infections. It inhibits the growth of both gram3positive and gram3negative bacteria. Many analytical techniques have been employed for the detection and determination of neomycin and other aminoglycoside antibiotics including potentiometry [1] voltammetry, [2÷6], amperometry [7], fluorometry [8÷12], electrophoresis [13÷16], spectrophotometry [17÷20], chromatography [21÷ 27], and immunoanalysis [28].  University of Bucharest, Faculty of Chemistry, Department of Analytical Chemistry, Romania corresponding author email: i_g_david@yahoo.com  University of Medicine and Pharmacy – Carol Davila, Department of Psychiatry, Bucharest, Romania Department of Physical Chemistry 4312 Regina Elisabeta Blvd, District 3, Bucharest phone: +4032133143508; fax: +4032133159249 pISSN: 12203871X eISSN: 184430401 ARS DOCENDI PUBLISHING HOUSE Sos. Panduri 90, District 5 Bucharest phone/fax: +4032134102575 e3mail: arsdocendi@yahoo.com