Acta Pharm. 59 (2009) 407-419
Original research paper
A new approach to the spectrophotometric
determination of metronidazole and tinidazole using p-dimethylaminobenzaldehyde
OLAJIRE
AREMU ADEGOKE and OFFIONG EDET UMOH
jireade@yahoo.com, ao.adegoke@mail.ui.edu.ng
Department
of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Ibadan, Ibadan,
Nigeria
Accepted September 28, 2009
A new approach to the spectrophotometric determination of metronidazole (MZ) and tinidazole (TZ) has been developed. The procedure involves coupling of diazotized nitroimidazoles with p-dimethylaminobenzaldehyde (DMAB) to form a greenish-yellow solution. Optimal temperature and time for diazotization were 0 oC (iced) and 3 minutes and 30 oC and 2 minutes for coupling was, respectively, for both MZ and TZ. Coloured adducts of MZ and TZ showed peaks at 406 nm and 404 nm, respectively, which were selected as analytical wavelengths. The reaction with p-DMAB occurred in a 1:1 mole ratio. Beer’s law was obeyed within the 4.8–76.8 µg mL-1 concentration range with low limits of detection. The azo adducts were stable for over a week. Molar absorptivities were 1.10 x 103 (MZ) and 1.30 x 103 L mol-1 cm-1 (TZ). Overall recoveries of MZ and TZ from quality control samples were 103.2 ± 1.3 and 101.9 ± 1.3 % over three days. There was no interference from commonly utilized tablet excipients. No significant difference was obtained between the results of the new method and the BP titrimetric procedures. The azo approach using the p-dimethylaminobenzaldehyde procedure described in this paper is simple, fast, accurate and precise. It is the first application of DMAB as a coupling component in the diazo coupling reaction.
Keywords: nitroimidazoles, diazotization, spectrophotometry, p-dimethylaminobenzaldehyde