Indian Journal of Pharmacy Research, Dec 2013; 1(1):15-21 Nnadi Charles Okeke et.al, IJOPR 2013; 1(1) 15 Research Article Development of Differential Spectrophotometric Method for Assay of Paracetamol in Pure and Tablet Dosage Forms *C. O. Nnadi 1 , M. O. Agbo 1 , P. F. Uzor 1 , L. O. Ugwu 2 1. Department of Pharmaceutical and Medicinal Chemistry, University of Nigeria Nsukka, 410001 Enugu State. 2. Department of Veterinary Medicine, University of Nigeria, Nsukka, 410001 Enugu State. ABSTRACT A simple, sensitive, accurate and robust differential UV absorption spectrophotometric (DUAS) method for routine assay of paracetamol in pure and tablet dosage forms has been developed and validated in line with the International Conference on Harmonization (ICH) guidelines. The UV spectra of paracetamol was obtained separately in 0.1 N NaOH and HCl; assay of different tablet formulations was done by differential absorbance and the developed DUAS method subsequently applied for validation as per ICH guidelines. The overlain spectra showed maximum paracetamol absorption at 243.8 nm (maxima) and 255.6 nm (minima) in 0.1 N HCl and NaOH respectively. The developed method gave 99.5 to 100.2 % of the manufacturers’ claimed label content and recovery ȋaccuracy levelȌ of ͻͺ.ʹ ±ͳ.Ͳͻ ȋRSD ͳ.Ͳ5 %Ȍ to 102.4±2.19 % (RSD 0.93 %) of paracetamol in different selected tablet dosage forms. The standard Beer’s limit (and linearity range) was 1-20 µg/mL with R 2 value 0.992. Both intra- and inter-day precision showed % RSD< 2 while LOD and LOQ were 0.520 and 0.875 respectively. The developed DUAS method for assay of paracetamol is simple, accurate, precise, robust and reproducible with affordable and relatively safe inorganic solvents; and could be adopted in principles and practice for routine analysis of paracetamol in pure and pharmaceutical tablet formulations. Keywords: Differential, formulations, paracetamol, spectrophotometric, validation Received 21 Nov 2013 Received in revised form 14 Dec 2013 Accepted 16 Dec 2013 *Address for correspondence: Nnadi, Charles Okeke Department of Pharmaceutical and Medicinal Chemistry, University of Nigeria, Nsukka 410001 Enugu State. E-mail: chasnnadi@yahoo.com INTRODUCTION Differential ultra-violet absorption spectroscopy (DUAS) is an analytical technique based on the determination of changes in the absorption spectrum of ultra- violet-sensitive compounds by chemical modification such that components of the spectrum not affected by the modification are absent from the differential spectrum irrespective of how significant the components are to the absorbance of the UV- sensitive parent compound [1]. Major features of DUAS include well defined peaks ȋwavelength difference ≥ ͳͲ nmȌ for the spectra of both the parent and modified compounds, quantifiable intensity of the differential spectra and remarkably reproducible shape of the differential spectra. Many pharmaceutical products have been assayed by this method [2-20]. Paracetamol (PCM) also known as acetaminophen (Figure 1), an aniline derivative and a widely used over-the- counter (OTC) analgesic and antipyretic drug, is rarely classified as a non-steroidal anti inflammatory drug (NSAID) due to its weak anti inflammatory activity. It is used for the relief of headaches and other minor pains and can be combined with opioid analgesics in management of severe pains. HO N H H 3 C O Figure 1: Chemical Structure of Paracetamol (IUPAC name: N-(4- hydroxyphenyl) acetamide, molecular