DRUGS, COSMETICS, FORENSIC SCIENCES Simultaneous Spectrophotometric Determination of Paracetamol and Salicylamide in Human Serum and Pharmaceutical Formulations by a Differential Kinetic Method ALI REZA ZAREI Malek-Ashtar University of Technology, Faculty of Materials & Chemical Engineering, Tehran, Iran ABBAS AFKHAMI 1 and NAHID SARLAK Bu-Ali Sina University, Department of Chemistry, Faculty of Sciences, Hamadan, Iran A rapid, simple, and sensitive differential kinetic method is presented for the determinations of acetaminophen (also known as paracetamol) and salicylamide. The method is based on their oxidation reaction by Fe 3+ ion in the presence of 1,10-phenanthroline as indicator. The reactions can be monitored spectrophotometrically by measuring the increase in the absorbance of the solution at 510 nm. Two times were selected one in which only paracetamol is oxidized by Fe 3+ ion and the other in which both drugs are oxidized by Fe 3+ ion. The data were evaluated by the proportional equations method. The method allowed the simultaneous determination of paracetamol and salicylamide at concentrations between 0.5–20 and 1–40 mg/mL with relative standard deviations of 3.47 and 2.58%, respectively. The method was applied to the simultaneous determination of paracetamol and salicylamide in human serum and pharmaceutical formulations. P aracetamol (N-acetyl-p-aminophenol, acetaminophen) and salicylamide (o-hydroxy benzamide) have been widely used as analgesic and antipyretic drugs. Several methods have been reported for the determination of paracetamol in pharmaceuticals based on different techniques. These include volumetry (1), spectrophotometry (2–14), chronoamperometry (15), spectrofluorometry (16), and chromatography (17, 18). Salicylamide has analgesic and antipyretic effects similar to those of salicylates. Its therapeutic action and potential toxicity are still the subject of research, which makes it necessary to control its presence in biological fluids. Several methods have been reported for the determination of salicylamide in biological fluids. These include synchronous fluorescence spectroscopy (19, 20), chromatography (21), spectrophotometry (22), spectrofluorometry (23), first-derivative matrix isopotential synchronous fluorescence (MISF;24) and flow-injection chemiluminescence (25). Several reports on the simultaneous determination of paracetamol and salicylamide in mixtures have also been published. These include column liquid chromatographiy (17, 26), spectrophotometry (27–29), polarography (30), and first-derivative spectrofluorometry (31). Recently, we reported the simultaneous spectrophotometric determination of salicylamide and paracetamol by the H-point standard addition method (HPSAM) and partial least squares (PLS) calibration (32). Differences in kinetic behavior have been used extensively for the simultaneous determination of 2 or more components in mixtures. Many differential kinetic methods have been proposed for the analysis of mixtures of closely related species without prior separation. The proportional equation method is a mathematical method with wide use in differential kinetic methods for the resolution of closely related species. This method depends on changing the ratio of 2 rate constants by varying the reaction medium or the conditions (33). In this paper, we describe a simple, precise, and accurate differential kinetic method for the spectrophotometric determination of paracetamol and salicylamide in mixtures. The method is based on their oxidation reaction with Fe 3+ ion. The complex formation between produced Fe 2+ ion and 1,10-phenanthroline at pH 4.5 is used as the indicator reaction. Experimental Apparatus A Pharmacia Biotech (Cambridge, UK) Model LKB3 UV-visible Ultraspect(III) single beam spectrophotometer connected to a Pentium II computer with 1 cm quartz cells was used for absorbance measurements. All spectral measurements were performed using the blank solution as a reference. Measurements of pH were made with a Jenway Ltd. (Dunmow, Essex, UK) C15 pH meter using a combination glass electrode. ZAREI ET AL.:JOURNAL OF AOAC INTERNATIONAL VOL. 88, NO. 6, 2005 1695 Received February 8, 2005. Accepted by JM March 29, 2005. 1 Author to whom correspondence should be addressed: e-mail: afkhami@basu.ac.ir Downloaded from https://academic.oup.com/jaoac/article-abstract/88/6/1695/5657396 by guest on 25 July 2020