Journal of American Science 2013;9(7) http://www.jofamericanscience.org Reducing power evaluation of antioxidant drugs by potentiometric titration A.M. El-Kosasy, L. A. Hussien and M. H. Abdel-Rahman Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Ain Shams University, Abbassia, 11566 Cairo, Egypt [email protected] Abstract: An accurate and precise potentiometric automatic titration technique is applied based on redox reaction between reducing drugs (Paracetamol and dl methionine) as antioxidants and standard potassium permanganate as an oxidizing agent, which is employed in acidic medium. The titration is monitored with a Platinum indicator electrode and carried out until the greatest jump of potential from one drop of titrant appears. %RSD values were 1.12 for Paracetamol and 1.336 for dl methionine. The proposed method was successfully applied for the determination of Paracetamol in pharmaceutical formulation with accuracy 101.50 ± 0.985%. The method was robust to deliberate changes in temperature (30⁰C ± 5). Paracetamol was found to be more reducing to potassium permanganate than dl methionine. [A.M. El-Kosasy, L. A. Hussien and M. H. Abdel-Rahman. Reducing power evaluation of antioxidant drugs by potentiometric titration. J Am Sci 2013; 9(7): 114-118]. (ISSN: 1545-1003). http://www.jofamericanscience.org. 13 Keywords: antioxidant, titration, Paracetamol, Potentiometric, platinum. 1. Introduction: cysteine and taurine which protect the cells from Paracetamol and dl methionine are antioxidant oxidative damage and play vital role in preventing cell drugs. Paracetamol reduces aspirin-induced gastric detoxification7 In addition, dl methionine has been mucosal injury. The gastroprotective effect of shown to chelate lead and remove it from Paracetamol is comparable to the protective effect of tissues8.Homocysteine (Hcy), a thiol formed by PGE2 on gastric mucosa and is accompanied by demethylation of DL methionine is, at moderately significant decrease of the gastric lipid peroxidation high levels, a known independent risk factor for (evaluated as MDA-generation)1. It reduces the atherosclerosis and increased vascular dysfunction9. amount of lipid peroxides generated in LDL during However, it displays an antioxidant effect on cellular mononuclear cell–mediated oxidation by 69%. Maritet systems at micromolarlevels10.Also, L-methionine al.2 indicated that Paracetamol protects LDL against leads to a concentration-dependent induction of the Cu2+-induced, azo compound–initiated, and antioxidant proteins heme oxygenase-1 (HO-1) and mononuclear cell–mediated oxidative modification in ferritin in cultured endothelial cells11.The radical vitro and that this may be due to the radical scavenger scavenging activity of methionine has been reported in capacity of Paracetamol which was tested by using literature using hydroxyl radical scavenging assay12,13. Diphenyl picryl hydrazyl radical scavenging activity, For d methionine it is considered as a superoxide also, Paracetamol protects erythrocytes from oxidative radical suppressor14. In the work presented here, a stress3,4. Paracetamol significantly reduces KCN- novel electrochemical method for evaluation of induced superoxide anion generation as well as KCN- antioxidant activity is proposed. An automatic titration induced lipid peroxidation, it was found that technique based on redox reactionis pursued by means Paracetamol has the potential to limit the undesirable of potentiometry. Platinum indicator electrode is effects of superoxide anion5.It is an efficient inhibitor applied whose potential changes markedly at the of potent oxidants hypochlorous acid (HOCl) and equivalence point which is easily obtained from the hypobromous acid (HOBr) from halide ions generated titration curve by applying first and second derivative by isolated heme peroxidase enzyme myeloperoxidase where the first derivative, ΔE/ ΔmL is maximal and its which released by activated neutrophils and second derivative Δ2E/ ΔmL2equals zero. The monocytes. These oxidants have been implicated as reducing power of Paracetamol and dl methionine key mediators of tissue damage in many human could be determined by this method by calculating inflammatory diseases including atherosclerosis, number of electrons obtained by one molecule of the asthma, rheumatoid arthritis, cystic fibrosis and some two studiedantioxidant drugs. Potassium cancers6.Dl methionine is a precursor amino acid for permanganate acts as an oxidizing agent in acidic important antioxidant molecules such as glutathione, medium by the following equation15: 114 Journal of American Science 2013;9(7) http://www.jofamericanscience.org 2. Experimental permanganate, in triplicates under the specified 2.1. Instrumentation conditions, within the same day, In order to evaluate Mettler Toledo automatic compact titrator model the degree of method repeatability, the mean G20 with Labx software version 3.1 with reference percentage recoveries and the relative standard electrode. Platinum wire deviations were then calculated. 2.2. Samples 2.3.1.2.b. Intermediate Precision 2.2.1. Pure samples The interday variation was evaluated on above Pure Paracetamol and dl methionine was kindly mentioned concentrations of each drug for three supplied by HIKMA Pharmaceutical Company (6th successive days, and then the mean percentage October, Egypt). recoveries and the relative standard deviations were 2.2.2. Market samples calculated. Abimol tablets, batch no., were manufactured by 2.3.1.3. Robustness GSK Company (Cairo, Egypt). Robustness was studied by applying small 2.2.3. Chemicals and Reagents: deliberate changes in temperature (30⁰C ± 5) during Potassium permanganate (0.025 N), (Adwic) the method developing for concentration (0.4 mg/ mL) prepared according to European Pharmacopoeia16. The for each drug, separately. The % RSD was then stock solution was standardized with oxalic acid and calculated. was prepared daily. Diluted sulfuric acid (10% v/v) 2.3.2. Application to Pharmaceutical formulations (Adwic). The suggested procedure was applied for the 2.2.4. Standard solutions: analysis of Paracetamol in Abimol® tablets, where the Stock standard solutions contents of ten tablets were weighed, powdered and Paracetamol (2.00 mg/mL) mixed. An amount of the powder equivalent to 100 mg It was prepared by accurately weighing pure of Paracetamol was transferred to 250 ml beaker. The sample equivalent to 200.00 mg paracetamol into 100- powder was extracted with 50 ml water and filtered mL volumetric, dissolved in and diluted to the volume into clean 100 ml volumetric flasks, washed and then with water. completed to mark to prepare 1mg.ml-1 Paracetamol. Dl methionine (2.00 mg/mL) The method stated under accuracy is then repeated. It was prepared by accurately weighing pure Standard addition technique was applied to assess the sample equivalent to 200.00 mg DL methionine into accuracy of the proposed method by spiking different 100-mL volumetric, dissolved in and diluted to the known concentrations of pure Paracetamol to the volume with water. pharmaceutical preparation. The procedure described 2.3. Procedure under the assay of Abimol® tablets was followed. A potentiometric titration procedure using Concentrations were calculated; the mean percentage Mettler Toledo automatic compact titrator is recoveries and the relative standard deviations were established by immersing a reference electrode and a then calculated. highly folded platinum wire as an indicator electrode 3.Results and Discussion which are connected to the titrator in the titration 3.1. Proposed reaction products vessel where ten mL of the solution of drug under The power of certain antioxidants is associated study is added to 20 mL diluted sulfuric acid, the with their reducing power17.The proposed titrant used is 0.025 N potassium permanganate. potentiometric titration procedure is based on redox 2.3.1. Method validation reaction between the studied antioxidant drugs and 2.3.1.1. Accuracy standard potassium permanganate in acidic medium. Ten milliliters of different working solutions For Paracetamol, the stoichiometry of the reaction of (0.40-2.00 mg/mL) of Paracetamol and dl methionine Paracetamol with permanganate in sulphuric acid separately, were titrated against standard potassium proved to be 1:2, respectively18 and it’s apparent from permanganate (0.025 N), in triplicates, the specified previous equation that each mole of potassium conditions were set. After obtaining the end-point for permanganate needs five electrons to be reduced in each one, the average concentrations were calculated acidic medium so Paracetamol will produce ten using the law of concentration and the percentage electrons for the redox reaction to be settled. For DL recoveries were calculated. methionine, it had been reported that dl methionine in + 2.3.1.2. Precision acidic medium (C5H12NO4S ) is oxidized by oxidizing 2.3.1.2.a. Repeatability agent leading to the formation of methionine sulfoxide 19 Three samples of concentrations 0.40, 0.60, 0.80 (C5H11NO3S) species . The following equation mg/mL of pure Paracetamol and dl methionine represents the proposed half equation reaction: separately, were titrated against standard potassium 115 Journal of American Science 2013;9(7) http://www.jofamericanscience.org + + + C5H12NO2S + H2O C5H12NO3S + 2H + 2e The equivalent factor is calculated as follows20: F = [Equivalent weight of sample drug X Normality of the standard] /1000 Where Equivalent weight of sample drug = Molecular weight