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VALIDATION STRATEGY APPLIED TO A POTENTIOMETRIC METHODDEVELOPED FOR DETERMINATION OF TOTAL FLUORIDE IN TOOTHPASTES.Caro YS, Santiago GM, Cámara MS, Robles JC, De Zan MM #Labora<strong>to</strong>rio de Control de Calidad de Medicamen<strong>to</strong>s, Facultad de Bioquímica y Cs. Biológicas, UniversidadNacional del Li<strong>to</strong>ralCC. 242, Ciudad Universitaria, 3000 Santa Fe, Argentina.INTRODUCTIONThe <strong>validation</strong> of new analytical procedures, i.e, the proof of its suitability <strong>for</strong> the intended purpose, is arequirement that have been clearly documented by regula<strong>to</strong>ry authorities. However the approach <strong>to</strong> <strong>validation</strong>is varied and opened <strong>to</strong> analyst interpretation (1). Several <strong>method</strong>ologies <strong>for</strong> chroma<strong>to</strong>graphic <strong>method</strong>s<strong>validation</strong> are available in literature, but not many <strong>for</strong> <strong>potentiometric</strong> procedures. Using the ICH guidelines asa basis we have selected the relevant parameters and acceptance criteria <strong>for</strong> designing experimental studiesneeded <strong>to</strong> validate a novel <strong>method</strong> <strong>for</strong> determination of <strong>to</strong>tal fluoride in <strong>to</strong>othpastes (2).MATERIALS AND METHODSSamples containing sodium fluoride (0.10%p/p) and monofluorphosphate (0.76%p/p) as active ingredientswere hydrolyzed with perchloric acid at room temperature and <strong>to</strong>tal fluoride was determined using an ionselective electrode (ISE) by a <strong>potentiometric</strong> <strong>method</strong> employing TISAB solution. In this procedure 1.4 g of<strong>to</strong>othpaste were suspended in 20.0 mL of deionized water and 25.0 mL of 70% p/p perchloric acid wereadded. Solution was stirred 15 min and diluted <strong>to</strong> 250.0 mL in volumetric flask after neutralization with 25.0mL of NaOH 10 mol L -1 . For <strong>potentiometric</strong> measures 2.00 mL of sample solution were diluted <strong>to</strong> 20.0 mLwith TISAB and solution potential was established with a fluoride ISE provided by OAKTON. TISABsolution was obtained by dissolving 58.5 g of NaCl, 61.4 g of sodium acetate and 0.30 g of sodium citrate in1.0L deionized water and adjusting pH <strong>to</strong> 5.5.The whole analytical procedure, including all the steps of the sample preparation, was <strong>applied</strong> in thedetermination of specificity, linearity, range, accuracy and precision. Spiking experiments <strong>for</strong> recovery andlinearity investigations were per<strong>for</strong>med in the whole working range using a synthetic mixture of matrixcomponents as placebo and standards of sodium fluoride and monofluorphosphate.RESULTSNo matrix components interferences were detected during specificity assays per<strong>for</strong>med by comparing averageresults of the response of reagents and placebo through a statistical t-test. Linearity was established in therange 4.0 <strong>to</strong> 12.0 mg L -1 by an F-test <strong>for</strong> residuals homoscedasticity and a lack of fit test.No statistical difference was obtained between the calibration set per<strong>for</strong>med with pure standard solutions andmatrix based calibration set, confirming the absence of “matrix effect”. Main recovery was not different from100 % at a 95% confidence level, with values ranging from 98.0 <strong>to</strong> 101.3% in spiked <strong>validation</strong> samplesobtained <strong>for</strong> lowest, medium and highest calibration levels. Repeatability and intermediate precision wereevaluated by applying an analysis of variance that showed no statistical difference between series per<strong>for</strong>medin sextuplicate <strong>for</strong> medium calibration level in difference days and by different analysts. Relative standarddeviation of the <strong>method</strong> resulted in 0.96%.CONCLUSIONSAn extended characterization and <strong>validation</strong> of the proposed <strong>method</strong> was carried out following internationalguidance obtaining excellent per<strong>for</strong>mance results. The procedure is simple, fast and efficient and may be<strong>applied</strong> in the routine quality control of <strong>to</strong>othpastes.# María Mercedes De Zan Tel/FAX: 54 342 4575205; e-mail: mmdezan@fbcb.unl.edu.ar


ACKNOWLEDGMENTSThe authors thank UNL <strong>for</strong> financial support from “Proyec<strong>to</strong> CAI+D 2009 Tipo II PI-12-62and Labora<strong>to</strong>rio LAFORMED S.A. <strong>for</strong> providing drugs and pharmaceuticalsREFERENCES(1) Ermer J.Validation in pharmaceutical analysis. PartI: An integrated approach.J Pharm Biomed Anal.2001;24:755-767(2) Norma Oficial Mexicana PROY-NOM-219-SSA1.2002.

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