validation strategy applied to a potentiometric method developed for ...

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 #Laboratorio de Control de Calidad de Medicamentos, Facultad de Bioquímica y Cs. Biológicas, UniversidadNacional del LitoralCC. 242, Ciudad Universitaria, 3000 Santa Fe, Argentina.INTRODUCTIONThe validation of new analytical procedures, i.e, the proof of its suitability for the intended purpose, is arequirement that have been clearly documented by regulatory authorities. However the approach to validationis varied and opened to analyst interpretation (1). Several methodologies for chromatographic methodsvalidation are available in literature, but not many for potentiometric procedures. Using the ICH guidelines asa basis we have selected the relevant parameters and acceptance criteria for designing experimental studiesneeded to validate a novel method for determination of total fluoride in toothpastes (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 total fluoride was determined using an ionselective electrode (ISE) by a potentiometric method employing TISAB solution. In this procedure 1.4 g oftoothpaste 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 to 250.0 mL in volumetric flask after neutralization with 25.0mL of NaOH 10 mol L -1 . For potentiometric measures 2.00 mL of sample solution were diluted to 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 to 5.5.The whole analytical procedure, including all the steps of the sample preparation, was applied in thedetermination of specificity, linearity, range, accuracy and precision. Spiking experiments for recovery andlinearity investigations were performed 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 performed by comparing averageresults of the response of reagents and placebo through a statistical t-test. Linearity was established in therange 4.0 to 12.0 mg L -1 by an F-test for residuals homoscedasticity and a lack of fit test.No statistical difference was obtained between the calibration set performed 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 to 101.3% in spiked validation samplesobtained for lowest, medium and highest calibration levels. Repeatability and intermediate precision wereevaluated by applying an analysis of variance that showed no statistical difference between series performedin sextuplicate for medium calibration level in difference days and by different analysts. Relative standarddeviation of the method resulted in 0.96%.CONCLUSIONSAn extended characterization and validation of the proposed method was carried out following internationalguidance obtaining excellent performance results. The procedure is simple, fast and efficient and may beapplied in the routine quality control of toothpastes.# María Mercedes De Zan Tel/FAX: 54 342 4575205; e-mail: mmdezan@fbcb.unl.edu.ar

ACKNOWLEDGMENTSThe authors thank UNL for financial support from “Proyecto CAI+D 2009 Tipo II PI-12-62and Laboratorio LAFORMED S.A. for 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.