Gravimetric Complexometric Titration Method to Determine Mass Fraction of Ethylenediaminetetraacetic Acid Disodium Salt Dihydrate in Candidate-Certified Reference Materials

Abstract

Titrations are a group of techniques that have contributed considerably to developing the chemical industry and chemistry itself. Currently, the Consultative Committee for Amount of Substance has recognized titration as one of the primary methods for determining the amount of substance. In this context, an accurate gravimetric complexometric titration method was implemented to determine the purity of ethylenediaminetetraacetic acid (EDTA) disodium salt dihydrate using a lead nitrate-certified reference material (CRM). The titration reaction was followed potentiometrically using a lead ion-selective electrode. The equivalence point was found by the inflection of a non-parametric regression line that fits the experimental data. The titrations were made in diluted ammonium hydroxide media and sodium tartrate was added to avoid the lead hydroxide precipitation that occurs at high pH. The effect of both concentrations, ammonium hydroxide and sodium tartrate, were evaluated by a Box-Behnken experimental design. A complete uncertainty statement for the measurement method is presented in terms of the International System of Units (SI). The combined relative standard uncertainty of the measurement results is 0.034 % for the purity of the EDTA disodium salt. The atomic weight of the lead that applies to the lead nitrate CRM was determined with mass spectrometry to decrease the uncertainty budget contribution of this parameter which, otherwise, would have been the most important. The main sources of uncertainty were the mass of the EDTA solution for titration blanks, the purity of the lead nitrate CRM, and the precision of the equivalence point determination. The method was evaluated using an EDTA disodium salt dihydrate CRM and no significant bias was found. Finally, the results indicated that the developed method could be used for the value assignment of the mass fraction of EDTA disodium salt dihydrate to produce CRMs.