Effect of instrumental noise in the potentiometric determination of chlorides using as a selective electrode a discarded glass electrode

Abstract

The present study aims to demonstrate the effect of digital voltmeter noise on potentiometric determinations of chlorides, using discarded glass electrodes as selective indicators of chloride ions. A simulation program was developed in Maple 18 that calculates the noise in the measurements of chloride concentrations, considering voltmeters with resolutions of 1, 0.1 and .001 mV. In the program, a deviation of the nominal volume of the volumetric used in the additions of the standards was introduced, in order to simulate the systematic errors of an uncalibrated volumetric. The minimum potential differences that must exist were estimated in order to differentiate two successive concentrations. These values were 19, 2.9 and 1.2 mV, respectively, for the previous voltmeters. The calibration model was simulated for a resolution of 1 mV, voltmeter available in the laboratory, and compared with the experimental model obtained with a discarded glass electrode. The method was applied to the chloride determinations in physiological saline and in a sample of drinking water, using direct calibration and standard addition. The uncertainties were evaluated applying two calculation methods: the propagation of the uncertainties and the simulation of Monte Carlo, which led to recommend the use of a voltmeter with better resolution to obtain results with greater precision.