The determination of polluting species in treated and natural waters is one of the issues most debated today by the world scientific community, an example of these species is the cyanide ion when it exceeds the maximum permissible limits and its rapid quantification is necessary using methods modern analysis, as is the potentiometric method with the use of ion-selective electrodes (ESI). In this work, some characteristic parameters of response of a commercial ion selective electrode (ESI) of half cell, brand ORION USA 9406BN sensitive to cyanide ion, were evaluated. The method used for the determination of the calibration parameters was the method of additions, recommended by the International Commission of Pure and Applied Chemistry (IUPAC), the slope values were found in the range of -61,8 more less 1,23 mv / dec, the practical limit of detection (PLD) and lower limit of linear response (LLLR) in the order of µmol/L; the response time 25 s, was determined by the direct method. The electrode was applied to real samples using 10M NaOH as an ISA solution to adjust the ionic strength and pH of the medium. The sources of typical uncertainties associated to the analysis were evaluated under conditions of repeatability of the method, the uncertainty due to the calibration curve was calculated as the square root of the sum of the squares of standard error of the slope and the intercept respectively. The uncertainty expanded analysis was calculated for 95% confidence.