Determination of uncertainty in the measurement of the determination of nitrate with selective electrode to ions

In this work a commercial nitrate selective electrode of the brand ORION, USA 9700BNWP was evaluated. The method used for the determination of the calibration parameters was the method of the additions, recommended by the IUPAC. The slope value obtained was (-60.76 +/- 1.85 mV . dec(-1)), according to what was expected by Nernst for a monovalent anion, the PDL and LLLR were in the order (10(-5) mol.L-1); the response time (20s) was determined by the direct method. The ESI was applied to samples of natural waters, by means of a comparison of paired samples with the spectrophotometric method of UV-Visible analysis, without finding significant differences. The expanded uncertainty of the measurement was estimated under conditions of intermediate precision of the analysis for a 95% confidence with values of 10% for contents lower than 10 mg.L-1 and 6% for higher contents 30 mg.L-1.