This paper presents an evaluation of measurement uncertainty regarding the results of anion (nitrate and sulphate) concentrations in wastewater. Anions were determined by ion chromatography (EN ISO 10304-2, 1996). The major sources of uncertainty regarding the measurements’ results were identified as contributions to linear least - square or weighted regression lines, precision, trueness, storage conditions, and sampling. Determination of anions in wastewater is very important for the purification procedure, especially the amount of nitrate in waste and potable waters. The determined expanded uncertainty was 6.1 % for nitrate anions and 8.3 % for sulphate anions. The difference between measurement uncertainties determined by the two methods, the weighted and linear least - square methods, is negligible. <alternatives> [...] </alternatives>
 European Standard EN ISO 10304-2: 1996, Water quality-Determination of dissolved anions by liquid chromatography of ions-Part 2: Determination of bromide, chloride, nitrate, nitrite, orthophosphate and sulphate in waste water (ISO 10304-2: 1995), International Organization for Standardization, Geneve.
 Dionex: DX-100 Ion Chromatograph with SRS Control Operators Manual, 1996.
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