Andreja Drolc, Milenko Roš
National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia
 

Abstract
The measurement uncertainty of the result of total phosphorus determinations in wastewater was evaluated. Total phosphorus was determined spectrometrically using ammonium molybdate (ISO 6878, 1998). The major sources of uncertainty of the result of measurement were identified as contributions from the linear least squares calibration, repeatability, homogeneity of the sample, storage conditions, and recovery. Identification and evaluation of sources of uncertainty was followed by combined uncertainty calculations. The results show that the major source of uncertainty arose from the calibration curve,  thus leading to the conclusion that calibration is the target operation for reducing the measurement uncertainty of this determination.