Summary
The 22nd Norwegian intercomparison study for analysis of freshwater, designated 13-22, was organized in October-November 2013 with 62 participants. It comprised analysis of three sample sets of four samples (A-D, E-H, I-L), and two sample sets of two samples (M-N and O-P), made by adding known amounts of stoichiometric material to water from the river Langli elva in Oslo and the river Kvisla in Aurskog-Høland, which had been filtered through membrane filter with pore size 0,45 µm. The program included 32 parameters: pH, conductivity, turbidity, color, UV-absorption, sodium, potassium, calcium, magnesium, hardness, alkalinity, chloride, sulphate, fluoride, total organic carbon, chemical oxygen demand (CODMn ), phosphate, total phosphorus, ammonium, nitrate, total nitrogen, aluminium, lead, iron, cadmium, copper, chromium, manganese, nickel, zinc, antimony and arsenic. The analysis was largely carried out according to Norwegian standards or equivalent methods. The median of the participants' results, after outliers have been omitted, is selected as the "true" value. The acceptance limit is normally set to ± 20 % of the average true value for the two samples that form a pair. The results are presented graphically in a Youden diagramme, where a circle with the acceptance limit as radius is drawn. The result pairs within the circle are affected by a total error less than the limit and are hence considered acceptable (Appendix A). In total 73 % of participants' results were acceptable, which is somewhat lower than at the previous intercomparisons (Table 1).