Round Robin Cuvette Test: Quality Control at an International Level

More than 94 % of all submitted measurement results are correct! This is the excellent outcome of an international round robin test carried out by the independent Dutch institute, Kiwa Water Research, in late 2007. Almost 300 HACH LANGE users in 18 European countries took part. Municipal sewage treatment plants, research laboratories, industrial plants – no matter what the sector, they all performed well. The parameters COD, ammoniumnitrogen, nitrate-nitrogen, total nitrogen, orthophosphate and total phosphate were analysed using LANGE cuvette tests. The analyses were carried out and evaluated in accordance with the Youden methodology.

Organisation and implementation
Kiwa Water Research spiked real wastewater samples with two different concentrations of the parameter to be analysed (COD, TN, NH4-N, NO3-N, Ortho PO4-P and Ptot). The participants therefore determined two diff -
erent concentrations, which differed by a known amount, for each parameter. This concept enables a quick error analysis to be carried out afterwards, e.g. to determine whether deviating results from individual participants
were due to systematic or random errors. The preparedround robin test solutions were preserved and then express mailed to the various countries. The participants had to carry out the analyses within three days of
receiving the samples, then submit the results to the institute no later than 14 days after receiving the samples.

Evaluation and Representation of the Results
After receiving the results, Kiwa Water Research evaluated the data per parameter. As the difference in concentration between the two samples of each Youden pair was known, the accuracy of the values could be checked. The reproducibility of the individual results in the laboratory and/or the repeatability of the results were not tested.