The samples are synthetic, and made from pure water, salts and pure standard chemicals. Most target concentrations are calculated
from the gravimetric data of sample preparation. The estimation of the laboratories' performance is based
on the recoveries of these target concentrations and is, therefore, independent of the number of
participants per round.
Reference concentrations of the parameters are chosen with respect to the concentrations observed in
natural ground and surface waters. It is always aimed to copy the relevant inorganic matrix as close
to natural water samples as possible. Therefore, our PT samples are not simple standard solutions,
but are prepared in such a way that they practically do not differ from real water samples.
They can be analyzed exactly like real samples in routine analysis. No further preparation steps are
necessary. Two samples at different concentration levels are distributed to the laboratories
in each laboratory comparison round.
Based on extensive quality assurance measures during the sample production,
we can ensure high accuracy of the target concentrations. In each round the correctness
of the reference values, homogeneity and stability of the PT samples are checked.