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Waste water PTs

"Länderübergreifende" proficiency tests (LÜRV; inter-state proficiency tests)

The German Working Group on water issues of the Federal States and the Federal Government (LAWA) fixed the way of doing PTs in the regulated environmental sector in its AQS-leaflet A-3 for the analysis of water, waste water and sludge.
To conduct these PTs in a nationwide uniform and harmonized way, the following PT providers in the different German states cooperate in a planning group under the supervision of the responsible LAWA-subcommittee and provide the PTs together (all linked websites are in German only):

The planning group defines the key points for this PT round and several PT providers organize the round then in an identical way.

PT programme

The PT programme is geared to fulfill the requirements of the "Technical Module Water" (Fachmodul Wasser), where the parameters relevant for the examination of water in the regulated environmental sector are divided in several sub-groups:

  • sub group 1: sampling and general characteristics
  • sub group 2: photometry, ion chromatography, titration
  • sub group 3: element analysis
  • sub group 4: group and sum parameters (part 1)
  • sub group 5: group and sum parameters (part 2)
  • sub group 6: gas chromatographical methods
  • sub group 7: HPLC methods
  • sub group 8: microbiological methods
  • sub group 9: biological methods, biotests

The "Technical Module Water" can be found in the (German) "Recherchesystem Messstellen und Sachverständige" of the LAWA.

The PT programme is fixed by the LAWA subcommittee "leaflets" based on a proposal of the planning group.

Evaluation and assessment

The evaluation and assessment is based on the requirements of DIN 38402 - A45 and the LAWA-AQS-leaflet A-3 ("Requirement for external quality check of laboratories").
The assigned value is defined on the basis of the robust mean of the results of all participants. The standard deviation necessary for the calculation of the zU-scores also is derived from the results of the participating laboratories. The planning group decides upon upper and lower limits for the standard deviation prior to the PT round. The intention of these limits is the prevention of too stringent or too slack quality requirements in the PT.
After finishing the PT round all participating laboratories get an evaluation data sheet where all results are marked with "+" or "-" to show the assessment of this value. In addition for each parameter it is documented whether this parameter was analysed "successful" or "not successful". "Successful" means that more then 50% of the results for this parameter were within the tolerance limits. Parameters that were not analysed are marked with "not participated".
If at least 80% of the values that had to be analysed in the PT were positively assessed and at least 80 % of the parameters were assessed as "successful" then the participation in total is assessed as "successful". This is also stated on the evaluation data sheet. All "successful" participants in addition get a certificate stating the successful participation.
Of course all participants also get a comprehensive evaluation report, stating the results of all participating laboratories in an anonymuous way together with many tables and figures.
These reports are also available from the AQS-BW website.