Ring tests

General information about the implementation of ring tests in VDLUFA

In VDLUFA, the specialist groups for soil testing, fertilizer testing, seeds, feed testing, milk and environmental and trace analysis carry out regular ring tests

  • for method validation and evaluation,
  • for external quality assurance 
  • for the certification of reference material.

Participation in these internal ring tests is only available to association members.

The ring tests primarily examine feed and fertilizers, soils, horticultural soils and seeds. This not only ensures a high quality standard is achieved in the participating laboratories, but the methods are also subject to constant review due to the variety of test samples and the different concentrations of the parameters in the respective test samples.

The VDLUFA also offers two public ring tests that are also open to non-members:

  • EU fertilizer ring test
  • Feed ring test.


Methodical ring tests

During method validation, important quality parameters such as repeatability coefficient, comparative variation coefficient, recovery rate and measurement uncertainty are determined. Each test must be carried out with at least 8 different laboratories. All laboratories should have comparable competencies in the analytical field relevant to the method being tested. From the test results, statements can be made about the robustness of a method, the performance of the laboratories and the samples examined in the test. To derive the analysis tolerance, content-range-dependent statistical parameters such as comparative variation coefficient, measurement uncertainty and Horwitz ratio are used in tests.


The evaluation

The VDLUFA carries out ring tests according to the state of the art, generally applicable rules and current standards (e.g. AQS leaflet A3 (9/1998), DIN 38402 A45, International harmonized protocol for the proficiency testing of analytical chemistry laboratories, IUPAC Technical Report (2006), Tattersfield method for seeds). VDLUFA ring tests are evaluated using software authorized by VDLUFA (currently ProLab from quodata (Dresden). Minimum requirements apply in VDLUFA for the documentation and archiving of interlaboratory tests.