Residue analysis is a field of analytical chemistry which strongly relies on the confidence which can be attributed to measurement results. Consequently, no result in residue analysis ever stands isolated. Every analysis is rather approached as embedded into quality control measures whose purpose is inter alia the control of environmental influences, the demonstration of adequate performance of methods, as well as the provision of clear documentation of all involved processes. It is through these quality control measures that reliability in analytical results can be established.
Apart from internal quality control measures which guarantee the validity of results on a day-to-day basis, it is also necessary to verify method performance against external criteria. One method to accomplish that is through the participation in proficiency tests, which is also a requirement under ISO 17025. In contrast to internal quality control measures, proficiency tests may offer additional information on trueness and bias and they give the participants feedback on their performance in comparison to other laboratories.
The EURL Berlin also values proficiency tests because they may provide information on the performance of different analytical approaches and can be used as a tool for the assessment of measures towards the harmonisation of laboratory performance (e.g. collaborative trials).