Measurement Uncertainty and Compliance in Pesticide Analysis
Regulatory and Technical Reminder :
Regulation N°396/2005 sets the MRLs (Maximum Residue Limits) for each pesticide-crop pair. If the products contain active substances whose levels exceed the MRLs, they cannot be marketed.
For each analytical result, a measurement uncertainty is determined.
The measurement uncertainty is a parameter associated with the result that characterizes the dispersion of the values that could reasonably be attributed to the measurand.
In other words, uncertainty is a confidence interval built around the result in which the “true” value has some probability of being contained.
How do authorities take measurement uncertainty into account in conformity assessment?
The European guide SANTE/12682/2019 “Procedures for analytical quality control and method validation for the analysis of pesticide residues in food and feed” is a document for official control laboratories throughout the European Union.
The guide specifies that the interpretation of results should be carried out using uncertainty in order to verify the compliance of the sample.
In order to cover inter-laboratory variability between different laboratories, it is recommended that national regulatory authorities use a default “increased” measurement uncertainty of 50%.
To use this common uncertainty, each laboratory should demonstrate that its own analytical method achieves a measurement uncertainty of less than 50%.
In E15, the guide states that the result should be reported
as follows:
Result = x ± U (units), where x is the measured value and U is the measurement
uncertainty.
In the context of official food controls by regulatory authorities, compliance
with the MRL should be verified as follows :
The sample is considered non-compliant if x-U> MRL.
As an example :
If MRL = 1mg/kg
Result x = 2.2mg/kg and U = 50%, then (x-U) = (2.2- 1.1) = 1.1 > MRL or
NON-conforming sample.
If MRL = 0.5mg/kg
Result x = 0.8mg/kg and U = 50% then (x-U) = (0.8 – 0.4) = 0.4 < MRL i.e.
CONFORM Sample
Therefore, “downward” uncertainty should be taken into account when concluding on the compliance of a sample.
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