In ring tests the same sample is sent to various laboratories who, each in their turn, analyse this sample. It is not known before hand what compounds will be present, nor what concentrations to expect. Each lab then sends its results to the organizer. The results are statistically processed and the overall results are distributed to the participants (together with the appreciation of its own results). The correctness of one’s own result is expressed as a z-score. A z-score between -2 and +2 is considered as good, z-scores between -3 and -2 and +2 or +3 as doubtful, everything else out side this range is considered as bad. Following the accreditation result, it is is expected that a thorough analysis on the possible causes and possibly structural improvement actions are put in place for data which have a z-score outside the -2 and +2 zone.

First  of all there should be a distinction made between reporting limit and LOQ.

An LOQ (LOQ = limit of quantification) is the lowest concentration of a residue that can be identified and quantified. The LOQ is always the result of a validation process and depends on the analytical method used, the characteristics of the analysed product and the kind of crop on which the analysis is done.

Based on the LOQ a reporting border is determined. This is arbitrarily defined, is by definition equal to or higher than the LOQ and, for simplicity, rounded to 10ppb, 20ppb, 50ppb or 100ppb.

For the use of the MSMS technology on residue analysis of pesticides, the reporting limit of 10ppbis usually used because of the legislation requirements. The 10 ppb level (0.01ppm) applies also to baby foods, provided some exceptions.

 ARfD stands for Acute Reference Dose.

The ARfD is defined as "an estimate of the amount a substance in food or drinking water, normally expressed on a bodyweight basis, which can be ingested in a period of 24h or less without appreciable health risks to the consumer on the basis of all known facts at the time of the evaluation"

Why the concept of ARfD?

The assessment of pesticides revealed that one-time consumption of certain crops (one serving) with relatively high residues could lead, in certain cases, to acute problems. In order to be able to correctly assess the health risk, the concept ARfD was set up. This concept was added to the evaluation of effects of contaminants. Previously, evaluation was only done on chronic effects and was mainly focussed on the lengthy and average consumption of contaminants.