# Commission Regulation (EC) No 401/2006 of 23 February 2006 laying down the methods of sampling and analysis for the official control of the levels of mycotoxins in foodstuffs (Text with EEA relevance), Division 4.3.2.4: Determination of cut-off level and rate of false suspected results of blank samples

Extent: E+W+S+N.I.

The (relative) responses for the negative control and positive control samples are taken as basis for the calculation of the required parameters.
Screening methods with a response proportional with the mycotoxin concentration
For screening methods with a response proportional with the mycotoxin concentration the following applies:
Cut-off = R STC – t-value 0,05 * SD STC
R STC = mean response of the positive control samples (at STC)
t-value: one tailed t-value for a rate of false negative results of 5 % (see table B)
SD STC = standard deviation
Screening methods with a response inversely proportional with the mycotoxin concentration
Similarly, for screening methods with a response inversely proportional with the mycotoxin concentration, the cut-off is determined as:
Cut-off = R STC + t-value 0,05 * SD STC
By using this specific t-value for establishing the cut-off value, the rate of false negative results is by default set at 5 %.
Fitness for purpose assessment
Results from the negative control samples are used to estimate the corresponding rate of false suspect results. The t-value is calculated corresponding to the event that a result of a negative control sample is above the cut off value, thus erroneously classified as suspect.
t-value (cut off – mean blank )/SD blank
for screening methods with a response proportional with the mycotoxin concentration
or
t-value ( mean blank – cut off)/SD blank
for screening methods with a response inversely proportional with the mycotoxin concentration
From the obtained t-value, based on the degrees of freedom calculated from the number of experiments, the probability of false suspect samples for a one tailed distribution can either be calculated (e.g.. spread sheet function ‘ TDIST ’ ) or taken from a table for t-distribution.
The corresponding value of the one tailed t-distribution specifies the rate of false suspect results.
This concept is described in detail with an example in Analytical and Bioanalytical Chemistry DOI 10.1007/s00216 -013-6922-1.

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Source: https://www.legislation.gov.uk/eur/2006/401/annex/II/division/4/division/4.3/division/4.3.2/division/4.3.2.4 (the official version)
Page: https://openlegislation.uk/eu-regulation-2006-401/annex-II/division-4/division-4.3/division-4.3.2/division-4.3.2.4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.