The sample shall be divided into two sub-samples (sub-sample 1, sub-sample 2). Inoculation
is done directly into the sub-samples.
The inoculated sub-samples shall be stored for x to allow the microorganisms to equilibrate
with the matrix.
After equilibration, each sample is diluted 1/10 in an appropriate diluent.
One sub-sample shall be performed in duplicate by operator 1; the second sub-sample is
tested by operator 2 only once.
The inoculation procedure is described in Annex B (
to develop
).
8.4 Determination of trueness
For microbiological methods it is not possible in practice to determine a true value. In
primary validation, inter-laboratory studies are used for estimation of a “true” value.
Trueness in a user laboratory can be estimated by:
- participation in interlaboratory comparisons such as proficiency testing and plotting z-scores
to show any trends;
- use of microbiological RM or CRM;
- recovery experiments with spiked samples using a non-selective method to establish a
reference value.
NOTE:
re
covery experiments should only be used if proficiency tests or CRM are not
available.
1...,71,72,73,74,75,76,77,78,79,80 82,83,84,85,86,87,88,89,90,91,...178