2013 ISPAM Mid-Year Mtg Book

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.