blank materials spiked after sample preparation and prior to anal-
ysis (Table 2). These experiments aimed at comparing whether a
blank cheese powder spiked directly before analysis behaves the
same way in terms of recovery as a candidate RM (cheese, homog-
enised to a slurry, spiked, converted into cheese powder). The
results obtained provide an indication of the absence of adverse
material changes due to processing.
Procedure III is most suited for producing large batches of con-
taminated cheese powder: only a small amount of highly contam-
inated material needs to be processed, which is then step-wise
diluted with blank material to the desired target level. The vast
majority of cheese can be freeze-dried as such and does not need
to be converted into a cheese slurry before freeze-drying (difficul-
ties to handle and homogenise dozens to few hundreds of kilos of
cheese soup). It was therefore decided to apply procedure III for
processing the candidate RM batches.