Agriculture Reference
In-Depth Information
3.1.10
Internal Quality Control
Internal quality control (IQC) measures are used for the ongoing monitoring of
method performance. The method performance quality of each batch of samples
analyzed needs to be checked. The normal methods for this include the use of spiked
recoveries or in-house reference materials and these are analyzed in parallel with the
samples in the batch.
3.1.11 Method Performance Criteria
Method performance criteria are important because they allow laboratories to use any
method of their choice. This is particularly important as many methods require
speci
c instruments and/or software packages that may not be available to the analyst.
This is of no consequence provided that the method meets the minimum required
performance criteria and can be demonstrated to be
with regard to the
various analyte/commodity combinations for which it is to be used. When under-
taking any analysis, it is essential to adopt a robust analytical quality control
(AQC) system in order to be able to demonstrate that the method is under control
and that the results are valid. Such an approach is discussed in more detail in CAC/GL
71-2009 [1].
Initial validation data have to have been generated according to an internationally
recognized standard before any method is put into routine use. If the data are
acceptable to an accreditation body, then the laboratory will become accredited
for that method. If the scope of the method is to be extended, further validation data
will need to be generated for the additional target analytes and/or commodities that are
to be analyzed.
In addition to undertaking routine recovery experiments, preferably with each
batch of sample, it is recommended that laboratories include
“
“fit for purpose
”
check samples
(samples that have been analyzed previously and for which the analyte concentrations
are known). In addition to these
“
blind
”
“
within-laboratory
”
checks,
“
between-laboratory
”
performance checks should also be undertaken. Participation in appropriate profi-
-
ciency tests (PTs) or sending a few samples to another competent laboratory for
analysis is highly recommended.
3.2 QUALITATIVE SCREENING METHODS
Qualitative or semiquantitative screening methods are most likely to be used where
high throughput of samples is needed. Such methods have been developed by analysts
for a wide range of chemical contaminants in food but are most commonly used to test
for veterinary drug residues and, in more recent years, for pesticide residues. Residue
analysts have developed their own class of analyte-speci
c method validation and
AQC guidelines. At the same time, they have also created different terminologies to
describe the important criteria that describe the various aspects of method perform-
ance. Therefore, it is neither helpful nor practical to attempt to produce a generic
