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- Practical Guide -
Page 89 of 153
The test material is a polymeric material or article which has been synthesized in conformity
with GMP (See also paragraphs 2 and 3 of this report). It contains at least one known
migrateable compound with a relative molecular mass M
r
< 1000. Such a migrant can be an
additive, a residual monomer or an oligomer. Any thickness of the polymeric sample film or
sheet can be used. It is preferable to use a sample with the highest expected thickness for
practical applications.
3.2
Test migrants
It is preferable, if possible, to select a processing additive with well known properties for
which well known and simple chromatographic analysis methods (HPLC or GC) can be used.
A general requirement to the `test migrant' is that it is sufficiently stable under the extraction
and migration conditions. As an example, IRGAFOS 168 was found to be very useful
although being always accompanied by its well-known oxidation product IRGAFOS 168
(ox.). The reproducible mass balance IRGAFOS168/IRGAFOS168(ox). and the analytical
ease of detection allow the simultaneous determination of the sum of parent and degradation
product in this case.
4. Test principle
The test involves principally three steps:
(i)
Extraction of the test material to identify, select and determine quantitatively one or
more suitable test migrants (initial quantity in the plastic, Q).
(ii)
Kinetic migration experiment to measure the diffusion characteristics of the test
material with respect of the time-dependency and extent of release of the test
migrant(s) into a food simulant.
(iii)
Migration/diffusion modelling to establish the basic diffusivity behaviour of the test
sample in terms of an A
p
value.
Depending on the knowledge about the polymeric test sample and its composition, step (i)
and/or steps (ii) and (iii) may be omitted. For instance, in case the polymer is a polyolefin
with well known diffusivity behaviour (defined A
p
value) and if the identity and initial
concentration of the test migrant is known, then calculation of the Q/SM or MIC/SML
relationship according to paragraph 6 (see below) can immediately be applied.
5. Procedure
5.1
Extraction of the test material (step i)
Knowledge of the initial concentration, c
P,0
, of the test migrant(s) in the polymer sample
(homogeneous distribution) is necessary and can be measured following an adequate
extraction procedure with a solvent or swelling agent. The conditions of this extraction
procedure are primarily related to the physico-chemical properties of the test sample and,
once available or established for a given migrant, the procedure can be applied or adapted for
the extraction of any other test migrant.