background image
- Practical Guide -
Page 91 of 153
In case of very low diffusion and/or thick materials, if necessary, one or two additional time
points are measured between 10 and 20 days to reach or approach equlibrium.
Migration at temperature T2 at worse-case conditions: in dependence of the practical
application a second kinetic migration experiment may be necessary selecting
-
a temperature according to the highest foreseeable contact conditions and
-
3 suitable time points, for instance 0.5, 1.0 and 2.0 times the maximum time test
conditions (97/48/EC, table 3).
Migration measurements are carried out applying duplicate test sample set-up with duplicate
determination of each migration time point and using at least one appropriate food simulant
(fat test using olive oil, if analytically and technically possible) or an alternative/substitute
test medium.
5.3
Diffusion/migration modelling (step iii)
Step 1:
From the kinetic curves measured under 4.2, the diffusion coefficient D
P
and
partition coefficients K
P/F
are derived on the basis of equation (2) of this report.
Step 2:
The wanted basic diffusivity behaviour of the test sample, expressed as A
P
-
value, is derived on the basis of eq. (4) of this report.
Access to the wanted parameters from both steps can be achieved using a suitable computer
programme (step 1) or directly calculated from eq. (4) (step 2), respectively.
6. Establishment of Q/SM or MIC/SML relationship
On the basis of the determined material diffusivity property (A
P
value; Step 2 of 5.3) Q/SM
or MIC/SML relationships can now be established for any other given migrant taking its
molecular weight into account using eq. (3) of this report.
As a worst case, it is recommended to apply the partition coefficient K
P/F
= 1. This is relevant
in the case of high solubility of the migrant in food simulant. In case of low solubility of the
migrant in food simulant a partition coefficient K
P/F
= 1000 was found to be appropriate.