In a study published on February 22, 2016 in the peer-reviewed journal Food Additives & Contaminants: Part A, Zsolt Bodai and colleagues from the Joint Research and Training Laboratory on Separation Techniques (EKOL), Eötvös Loránd University, Budapest, Hungary, compare solubility to specific migration limits (SMLs) for several compounds. They suggest that migration studies can be waived in cases when solubility is (much) lower than the SML.
Solubility values at 25°C were determined for six UV stabilizers and five antioxidants in 3% acetic acid, 10%, 20% and 50% ethanol, sunflower oil, and two common beverages, cola and fruit juice. Solubility measurements were based on the OECD guideline Test No. 105 for determination of water solubility, modified by the authors in order to reduce the performance time. In particular, 3 x 25-min ultrasonication treatment was used instead of 3 days of stirring as suggested in the original guideline, and the equilibration period was reduced to 2 hours instead of 1 day. The performance of both methods, original and modified, was judged to be similar. However, it has to be noted that direct comparison was carried out only for one compound (Tinuvin 327, CAS 3864-99-1) in one food simulant (50% ethanol).
The limit of detection (LOD) and limit of quantitation (LOQ) of the analytical method for the 11 tested compounds were 0.5-5 µg/L and 1-10 µg/L, respectively. The solubility of all tested compounds, except Tinuvin P (CAS 2440-22-4), turned out to be below the LOD in 3% acetic acid, 10% and 20% ethanol, and both beverages. Thus, it could be demonstrated that in all these polar matrices the solubility is below the SMLs (0.05 – 60 mg/kg) for all compounds tested (including Tinuvin P). In 50% ethanol, 7 out of the 11 compounds could be measured, with the SML exceeded for two of them (Irganox 3790, CAS 40601-76-1, and Tinuvin P). In contrast, in sunflower oil the solubility of all compounds exceeded 1 g/L, a value at least one order of magnitude higher than most SMLs.
The authors argue that if the solubility of a certain compound under conditions similar to those used in migration studies is known to be ‘significantly’ lower than the SML for this compound, the migration assessment can be omitted. In this way, determining solubility prior to migration studies could allow for faster and cheaper testing of food contact materials. However, it is noteworthy that legal compliance for migrating compounds always applies to actual food, not food simulants.
Bodai, Z., et al. (2016). “Solubility determination as an alternative to migration measurements.” Food Additives & Contaminants: Part A 33:574-581.