Migration of cyclic dimethyl siloxanes from silicone elastomers into food – determination of D4 to D25 via on-line coupled HPLC-GC-FID

A robust method for the analysis of cyclic siloxanes D4 to D25 <i>via</i> on-line coupled HPLC-GC-FID is presented to provide reliable data for the migration of these oligomers, in particular, into fatty foods. Post-cured and non-post-cured platinum silicone moulds were tested under different conditions of repeated use (baking at 180 °C, 15 min; chocolate preparation at max. 45 °C, 2 h). Overall siloxane migration analysis <i>via</i> ¹H-NMR as well as oligomer profiling in the materials <i>via</i> GC-FID were performed to obtain a comprehensive picture. Maximum transfer was determined into shortcrust pastry for D7 (29.9 mg/kg food, 1^st cycle), which was 6.4% of its initial content in the non-post-cured material. Noteworthily, under hot-use conditions, volatile siloxanes from non-post-cured materials were released mainly into ambient air, and less into food (e.g. during five cycles of baking, approx. 1% of the initial D5 amount migrated, but approx. 98% were evaporated). Post-curing sufficiently reduces migration of siloxanes < 1000 Dalton (e.g. sum D4 to D13, shortcrust pastry, 153 mg/kg from non-post-cured and 9.5 mg/kg from post-cured mould, 1^st cycle). However, migration of oligomers > D20 is almost independent of post-curing and can cause an issue in terms of the overall migration limit of 60 mg/kg (e.g. 167 mg/kg total siloxanes migrated into shortcrust pastry, 3^rd cycle). Also, at moderate temperatures during chocolate preparation, significant migration was determined (e.g. 21.5 mg/kg total siloxanes, 3^rd cycle). In terms of risk assessment of multiple use articles made from silicone, the use of food simulant D2 can cause significant underestimations in the 3^rd cycle, because of an almost total extraction during the first two migration cycles. Therefore, the assessment of silicone articles should be based on real food application testing - an appropriate method for this is presented using HPLC-GC-FID.