Identification of unknown compounds from polyester cans coatings that may potentially migrate into food or food simulants

Abstract

Cross-linked polyester resins are being introduced into the market as alternatives to epoxy resins as coatings for metal food cans. Identification of potential migrants, from these coatings into food, is a significant analytical challenge due to the diversity of substances employed in the manufacture of the coatings. However, such identification is required to assess migration from the can coating into the food and quantify dietary exposure. Polyester can coatings were extracted with acetonitrile at 40°C for 24h and the extracts were analyzed by a variety of analytical techniques, including GC–MS, HPLC-DAD/MS, HPLC-DAD/CAD and UHPL C-HRMS. Twenty nine non-volatile oligomers were tentatively identified using retention times, UV spectra, and accurate mass measurements. Identified oligomers suggest the coating in use for food cans is a polyester coating and is mainly based on the monomers isophthalic acid, terephthalic acid and nadic acid. To give confidence in the identification, one of the tentatively identified oligomer was synthetized and analyzed by 13C and 1H NMR and UHPL C-HRMS. The NMR and HRMS results, confirmed the presence of this compound in the can extracts. Finally, to determine if rapid, direct detection of the oligomers was practical, the coatings were analyzed by DART-HRMS. Twenty three out of the 29 oligomers were identified in the coating by direct measurement with DART-HRMS in few minutes.