Determination of monomers and oligomers in polyethylene terephthalate trays and bottles for food use by using high performance liquid chromatography-electrospray ionization-mass spectrometry

The types and contents of monomers and oligomers in polyethylene terephthalate (PET) food containers were analyzed using HPLC-ESI-MS after being extracted with 50% acetonitrile or dichloromethane using an accelerated solvent extraction unit. The types of cyclic oligomers were classified into first and second series. The first series represented a type of [TG]n composed of terephthalic acid (TPA; T) and monoethylene glycol (EG; G) at a ratio of 1:1. The second series showed a type of [TG]nG in which a single G unit was substituted by diethylene glycol (DEG; GG). The oligomer level extracted using dichloromethane was measured at 4024-11576 mg kg−1. The first series cyclic oligomers, second series cyclic oligomers and linear oligomers constituted 83.0-90.6%, 7.8-14.7% and 1.3-2.8%, of the total extracted oligomers, respectively. The extracted amounts of TPA, monohydroxyethyl terephthalate and bishydroxyethyl terephthalate using 50% acetonitrile were 3.0-28.2 mg kg−1, 16.8-118.2 mg kg−1 and 3.9-26.7 mg kg−1, respectively. The A2, A3, S2 and S3 groups as modified oligomers were detected as 42.9-221.4 mg kg−1, 17.2-250.3 mg kg−1, 1.1-48.1 mg kg−1 and 1.0-19.8 mg kg−1, respectively. The results of this study demonstrate an advanced analytical approach to determine the residual oligomers and monomers in PET products for food use and imply their potential migration to foodstuffs.