Simultaneous determination of cyclic PET and PBT oligomers migrated from laminated steel cans for food

Abstract

In this paper, three commonly used PET and PBT copolymers films as inner gauge materials of laminated steel were screened and identified, and then 6 kinds of cyclic PET and PBT oligomers that could be obtained as commercially available standards were selected from the screening results for research. An ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) technique for simultaneous detection of cyclic PET and PBT oligomers in laminated steel cans was first developed. Four different laminated steel metal cans were selected to carry out the migration tests at 40 °C for 10 days in three food simulants of 10% ethanol, 50% ethanol and isooctane. Then commercially acquired cyclic PET dimer to pentamer, cyclic PBT dimer and trimer were used as external standards, and the six oligomers in the migration solutions were quantitatively analyzed by UPLC-QTOF-MS technology. The results showed that all oligomers could be separated well with good linear relationship and high limit of detection. The recoveries of cyclic PET and PBT oligomers ranged from 80.00% to 105.18%, which indicated that UPLC-QTOF-MS was an effective method for simultaneous determination of cyclic PET and PBT oligomers in laminated steel cans. Among the six oligomers tested, cyclic PET trimers and cyclic PET tetramers had the most migration. In addition, the total content of the six oligomers for every can was all the largest in isooctane simulant, meanwhile the content of oligomers in 50% ethanol simulant was far greater than that in 10% ethanol simulant. Moreover, the influence on the amount of oligomers migration by comparing the sterilization and non-sterilization process was studied to find that high sterilization temperature produced more migration and the test methods prescribed by the EU and China standard regulations may cause an underestimate of the amount of oligomer migration.