QUALITATIVE LIQUID-CHROMATOGRAPHIC ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION MASS-SPECTROMETRIC ANALYSIS OF POLYETHYLENE TEREPHTHALATE OLIGOMERS

The oligomeric fraction of polyethylene terephthalate (PET) has been s tudied as it has the potential to migrate to foods and beverages packa ged in virgin and recovered PET plastics. We have applied positive ion atmospheric pressure chemical ionisation (APCI) to extracts of food-g rade PET resin and beverage bottles. A reversed-phase HPLC system was connected directly to a VG Platform mass spectrometer. An acetonitrile -water-acetic acid gradient elution was performed. Low APCI probe temp eratures (as appropriate for a polyethylene glycol calibrant) produced no significant ions from a PET cyclic trimer standard. A high probe t emperature of 500-600 degrees C gave a strong protonated molecular ion . Characteristic spectra of the cyclic oligomers from the trimer to th e heptamer were obtained. A second homologous series of substances 44 mass units higher than each PET oligomer eluted prior to each PET olig omer. The mass spectra indicated these to be oligomers with one monoet hylene glycol unit replaced by a diethylene glycol unit. To our knowle dge this is the first time that cyclic oligomers above the tetramer ha ve been confirmed by LC-MS. The technique was considerably more sensit ive than published thermospray methods and gave good spectra with sub- microgram quantities injected. This work demonstrates the advantages o f APCI over thermospray as an MS technique for substances of this type .