Rapid identification of additives in poly(vinyl chloride) lid gaskets by direct analysis in real time ionisation and single‐quadrupole mass spectrometry

Abstract

Gaskets for lids of glass jars usually consist of poly(vinyl chloride) (PVC) containing plasticisers and additional additives, which may migrate into packed foodstuffs. To conform to legal regulations, any such migration has to be determined analytically, which is a big challenge due to the huge chemical variety of additives in use. Therefore, a rapid screening method by means of direct analysis in real time mass spectrometry (DART-MS), using a single-quadrupole mass spectrometer, was developed. On introducing a plastisol sample into the DART interface, protonated molecules and ammonium adducts were obtained as the typical ionisation products of any additives present, and cleavages of ester bonds as typical fragmentation processes. Generally, additives present in the 1% range could be directly and easily identified if ion suppressive effects deriving from specific molecules did not occur. These effects could be avoided by analysing toluene extracts of plastisol samples, and this also improved the sensitivity. Using this method, it was possible to identify phthalates, fatty acid amides, tributyl O-acetylcitrate, dibutyl sebacate, bis(2-ethylhexyl) adipate, 1,2-diisononyl 1,2-cyclohexanedicarboxylate, and even more complex additives like acetylated mono- and diacylglycerides, epoxidised soybean oil, and polyadipates, with a limit of detection of < or = 1% in PVC plastisols. Only in the case of epoxidised linseed oil were levels of > or = 5% required for identification. The detection of azodicarbonamide, used as a foaming agent within the manufacturing process, was possible in principle, but was not highly reproducible due to the very low concentrations in plastisols.