Determination of Migration of Photointiators in Food Contact Coating

Photointiators have been commercially applied in ultra-violet photocuring ink, varnish, coating, lacquers since 1970s. The significant advantages of efficient, energy-saving and environmental-friendly make them more and more popular in automobile industry, package industry, etc. Photointiators can reach foodstuff by vapour or diffusion from the food contact layer of the package. Although UV ink is just printed in the outer surface of the package, the residue photointiators can transfer to the inner surface by “set-off” effect. Different photointiator has different chemical and physical properties, and shows different response by different testing instrument. In this study, two methods of liquid chromatography time-of-flight mass spectrometry (LC-QTOF MS) and gas chromatography triple quadrupole mass spectrometry (GC-MS/MS) were developed for determination of migration for 23 photoinitiators in food contact coating. The response of the photointiators by two methods was compared for method selection. For the LC-QTOF MS method, an Hypersil GOLD AQ C18 column was utilized and 0.1% formic acid water-methanol was used as mobile phase. QTOF MS was performed by electrospray ion source positive ion mode (ESI⁺) and mutiple reaction monitor high resolution (MRM HR) mode. Simple dilution with acidified methanol was used for migration solution pretreatment and internal standard method was used for quantification. The limits of detection are from 0.0025 to 0.01 mg/kg. Recoveries range from 60.9% to 124%, and the relative standard deviations (RSDs) are between 0.9% and 11.6%. For GC-MS/MS method, a CD-5 column was used, and the MS/MS was operated under MRM mode. Liquid-liquid extraction with n-hexane was used for migration solution pretreatment and internal standard method was also used for quantification. The limits of detection range from 0.0004 to 0.002 mg/kg. The recoveries range from 77.0% to 128%, with RSDs are between 0.4% and 8.1%. Migration solution of 13 batches of metal coating samples were tested, while 5 of them are positive of photoinitiaor TPO or 2,4-diethyl-9H-thioxanthen-9-one, while the maximum detection value of photoinitiaor TPO is 0.0502 mg/kg, the detection values of 2,4-diethyl-9H-thioxanthen-9-one are all less than 0.002 mg/kg. The two methods are easy, sensitive and accuracy, which can determine the migration of photointiators in food contact coating.