Abstract: Isopropylthioxanthone (ITX) has been widely used as the photoinitiator in printing ink of packaging materials in modern food packaging industry. A method regarding the identification and qualification of ITX residue in milk migrated from food contact packaging materials was developed. The procedure was based on the gas chromatography-mass spectrometry (GC-MS) for screening and gas chromatography-tandem mass spectrometry (GC-MS/MS) for confirmation after a solid phase extraction (SPE) step using Florisil column with anthracene D10 (AD10) as the internal standard. Data was acquired in selective ion monitoring (SIM) mode with the following ions: m/z 184,m/z 224, m/z 239, m/z 254 for ITX and m/z 80, m/z 94, m/z 188, m/z 160 for AD10 in screening method of GC-MS. The m/z 254 was selected as the parent ion and m/z 239 as the daughter ion in the conformation method of GC-MS/MS. Data acquired employed the transition of m/z 254, m/z 239 for ITX and m/z 188, m/z 160 for AD10. The method gave limits of quantification (LOQ) of 7.0 μg/L(GC-MS) and 5.0 μg/L (GC-MS/MS) respectively as well as recoveries ranged from 74.9% to 89.6%. The analysis of real samples found two positives out of 11 different milk stuffs available using this method.

Key words: isopropylthioxanthone, mass spectrometry (MS), packaging material , photoinitiator, gas chromatography (GC)