Identification and Quantification of Unknown Antioxidants in Plastic Materials by Ultrasonic Extraction and Ultra-Performance Liquid Chromatography Coupled with Quadrupole Time-of-Flight Mass Spectrometry

Mass spectrometry has been applied to the targeted analysis of commonly used additives (such as Irganox 1010, Irganox 1076, Irgafos 168 etc.) in plastic materials, but a fast and straightforward method for the non-targeted identification and quantification of unusual or potentially new antioxidant additives is still unavailable. In this study, a novel and simple method for the identification and quantification of unknown antioxidant additives in plastic food packaging using ultrasonic extraction and ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry has been developed. A method for the Irganox series analyzed here has not been reported previously. Unknown antioxidant additives have been identified by accurate m/z determination, MS² fragments and comparison with synthesized standards. The mass fragmentation patterns and structural assignments of these antioxidants have been studied. Parameters affecting the efficiency of the process, such as extraction solvents, extraction volume, extraction time and chromatographic conditions, have been studied and optimized. Ultrasonic extraction of plastic materials (40 mg) with dichloromethane (0.5 mL) at 25 °C was applied as optimal. Limits of detection of the target additives ranged from 0.5 ng g⁻¹ to 1.5 ng g⁻¹, and the detection was linear over the range studied (0.01–1.5 μg mg⁻¹, r² > 0.99). The accuracy of the method has been tested by relative recovery experiments with spiked samples, with results ranging from 94.3% to 104.8%, and the precision (relative standard deviation) was within 11.0% (n = 3). Finally, the method has been successfully applied to the determination of antioxidants in several real plastic samples.