Headspace Gas Chromatographic Analysis of Residual Volatile Substances in Polystyrene Food Containers

A headspace gas chromatographic method was developed for the determination of residaul volatile substances (toluene, ethylbenzene, isopropylbenzene, n-propylbenzene and styrene) in food containers made of polystyrene (PS). A PS sample (0.20g) was weighed into a vial and 1.0ml of N, N-dimethylformamide (DMF) as a solvent and 0.5ml of p-diethylbenzene in DMF as an internal standard substance were added. The vial was kept in an oven for 1 hour at 90°C, then 0.5ml of headspace gas was injected into a GC equipped with a capillary column coated with DB-WAX. Calibration of the volatile substances was performed in both external and internal standard modes, and the calibration curves in both cases showed excellent linear correlations between 2ppm to 100ppm for all five substances. The recoveries of the spiked volatile substances from polymer dissolved in DMF were 94-106% in the external standard mode and 90-101% in the internal standard mode.The concentrations of the total volatile substances in PS products determined in the internal standard mode were 217-814ppm, and both ethylbenzene and styrene were observed in all 14 samples. The detection limits were 5ppm for toluene and 10ppm for other volatile substances in the polymer base. Xylene, which is not regulated in the Food Sanitation Law, was detected in 11 samples. These volatile substances, including three isomers of xylene, were confirmed by GC-mass spectrometry.