A headspace gas chromatographic method was developed for the determination of residal volatile substances (toluene, ethylbenzene, isopropylbenzene, n-propylbenzene and styrene) in food containers made of polystyrene (PS). A PS sample (0. 20 g) was weighed into a vial and 1. 0 ml of N, N-dimethylformamide (DMF) as a solvent and 0. 5 ml of p-diethylbenzene in DMF as an internal standard substance were added. The vial was kept in an oven for 1 hour at 90C, then 0. 5 ml of headspace gas was

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... 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 2 ppm to 100 ppm 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 217814 ppm, and both ethylbenzene and styrene were observed in all 14 samples. The detection limits were 5 ppm for toluene and 10 ppm 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.