Determination of 32 Solvent Residues in Painted Chopsticks by Headspace-Gas Chromatography-Mass Spectrometry and Elimination of Solvent Residues

Small piece of the sample with cross-sectional area of 0.004 m² and length of 30 mm from the food contact part of the painted chopsticks was taken and put into an ampoule. 40 μL of olive oil was added, and the ampoule was filled with nitrogen. After sealing, the above mixture was heated at 80 ℃ for 30 min. The gases released were introduced into the gas chromatograph with a split ratio of 5∶1, and the targets were separated by using DB-624 capillary chromatographic column under the temperature programmed conditions, with carrier gas flow rate of 3.0 mL·min^-1, initial column temperature of 40 ℃ and heating rate of 2 ℃·min^-1. The separated targets were detected by the mass spectrometer with electron impact ion source and selective ion monitoring mode. It was shown that 32 solvents could be completely separated within 28 min, linear ranges of working curves were 0.02-0.20 mg·m^-2 (for m-xylene/p-xylene) and 0.01-0.10 mg·m^-2 (for the other 30 solvents), with detection limits (3S/N) of 0.01 mg·m^-2 (for m-xylene/p-xylene) and 0.005 mg·m^-2 (for the other 30 solvents). Results of test for the spiked recovery was in the range of 80.1%-118%, and RSDs (n=5) of the determined values ranged from 1.2% to 9.7%. The proposed method was applied to the analysis of 20 batches of actual samples, and esters, aldehydes, alcohols, ketones and benzene solvents were all detected. In order to eliminate the effect of solvent residues in samples, the newly purchased samples were pretreated by soaking in different detergents ［1% (volume fraction) detergent solution , 4% (volume fraction) acetic acid solution and 50% (volume fraction, the same below) ethanol solution］ at 40 ℃ for 30 min and by baking at high temperature (25-150 ℃) for 0-120 min, respectively. As found by the results, the solvent residue rates (relative to water) of targets in the sample soaked in 50% ethanol solution were below 100%, lower than those (relative to water) soaked in the other 2 detergents. The solvent residue rates (relative to no baking) in the samples obtained by high temperature baking at 120 ℃ for 80 min were almost 0, and it is suggested that consumers should pretreat the samples with the high temperature baking conditions before using newly purchased painted chopsticks.