GC-Determination of Overall Migration of Plastic Materials for Food Packaging into Olive Oil

Three kinds of plastics, i.e., polypropene (PP), polyvinylchloride (PVC) and polyethylene (PE), commonly used in making food-packaging utensils, were chosen as samples and olive oil was taken as simulant for foodstuffs. The sample was soaked in olive oil for a definite time, during which the chemical substances of the plastic material might have migrated into the simulant. Before and after soaking of the sample in olive oil, the sample was kept in a desiccator for 24 h, and its mass, m₁ (before soaking) and m₂ (after soaking) was weighed as soon as taking out it from the desiccator. n-Pentane was used as solvent to extract the olive oil adhered on the sample by a automatic soxhlet extractor, and it was determined by GC (with internal standard method) after saponification and methyl-esterification of the adhered olive oil. Values of peak areas of all the methyl esters producted during esterification were taken and sumed up. Ratio of the total peak area to the peak area of internal standard was calculated and the amount of olive oil adhered to the sample (m₄) was found from the standard curve. As the 3 plastic materials concerned, loss of mass due to volatile matter were all less than 2.0 mg, hence correction for loss of mass was not necessary. Then overall migration M (mg·dm^-2) can be found by the formula given based on the data ofm₁-(m₂-m₄) and surface area of the sample in contact with the simulated foodstuff (dm²). The proposed method has been used for determination of overall migration in tens of samples, all the results of M found were below the required limit value, beside the results of samples of PVC screw covers. It was found that the esterification products of extract from PVC material gave chromatographic peak nearly same as those of olive oil, leading to significant positive error. Therefore, olive oil can not be use as simulated foodstuff for PVC screw cover.