气相色谱法测定塑料食品包装材料在橄榄油中的总迁移量

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

选择聚丙烯(PP)、聚氯乙烯(PVC)及聚乙烯(PE)材质的食品包装材料作为样品,在作为食品模拟物的橄榄油中浸泡一定时间,令样品中的化学物质向食品迁移。样品在橄榄油中浸泡前后均须在干燥器中放置24h,取出后立即称量其质量m1(浸泡前)及m2(浸泡后)。用正戊烷作为提取溶剂,用自动索氏提取仪提取吸附在样品上的橄榄油,经皂化-甲酯化获得其甲基酯化产物,用气相色谱内标法测得所有生成的酯化产物的峰面积及其加和总面积。并计算此总峰面积与内标峰面积的比值,从标准曲线上查得其相当于吸附在样品上的橄榄油的质量m4。由于所测定3种塑料的挥发性损失质量均<2.0mg,不需作质量校正,因而根据[m1-(m2-m4)]的值以及样品与食品接触部位的表面积(dm^2),即可算出样品在橄榄油中的总迁移量M,mg·dm^-2。应用此方法检测了几十批样品,除PVC旋开盖外,其他样品的总迁移量均低于规定限量。但由于PVC旋开盖的提取物酯化产物的色谱峰与橄榄油酯化产物的色谱峰的保留时间相同,有严重干扰,故橄榄油不适宜于检测PVC旋开盖。

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 of[m1-(m2-m4)]and surface area of the sample in contact with the simulated foodstuff(dm^2).The proposed method has been used for determination of overall migration in tens of samples,all the results of Mfound 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.