An oligomer is a molecule that consists of a few monomer units. It can be formed during polymer manufacturing and also due to polymer degradation processes or even during use conditions. Since oligomers are not included in chemical databases, their identification is a complex process. In this work, the oligomers present in 20 different PET pellet samples have been determined. Two different sample treatment procedures, solvent extraction and total dissolution, were applied in order to select the most efficient one. The analyses were carried out by UPLC-MS-QTOF. The use of high resolution mass spectrometry allowed the structural elucidation of these compounds and their correct identification. The main oligomers identified were cyclic as well as lineal from the first, second, and third series. All of them were composed of terephthalic acid (TPA), diethylene glycol (DEG), and ethylene glycol (EG). Quantitative values were very different in both procedures. In total dissolution of PET samples, the concentration of oligomers was always, at least, 10 times higher than in solvent extraction; some of the compounds were only detected when total dissolution was used. Results showed that the oligomers with the highest concentration values were dimers and trimers, cyclic, as well as lineal, from the first and second series. The oligomer with the maximum concentration value was TPA₂-EG-DEG that was found in all the samples in a concentration range from 2493 to 19,290 ng/g PET. No differences between virgin and recycled PET were found. Migration experiments were performed in two PET bottles, and results showed the transference of most of these oligomers to a fat food simulant (ethanol 95%).

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低聚物是由几个单体单元组成的分子。它可以在聚合物制造过程中形成，也可以由于聚合物降解过程甚至在使用条件下形成。由于低聚物不包括在化学数据库中，因此其鉴定是一个复杂的过程。在这项工作中，已经确定了20种不同的PET颗粒样品中存在的低聚物。为了选择最有效的一种，采用了两种不同的样品处理程序，即溶剂萃取和总溶解。分析通过UPLC-MS-QTOF进行。高分辨率质谱的使用可以对这些化合物进行结构解析和正确鉴定。从第一，第二和第三系列中鉴定出的主要低聚物是环状的和直链的。它们都是由对苯二甲酸（TPA）组成的，二甘醇（DEG）和乙二醇（EG）。两种方法中的定量值差异很大。在PET样品的总溶解中，低聚物的浓度始终至少比溶剂萃取高10倍；仅当使用完全溶解时才检测到某些化合物。结果表明，最高浓度的低聚物是来自第一系列和第二系列的二聚体和三聚体，环状和直链。最大浓度值的低聚物是TPA 结果表明，最高浓度的低聚物是来自第一系列和第二系列的二聚体和三聚体，环状和直链。最大浓度值的低聚物是TPA 结果表明，最高浓度的低聚物是来自第一系列和第二系列的二聚体和三聚体，环状和直链。最大浓度值的低聚物是TPA在所有样品中发现的₂ -EG-DEG的浓度范围为2493至19,290 ng / g PET。未处理的PET和回收的PET之间未发现差异。在两个PET瓶中进行了迁移实验，结果表明大多数这些低聚物转移到了脂肪食品模拟物中（95％的乙醇）。

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