Institute of Analytical Chemistry, Johannes Kepler University, 4040, Linz, Austria.
Institute of Polymeric Materials and Testing, Johannes Kepler University, 4040, Linz, Austria.
Anal Bioanal Chem. 2021 Feb;413(4):1091-1098. doi: 10.1007/s00216-020-03071-z. Epub 2020 Nov 26.
Recycling will be of increasing importance in the future, especially for plastic packaging waste mainly consisting of polyolefins. One major problem of recyclates comprises impurities which can have a significant negative impact on future product properties. Polyamide 6 can be found widely as contaminant in recycled polyolefins, leading to a need of quantification methods thereof. In this paper, a method development for the quantitative analysis of polyamide 6 is presented based on analysing ε-caprolactam and related cyclic oligomers as marker compounds in model recyclates of high- and low-density polyethylene and polypropylene compounded with low amounts of polyamide 6. For the method development and tentative identification of the different cyclic compounds, a HPLC-QTOF-MS was used and it was possible to detect six different compounds, ε-caprolactam and the corresponding cyclic di- to hexamer. The quantification was performed with a HPLC-QQQ-MS, equipped with a HILIC column, after sample preparation via microwave-assisted extraction. It could be shown that a good linearity from 0.2 up to 5 wt% polyamide 6 in the different polyolefins can be achieved. The cyclic trimer and tetramer show a low limit of quantification and are therefore well-suited for the quantification, whereas the other cyclic compounds can be then used as qualifiers to avoid false positives. To guarantee the applicability of the method, six real recyclate materials were analysed, whereby in three of them low amounts of polyamide 6 could be detected. Graphical abstract.
回收利用在未来将变得越来越重要，特别是对于主要由聚烯烃组成的塑料包装废物。回收料的一个主要问题是杂质，这些杂质会对未来的产品性能产生重大负面影响。聚酰胺 6 作为污染物广泛存在于回收聚烯烃中，因此需要开发定量分析方法。本文提出了一种基于分析ε-己内酰胺和相关环状低聚物作为模型高、低密度聚乙烯和聚丙烯与低量聚酰胺 6 共混物中的标记化合物，对聚酰胺 6 进行定量分析的方法开发。为了开发方法并初步鉴定不同的环状化合物，使用了 HPLC-QTOF-MS，能够检测到六种不同的化合物，即ε-己内酰胺和相应的环状二聚体到六聚体。采用配备 HILIC 柱的 HPLC-QQQ-MS 进行定量分析，样品制备采用微波辅助萃取。结果表明，在不同聚烯烃中，聚酰胺 6 从 0.2 到 5wt%的线性关系良好。环状三聚体和四聚体的定量下限较低，因此非常适合定量分析，而其他环状化合物则可作为定性指标，以避免假阳性。为了保证方法的适用性，分析了六种实际的回收材料，其中三种材料中检测到了低量的聚酰胺 6。
