## 5 Instrumental Analysis
### Separation Techniques  
As evidenced by the chromatographic conditions reported across the reviewed studies, UHPLC dominates the analysis of non-volatile and semi-volatile NIAS, particularly for polar oligomers, polymer additives, and degradation products. Reversed-phase C18 columns (1.7-1.9 \(\upmu\)m particle size) are the most prevalent, paired with H2O:MeOH or H2O:ACN gradients, usually with 0.1% formic acid or ammonium acetate (5-20 mM) added to enhance ESI efficiency. For instance, [PERSON] et al. [6] employed a C18 column (2.1 \(\times\) 100 mm, 1.7 \(\upmu\)m) with a 10 min gradient (H\({}_{2}\)O:MeOH, 0.1% formic acid) at 0.4 mL/min. Similarly, [PERSON] et al. [23] analyzed extracts from inner polyester coatings using a C18 column (2.1 \(\times\) 100 mm, 1.9 \(\upmu\)m) with a 20 min H\({}_{2}\)O:ACN gradient (10 mM ammonium acetate), demonstrating the method's robustness for the separation of oligoesters. Shorter columns (e.g., 50 mm) and faster gradients (8-15 min) were adopted for high-throughput workflows, as seen in the study by [PERSON] et al. [33], who characterized PA kitchenware migrants using an 8 min gradient (0.3 mL/min). Column chemistry can play a role in resolving specific NIAS classes. For instance, [PERSON] et al. [30] employed a C8 column (2.1 \(\times\) 100 mm, 1.8 \(\upmu\)m) with a 20 min gradient (H\({}_{2}\)O:MeOH, ammonium formate/formic acid), identifying caprolactam, bis(2-methoxyyl) adipate, additives, and cyclic oligomers in multilayer plastic packaging materials for fruit puree and juice by leveraging the column's intermediate hydrophobicity. Similarly, in the work conducted by [PERSON] et al. [56], PP and Tritan(tm) migrants were identified using a phenyl-hexyl column (3.0 \(\times\) 100 mm, 2.7 \(\upmu\)m) with a H\({}_{2}\)O:MeOH gradient, enabling also \(\uppi\)-\(\uppi\) interactions to enhance the separation of aromatic compounds. The integration of ion mobility spectrometry (IMS) with UHPLC-QTOF-MS has increased the identification capabilities for co-eluting NIAS by incorporating collision cross-section (CCS) values as an additional analytical dimension. For instance, [PERSON] et al. [60] conducted IMS to resolve cyclic and linear PLA oligomers, using CCS values to confirm structural assignments. Similarly, [PERSON] et al. [64] employed UHPLC-IMS-QTOF-MS to identify antioxidant degradation products (e.g., Irganox 1010 and Irganox 1076 breakdown compounds) in PE films. In a later study, [PERSON] et al. [66] extended this approach to EVA corks, demonstrating the versatility of IMS in improving identification confidence for structurally similar NIAS across diverse polymer matrices. However, IMS adds complexity to analytical workflows and increases instrument costs, which may limit its widespread  
Figure 2: Common analytical techniques for the NTA of plastic FCMs. adoption. Additionally, the limited availability of comprehensive CCS reference libraries for many NIAS currently constrains confident identification and requires further development to maximize IMS utility in routine NIAS screening. On the other hand, GC remains indispensable for volatile and semi-volatile NIAS. Among different analytical setups, non-polar columns (e.g., DB-5 MS and HP-5 MS) with 5% phenyl-methyl polysiloxane stationary phases (30 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m) and temperature gradients (40-320 \({}^{\circ}\)C at 5-20 \({}^{\circ}\)C/min) are standard [28; 47]. Furthermore, [PERSON] et al. [24] identified aliphatic aldehydes, unsaturated aldehydes, ketones, and hydrocarbons using a CP-Wax 52 CB column (60 m \(\times\) 0.25 mm \(\times\) 0.25 \(\upmu\)m) with a 5 \({}^{\circ}\)C/min ramp to 240 \({}^{\circ}\)C, achieving the separation of structurally similar volatile compounds. Two-dimensional GC (GC \(\times\) GC) also emerged as a useful strategy for complex mixtures, where conventional GC is not able to resolve co-eluting peaks. [PERSON] et al.