## 4 Sample Preparation
### Extraction Techniques  
Extraction techniques are essential for isolating NIAS from plastic FCMs or migration solutions, particularly when migration tests alone are not sufficient to mimic the full chemical complexity of polymer components. The reviewed studies employed diverse methods, including solvent extraction, total dissolution-precipitation methods, and solid-phase microextraction (SPME), each with distinct advantages and limitations in terms of efficiency, selectivity, and compatibility with analytical platforms. Solvent extraction remains the most widely used method for extracting NIAS from plastic matrices, using organic solvents to release embedded additives, oligomers, or degradation products. However, solvent selection involves trade-offs between extraction comprehensiveness and selectivity, as well as environmental and analytical considerations. Acetonitrile (ACN) and dichloromethane (DCM) were frequently employed due to their ability to solubilize a broad range of substances from the polymer matrix. While DCM is effective for extracting non-polar compounds, its high volatility and toxicity limit its routine use. ACN offers broader polarity coverage but may be less efficient for extracting hydrophobic NIAS. For instance, PES and PES-PUR coatings in metal food cans were extracted with ACN at 40 \({}^{\circ}\)C for 24 h, obtaining a wide range of additives, oligomers, and oligoesters [23; 44; 45]. Similarly, PP films and candy wrappers were treated with ACN at 70 \({}^{\circ}\)C for 6-24 h, extracting n-alkanes (C21-C29), butylated hydroxytoluene (BHT) and its degradation products, plasticizers (e.g., phthalates), and phenolic compounds, among others [27; 28]. While effective, these approaches may introduce extraction biases that influence the range of detectable NIAS, especially for compounds with extreme polarity or thermal sensitivity. Ultrasonic-assisted extraction, as applied to SAN and ABS kitchenware, enhanced the recovery of styrene and acrylonitrile oligomers, as well as aromatic amines, using methanol (MeOH) at 50 \({}^{\circ}\)C for 30 min [37]. While ultrasonic extraction improves efficiency by facilitating compound release, the use of elevated temperatures and sonication energy may also increase the risk of thermal or mechanical degradation of sensitive NIAS. However, solvent extraction faces some challenges in polymer compatibility. For example, PE and PPusually require more aggressive solvents like DCM or n-hexane:acetone (ACE) mixtures to overcome their crystallinity, whereas polar polymers such as PA and PUR can be readily extracted with EtOH or ACN [31, 46]. On the other hand, total dissolution-precipitation methods are particularly effective for obtaining oligomers and high-molecular-weight NIAS, which are often trapped within polymer networks. These techniques dissolve the polymer, usually in a halogenated solvent (e.g., hexafluoroisopropanol (HFIP) for PET or DCM for PLA), and precipitate it using a non-solvent (e.g., MeOH or EtOH), leaving oligomers and additives in the supernatant. For example, PET pellets and bottles were dissolved in HFIP at 40 \({}^{\circ}\)C for 24 h, followed by precipitation with MeOH at 4 \({}^{\circ}\)C for 1 h [32, 59]. [PERSON] et al. [22] isolated PES oligomers by treatment for approximately 30 min in an ultrasonic bath using a mixture of HFIP and DCM and reprecipitation with 2-propanol. Similarly, PLA-based biopolymers were treated with DCM and precipitated with EtOH [6, 60]. However, these harsh chemical treatments may alter the polymer matrix and potentially affect the stability of certain oligomers or NIAS, which should be taken into consideration when interpreting analytical results. Headspace (HS)-SPME and immersion SPME are solvent-free techniques ideal for volatile and semi-volatile NIAS, minimizing matrix interference. HS-SPME, which absorbs vapors from heated samples, was widely used for analyzing migrants in PET bottles and polyolefin films. The choice of fiber coating plays a key role influencing selectivity.