## 6 Data Processing and Analysis
### Identification Confidence and Confirmation  
Confidence in NIAS identification can be systematically categorized using the framework introduced by [PERSON] et al. [80], which ranks confidence from Level 1 (confirmed structure with a reference standard) to Level 5 (exact mass). The described confidence levels and their identification criteria are summarized in Figure 5. This tiered approach underscores the need for transparent reporting, as most NIAS identifications fall into Levels 2-4 due to unavailable analytical standards and limited spectral data in libraries and databases. However, communication regarding identification confidence remains inconsistent across studies, highlighting the need for harmonized reporting standards in NTA. The confirmation and quantification of NIAS in plastic FCMs depend on the availability of analytical standards, which are essential for achieving high confidence in identification (Level 1) and accurate quantification. For instance, [PERSON] et al. [28] confirmed 17 out of >40 compounds (approximately 42%) based on retention time and their respective spectral data with analytical standards, including n-alkanes, toluene disocyanates, BHT, benzophenone, and various phthalate esters [28]. Similarly, [PERSON] et al. [68] confirmed the identity of 12 out of 24 tentatively identified substances (50%) using standards. The remaining detected peaks could not be confirmed due to the lack of commercial standards, and they were considered as tentatively identified. These figures illustrate the practical limitations of full confirmation, with a significant proportion of NIAS remaining at lower confidence levels due to lack of commercially available reference materials. In this sense, the scarcity of analytical standards for many NIAS, particularly oligomers and degradation products, necessitates innovative workarounds. [PERSON] et al. [60] faced this challenge by semi-quantifying PLA oligomers using a cyclic ester oligomer formed by adipic acid (AA), diethylene glycol (DEG), and isophtalic acid (IPA), with AA-DEG-IPA-DEG as the standard. In the work conducted by [PERSON] et al. [64], analytical standards of the proposed compounds were analyzed under the same conditions as the samples to confirm their identity (retention time, CCS values, and fragment matches), including a CCS deviation of \(\leq\)2% as  
Figure 5: Summary of identification confidence levels and identification criteria. Adapted with permission from [PERSON] et al. [80], 2014, American Chemical Society. the confirmation criterion. To enable quantification, calibration curves were constructed using a dilution series of the standards prepared in EtOH. When the standard was not commercially available, the compound was quantified using another standard with a similar molecular structure. This approach, while pragmatic, introduces uncertainties in concentration estimates, especially when the analytes and the compounds used as standards exhibit divergent physicochemical properties. In this regard, quantification challenges are exacerbated by matrix effects, which may alter ionization efficiency and the detector response. For the purpose of correcting matrix effects, [PERSON] et al. [24] quantified volatile NIAS in PET bottled mineral water using standard addition calibration. They employed standards of nonanal, tetradecanal, (E)-oct-2-enal, nonadecane, limonene, toluene, and dibutyl phthalate (DBP). In addition to these substances, nonanal was used to calibrate the quantification of aliphatic aldehydes ranging from C8 to C11, while tetradecanal served for those from C12 to C16. Unsaturated aldehydes and ketones were quantified using the (E)-oct-2-enal calibration curve, whereas nonadecane was applied for the quantification of aliphatic hydrocarbons. In general, the lack of NIAS reference standards is a major bottleneck for their identification, quantification, and risk assessment. Furthermore, the synthesis of custom standards, though ideal, is often cost-prohibitive and time-consuming.