## 1 Introduction  
Nuclear clarifying agents (NCAs) are a class of additives that have become widely used in the production of several polymers due to their potential to increase optical clarity, physical properties, and resistance to UV radiation, among others. Although important in the production of plastics in several fields of application (e.g., cosmetics and pharmaceutical), but also in food contact materials, these enhanced physical properties are also highly desired in the production of food contact materials (FCMs). That is the case of polypropylene (PP) packaging, in which production NCAs are used to transform that polymer into a more visually attractive alternative than other plastic FCMs like polystyrene (PS) and poly(ethylene terephthalate) (PET) [1, 2]. Many NCAs exist in the market, with most of them having chemical structures based on sugar/sugar polyols, such as sorbitol. The most used ones are marketed under different brand names, including Irgaclear(r), Irgaclear DM(r), and Millad(r). Some NCAs are included in the positive list of additives of the European Commission (EU) Reg. no. 10/2011 for plastic FCMs. That is the case of dibenzylidene sorbitol (DBS, FCM no. 674), bis(methylbenzylidene)sorbitol (FCM no. 752), bis(3,4-dimethylbenzylidene)sorbitol (FCMno. 766) and bis(4-propylbenzylidene)propylsorbitol (PBPS, FCM no. 808). Their chemical structures are shown in Figure 1.  
From this group, FCM no. 674, 752 and 766 have no specific migration limits (SMLs), meaning that they can be used without any individual restriction in the production of food contact plastics. FCM no. 808 is the only NCA with an established SML, 5 mg kg\({}^{-1}\) food [3]. There has been little research to date on sorbitol-based NCAs in FCMs in the literature [2,4]. The lack of commercial analytical standards with known purity is problematic in analyzing FCM additives [5,6]. That is the case of FCM no. 674, a well-known and highly effective NCA commercialized as the first generation product of his class [2,7,8,9,10]. 2,4-bis-O- (benzylidene)sorbitol and 1,3,2,4-bis-O-(p-methylbenzylidene- ne)sorbitol, 1,3:2,4-bis-O-(3,4-dimethylbenzylidene)sorbitol), using both LC-MS and GC-MS. For the latter, a silylation protocol has been applied to ensure the necessary volatility of the analytes for the GC analysis, but no quantitative results were presented. Although used widely in the production of PP, almost no published analytical data regarding its identification in FCMs can be found in the literature. Some exceptions include the work of [PERSON] et al., where it was reported an analytical method for determining NCAs in plastic materials using a GC-MS method after microwave-assisted extraction with in situ silyl derivatization. A derivatization step is necessary to analyze these substances with gas chromatography (GC), as they lack the necessary volatility to use that technique. The authors have also reported a recurrent issue with NCAs, which is their poor solubility in most organic solvents. The issue was solved by using tetrahydrofuran (THF) as an extraction solvent [4]. In another work, [PERSON] et al. reported the identification and analysis of FCM no. 808 migrating from PP beverage cups into food simulant D1 (50% \(v/v\) ethanol/water). Found migration levels were within the established EU regulated levels. Almost no commercial analytical standards for NCAs are available at the moment, hindering the retrieval of information at physical and chemical levels [11]. The only work that has presented consistent information on some NCAs mass spectral data is the one by [PERSON] et al. [2]. However, no analytical method development nor validation and quantification of the analytes were performed. The present study aimed at developing and validating a precise and rapid UHPLC-QTOF-MS method for the analysis of the four NCAs EU regulated as FCM plastic additives.