The interpretation of LC-ESI/MS results is challenging due to the complex interplay between solution chemistry, chromatographic behavior, and ionization processes. Among these, the origin and analytical impact of solvent adducts have not been fully studied, with ongoing discussions on whether such species are formed in solution or during ionization. In this work, the formation, evolution, and analytical consequences of solvent-associated species of an antioxidant (Revonox 501) are investigated using LC-ESI/MS with different ionization modes. This antioxidant is a plastics additive comprising multiple functional groups. The solvent‑associated species and free molecules were separated chromatographically, and the relative abundance of solvent-associated species was shown to increase over time. The investigation of storage time and temperature effects revealed that this solvent-associated species originated from a dynamic equilibrium in solution rather than formed in the gas phase in the MS ion source. Furthermore, mobile phase additives affected the ionization pathway and adduct formation, which in turn strongly influenced the fragmentation behavior in positive ion mode (ESI+). In contrast, negative ion mode (ESI-) showed higher spectral similarity during fragmentation across different species, implying it is a structure-dependent fragmentation. These findings demonstrate that the formation of solvent-associated species is critical in retention behavior, ionization pathways, and fragmentation patterns, highlighting the importance of considering solution-phase equilibria when developing quantitative methods. Here, the excellent consistency of fragmentation in ESI- exhibits potential for LC-ESI/MS analysis of substances similar to AO501.

Hindered amine light stabilizers (HALS) are structurally heterogeneous polymer additives that generate multiple precursor and product ions, complicating their chromatographic separation, structural assignment, and quantitative analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this study, a workflow based on characteristic ions derived from substituted piperidine moieties was developed for the identification and semi-quantification of HALS. Characteristic ions at m/z 140 and 154 were used together with precursor ions, charge state, complementary product ions, and spectral similarity to assign HALS-related components. LC-MS/MS data were acquired in data-dependent acquisition mode (DDA) using the obtained preferred precursor list, and three semi-quantification strategies were evaluated: precursor ion, base-peak product ion, and characteristic ion quantification. Precursor ion and base-peak product ion quantification generally gave comparable apparent recoveries, whereas characteristic ion quantification tended to produce lower values under the applied conditions. Different ion channels showed distinct tendencies, indicating that reliance on a single ion may introduce ion-dependent bias. The use of multiple ion channels and averaging of the resulting concentration estimates reduced the influence of individual ion responses. The workflow enabled the fast identification and semi-quantitative determination of HALS 3346 and HALS 3529 in polymer extracts.

Polyethylene terephthalate (PET) is commonly used in beverage packaging and can be recycled to reduce plastic pollution, raising concerns regarding non-intentionally added substances (NIAS). Here, two organic NIAS, acetaldehyde and benzene, and metal elements have been examined in PET materials. Elemental analysis revealed that higher recycled content in PET correlated with increased contaminant levels. Moreover, elevated acetaldehyde and benzene concentrations were noticed. PET degradation, intentional addition, and unknown sources complicate the analysis of the effects of the production, recycling, and storage on the introduction, formation, or migration of NIAS in PET materials. Benzene and acetaldehyde could migrate into beverages or the environment during storage. The migration of these two volatile substances was therefore quantified. Despite their presence in all PET materials, the low concentrations of acetaldehyde and benzene detected alleviate potential health concerns. This research contributes to the understanding of how recycling and recycled content impact the presence of NIAS in PET, offering insights for optimizing recycling practices and sustaining the role of PET in environmentally responsible beverage packaging.

The cleaning process of recycled polyethylene terephthalate (PET) intended for food contact applications is commonly evaluated using challenge tests. However, the intentional contamination stage of the challenge test may induce morphological changes in PET, which in turn influence surrogate diffusion and retention. In this work, PET pellets with different recycled content and initial crystallinities were subjected to contamination under various temperatures and durations. Differential scanning calorimetry (DSC) was employed to monitor morphological evolution during contamination. Ultrasonic-assisted extraction using ethyl acetate was considered an effective extraction method for residual surrogates, and the concentrations were quantified by liquid chromatography (LC). The DSC results revealed that physical aging occurs at the typical contamination temperature (40°C),while solvent-induced crystallization and structural rearrangement progressively modify the amorphous region in PET with low crystallinity. These morphological changes affect the surrogate diffusion. The LC results showed a non-monotonic contamination profile during prolonged contamination. Contamination levels depend on PET morphology, surrogate physicochemical properties, and contamination conditions. Consequently, differences in crystallinity of PET materials used in challenge tests may influence the apparent contamination level and unintentionally lead to an overestimation of the recycling process. This work systematically demonstrates the interaction of contamination and PET morphology, especially in low crystallinity materials, and highlights the importance of considering morphology-diffusion interactions when interpreting the challenge test results for recycled PET intended for food contact applications.