The potential of surface-enhanced Raman scattering (SERS) has been investigated for the rapid analysis of two representative organotin compounds (OTCs): dibutyltin maleate (DTM) and tributyltin chloride (TBT), after migration tests from polyvinyl chloride (PVC), as a model food packaging material in aqueous food simulant (acetic acid 3% w/v). OTCs, often used as heat stabilizers additives for PVC, are classified as endocrine disrupting chemicals (EDCs) and their migration potential has to be controlled in compliance with the normative prescriptions for food contact materials. In this study, colloidal silver nanoparticles (AgNPs) were applied as liquid SERS substrate for direct-in-liquid analysis of food simulant after standardized migration tests of PVC samples spiked with OTCs. Promising results were obtained, reaching detection limits below the permitted limits for the considered OTCs (i.e. 0.15 mg/l): DTM and TBT were detected down to 0.01 mg/l and 0.08 mg/l, respectively. Calibration curves were calculated for standard solutions of DTM and TBT in the dynamic range between 0 and 1 mg/l (reduced χ2 = 0.8), and 0.5-5 mg/l (reduced χ2 = 0.2), respectively. Migrated TBT and DTM were detected in the food simulant, specifically identified and quantified by SERS, with a measurement uncertainty around 10% in all cases. In particular, it was found that TBT can migrate in higher amount compared to DTM when the PVC film is in contact with a slightly acidic matrix. These results were further confirmed by inductively coupled plasma-mass spectrometry and UV-Vis spectroscopy. In the present study, direct-in-liquid SERS approach showed to be very promising because it provides a fast response and it allows to overcome most of the common drawbacks of solid SERS substrates due to inhomogeneity problems and low repeatability.
Keywords: Dibutyltin maleate; Food contact materials; Migration test; Organotin compounds; Surface-enhanced Raman scattering; Tributyltin.
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