Nist08

The identification of volatile metabolites was carried out on the base of their mass spectra and retention index (RI) values. Comparison of the mass spectra was based on the NIST08 and Wiley 9 mass spectral libraries (Agilent Technologies, Palo Alto, CA, USA). The RI values of volatile metabolites were calculated with an alkane mixture from C₇ to C₃₀ as external standards. Volatile metabolites were quantified by comparing their peak areas to that of the internal standard, (1R,2S,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol((+)-borneol) (100 ppm w/v in methanol). The relative peak area (%) was an average of triplicate measurements.
Non-volatile metabolites were identified by comparing retention times and mass spectra with those of authentic reference compounds. GC-TOF/MS raw data were obtained from ChromaTOF™ software (Leco). All non-volatile metabolites were identified using Fiehn library, mainlibrary, Wiley 9 and in-house library. For quantification of non-volatile metabolites, 20 μL threitol (100 ppm w/v in water) for carbohydrates, 10 μL heptadecanoic acid (100 ppm w/v in hexane) for lipids, 10 μL tropic acid (100 ppm w/v in water) for organic acids and 10 μL norleucine (100 ppm w/v in water) for amino acids were used as internal standards.

A micro-furnace Py–GC–MS (7890A/5975 Inert, Agilent Technologies, Santa Clara, CA, USA) (Figure 2) was used to determine the presence of PVAc in chewing gum. A PVAc reference standard (RS) and commercial chewing gum (CG) were used as the standard polymer and actual sample, respectively.
For the Py–GC–MS analysis, 0.3 ± 0.05 mg of the RS or CG was placed in a deactivated metal cup and inserted into the pyrolyzer furnace, which was preheated to 400 °C. The pyrolysis product vapor emitted from the furnace was transferred to a metal capillary column (UA-5, 30 m × 0.25 mm i.d. × 0.25 µm film thickness) via a split/splitless inlet (320 °C, split ratio 200:1) and cryofocused at the front of the column using liquid nitrogen (−195 °C) for 3 min. After cryofocusing, the pyrolysis products were separated on the column under non-isothermal GC oven heating, detected using a quadrupole MS, and identified by comparing the mass spectra with those in the NIST 08 (Agilent Technologies, Santa Clara, CA, USA) and F-Search (Frontier Laboratories, Koriyama, Japan) libraries. The Py–GC–MS operation conditions applied in this study are given in Table S1.