Vanb 1

Acetone-d₆, [¹³C₂]ethanol and [¹³C₂]acetic acid (both materials containing 0.99 mol/mol enrichment of ¹³C), and dimethyl sulfoxide-d₆ were obtained from Cambridge Isotope Laboratories (Andover, MA, USA). Chromium acetylacetonate (Cr(Acac)₃, 99%) and HPLC/Spectro grade acetone were obtained from Sigma-Aldrich (Oakville, ON, Canada). IRMS reference materials, IAEA‐CH‐6, USGS65, IAEA-600, NBS22, USGS61, IAEA-603, IAEA-610, IAEA-611, and IAEA-612 were obtained from the International Atomic Energy Agency.
NMR tubes (5 mm inner diameter) were obtained from Wilmad LabGlass (Buena, NJ, USA). Two high-purity synthetic vanillin materials were obtained from NRC [24 (link)]. Maleic acid (SRM grade, TraceCERT®, having a purity of 0.9989 ± 0.0031 g/g) was obtained from Fluka. VANA-1 and VANB-1 are both synthetic high-purity vanillin materials obtained from Fisher Scientific, Waltham, MA, USA) and from Sigma-Aldrich (St. Louis, MO, USA), respectively.

Acetone-d₆ was
purchased from Cambridge Isotope Laboratories (Andover, MA, USA).
Chromium acetylacetonate Cr(Acac)₃, 99% and HPLC/Spectro
grade acetone were obtained from Sigma-Aldrich (Oakville, ON, Canada).
IRMS reference materials IAEA-CH-6, USGS65, IAEA-600, NBS22, USGS61,
IAEA-603, IAEA-610, IAEA-611, and IAEA-612 were obtained from the
International Atomic Energy Agency. NMR tubes (5 mm diameter) were
obtained from Wilmad LabGlass (Buena, New Jersey, USA). Five vanillin
materials, VANA-1, VANB-1 (NMR analysis in previous study^{4 (link)}), VAN-1, VAN-4, and VAN-8 (NMR analysis in this
study; GC-IRMS of all five vanillin samples in this study), are all
synthetic materials of high chemical purity (≥99%) obtained
from Fisher Scientific (Waltham, MA, USA), Sigma-Aldrich (St. Louis,
MO, USA), Alfa Aesar (product of USA), and Sigma-Aldrich (product
of China), respectively.