3 methylphenol

Thirty-six different soybean samples (17 from Korea, 13 from China, and 6 from North America) cultivated in 2016 (Figures S1–S3, Table 4) were used. Soybeans from Korea were provided by the National Agricultural Products Quality Management Service, whereas those from China were obtained from Chinese markets (Figures S4 and S5, Table S4). Soybeans from North America were gifts from a soybean processing company in Korea (Figure S6, Table S4). All samples were stored at −70 °C in a deep freezer before they were analyzed. Solid-phase microextraction (SPME) fibers and holders were purchased from Supelco (Bellefonte, PA, USA), whereas vials and screw caps (Ultraclean 18 mm) were purchased from Agilent Technologies (Santa Clara, CA, USA). l-Borneol was purchased from Sigma-Aldrich (St. Louis, MO, USA). Authentic standard compounds for positive identification of volatile compounds were purchased as follows: 3-methylphenol and hexan-1-ol were purchased from Supelco (Bellefonte, PA, USA), 1,3-benzothiazole, acetaldehyde, α-terpinene were obtained from Fluka (St. Gallen, Switzerland), and acetonitrile was bought from J.T. Baker (Phillipsburg, NJ, USA), while all of the other authentic standards were purchased from Sigma-Aldrich (St. Louis, MO, USA).

Methanol (HPLC gradient grade, 99.9%), acetonitrile (HPLC gradient grade, 99.8%), and HPLC-grade water were obtained from Sigma-Aldrich^® (St. Louis, MO, USA). To determine the solvents, dyes, and CV degradation products, a methanolic solution of 3-methylphenol (99.9%, Supelco^®) was prepared as an internal standard (IS) at a concentration of 1000 µg·mL⁻¹.
Analytical standards used for the calibration of all measured solvents were obtained from Sigma-Aldrich^® and Dr. Ehrenstorfer Laboratories^® (see Table 2).
However, for some compounds, such as Tri-PRS, Di-PRS, and PRS, there were no available standards for calibration. In these cases, the retention time was determined experimentally using ink samples, and the concentrations were analyzed using the Tetra-PRS standard as a reference value.

A mixture of C₇–C₃₀ normal alkanes in n-hexane (HPLC grade) was purchased from Beijing Huawei Ruike Chemical Co., Ltd. (Beijing, China); 6-undecanone (AR) was obtained from Tokyo Huacheng Industrial Pearl Club; sec-butylisothiocyanate-(96%), allyl isothiocyanate (95%), 3-(methylthio)propyl isothiocyanate(98%), benzyl isothiocyanate(97%), phenylethyl isothiocyanate(96%), allyl mercaptan(97%), diallyl sulfide(95%), diallyl disulphide(98%), carbon disulfide(97%), allyl chloride(96%), hexanoic acid(95%), 3-methylphenol(98%), and propylene glycol (99%) were purchased from Sigma-Aldrich Chemical Co. (Saint Louis, USA). Sudan Ⅲ and liquid paraffin were obtained from Beijing Chemical Reagent Co., Ltd. (Beijing, China).