Threose

Except where noted otherwise, deionized water (Nanopure II, Thermo Scientific, Waltham, MA, USA) was used in the preparation of all reagents. The primary analytical standard of CTV was produced by Hayashi Pure Chemical Ind., Ltd. (Osaka, Japan). For spiking of rice samples, a standard material containing both CTV and iso-CTV prepared at the USDA-NCAUR (Peoria, IL, USA) was used [21 (link)]. Acetonitrile and methanol were HPLC grade and were purchased from Fisher Scientific (Hampton, NH, USA), as was polyvinyl alcohol (PVA). 1-1′carbonyldiimidazole (CDI), 4,6-dimethyl-2-oxo-2H-pyran-5-carboxylic acid (IDHA), 4,6-dimethyl-α-pyrone (DMP), and threose were purchased from Sigma-Aldrich (St. Louis, MO, USA). All other chemicals were reagent grade or better and purchased from major suppliers.

The irradiated and melted samples were evaporated under vacuum inside a vial vessel and analyzed for the presence of saccharides. The measurements were performed using a ITQ 1100 GC–Ion Trap MS system (ThermoScientific, USA), equipped with an Xcalibur MS Platform using a non–polar TG–SQC column (ThermoScientific, USA). 17 μL of hexamethyldisilazane (99% HMDS, CAS 999–97–3, Sigma Aldrich), 6 μL of chlorotrimethylsilane (99% TMCS, CAS 75–77–4, Sigma Aldrich), and 52 μL of pyridine (99.5% anhydrous, Scharlau) were added to the residue as derivatization agents and aprotic solvent, respectively. The vial was then heated at 70 °C for two hours. Subsequently, 0.5 μL of the sample was injected into the chromatograph, and the measurements were performed using a column temperature range of 180–280 °C with a temperature gradient of 30 °C min⁻¹. The mass spectrum was compared with the GC chromatograms and MS spectra of D–forms of ribose, lyxose, xylose (99%), arabinose (98%), threose (60% syrup), ribulose (1 M solution) and xylulose and xylose (98% syrup) standards (all from Sigma Aldrich). Liquid–phase standards (i.e. threose, ribulose and xylulose) were evaporated under vacuum in the presence of phosphorus pentoxide prior to GC–MS analysis.