Pyruvaldehyde

All the reagents were of the highest commercial purity available, obtained from Sigma-Aldrich^®, St. Louis, MO, USA, and included the following: DL-glyceraldehyde (>90%), acetaldehyde (>99.5%), pyruvaldehyde (40 wt. % in H₂O), glyoxal (40 wt. % in H₂O), glycolaldehyde (>90%), orcinol (>99%), D-glucose (99.9%), D-ribose (99.9%), and FeCl₃ (95%). Methanol-free formaldehyde was prepared from paraformaldehyde according to the method described by [23 (link)]. Acetonitrile (HPLC), ethanol (HPLC), H₂SO₄ (95–97%), HCl (37 wt. % in H₂O), HNO₃ (70%), KOH (>85%), and 2,4-dinitrophenylhydrazine (DNPH) (97%) were obtained from Merck Co.^®, Kenilworth, NJ, USA. Natural iron(III) hydroxide oxide samples were collected in Durango, Mexico, and were characterized by X-ray diffraction, Raman, and X-ray Photoemission spectroscopy (XPS). To eliminate organic contamination, the goethite samples were treated with a 3% HNO₃ solution (acid wash), followed by two additional washes with Milli-Q^® (Merck Millipore, Burlington, MA, USA) water (deionized) and a 3% KOH solution. After the acidic and basic washes, the mineral samples were rinsed with Milli-Q^® water and dried in a desiccator at room temperature for 24 h.