Determination of wine compounds

Sodium metabisulfite 99% (Na₂S₂O₅), tartaric acid (99%), glycerol (99.5%), 1,2-propanediol (99.5%), sodium hydroxide (98%), ortho phosphoric acid (85%), hydrogen peroxide 3% stabilized w/v VINIKIT, indicator 4,4, mixed (methyl red-methylene blue) VINIKIT, sodium hydroxide 0.01 mol/L VINIKIT were from Panreac (Barcelona, Spain). Dichloromethane, ethanol and methanol for gas chromatography analyses were purchased from Merk (Darmstadt, Germany). Glyoxal 40% in water were supplied by Sigma–Aldrich (Madrid, Spain). Water was purified in a Milli-Q system from Millipore (Bedford, Germany). Chemical standards were supplied by Sigma-Aldrich, Fluka (Madrid, Spain), ChemService (West Chester, PA, USA) and Firmenich (Switzerland). Their purity is over 90% in all cases, and most of them are over 99%. Specific details can be obtained from method references [10 (link),22 (link),24 (link)].