Sodium hydroxide (naoh)

The solutions were prepared with analytical grade chemicals and Milli-Q® Water (resistivity > 18.2 MU cm, Millipore, Bedford, MA, USA).
The permanganate solution was prepared with boiled water by diluting a stock solution of 0.1 M to a nal concentration of 5 mM. A stock solution of 0.1 M permanganate was prepared by dissolving 1.58 g of sodium permanganate in 100 mL of water.
A 1.5 M sodium hydroxide stock solution was prepared, dissolving 30 g of sodium hydroxide (PanReac, Spain) in 500 mL of water.
A HYP stock solution of 1000 mg L -1 was prepared by dissolving 10.0 mg of L-hydroxyproline (Sigma Aldrich, Germany) in 10.0 mL of water. The working standards within a range of 25.0 mg L -1 to 500 mg L -1 were prepared from the stock solution.

Conventional white table wine was used. NaOH (sodium hydroxide) was purchased from @PanReac AppliChem and it was used to prepare two different concentrations of NaOH solution (1 M and 0.1 M). The pH of wine was adjusted to pH 3.52 by adding 3.5 ml NaOH [0.1 M] to 30 ml of wine and 0.35 ml of NaOH [1 M] to 40 ml of wine to achieve pH 3.74. All pH measurements were performed at room temperature-Tª (20 °C).
Tartaric acid (2,3-Dihydroxybutanedioic acid) was purchased from @Merck Schuchardt OHG. Three tartaric acid concentration were prepared (0.1 M, 0.5 M and 1 M).
Methyl orange (Sodium 4-{[4-(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate) was selected as the pH indicator. Methyl orange has a transition range of pH 3.0 up to pH 4.0 (Ethier & Simmons, 2007) (link) being red at pH 3.0 or inferior values and remaining yellow at pH 4.0 or higher. Therefore, it is suitable for the expected pH values in white wines.