Dipotassium hydrogen phosphate

MOL, purity 98%, was obtained from Optimus Drugs Pvt LTD, India. 200 mg per capsule (R&D prepared samples) was used as the pharmaceutical formulation dosage form. American Society for Testing and Materials (ASTM) grade I water was obtained daily from the central laboratory. Potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, o-phosphoric acid, acetic acid, and anhydrous sodium acetate were supplied by Scharlau, Barcelona, Spain. The solvents used, such as acetonitrile, ethanol and methanol, were also supplied by Scharlau, Barcelona, Spain.
The chosen diluent for standard and test sample preparation was a mixture of ethanol and water in equal proportions.

Potassium permanganate (≥99%) and FOLIN & Ciocalteu's phenol reagent (2 M, with respect to acid) were purchased from Sigma-Aldrich (Darmstadt, Germany). Sodium carbonate anhydrous (reagent grade), potassium hydroxide (extra pure), potassium dihydrogen phosphate (≥99.5%), and dipotassium hydrogen phosphate (≥99.5%) were purchased from Scharlau (Barcelona, Spain). Ethyl acetate (≥99.5%), ethyl methyl ketone (≥99.5%), formic acid (≥98%), ethanol (≥99.5%), methanol (≥99.5%), diphenylboryloxyethylamine, polyethylene glycol, rutoside, chlorogenic acid, and caffeic acid (analytical grade) were purchased from Roth (Karlsruhe, Germany). Distilled water was prepared using a Millipore Q water purification system (Millipore, Billerica, MA, USA). Liquid nitrogen was purchased from Pangas (Dagmersellen, Switzerland), and mushroom tyrosinase (>1,000 Ui) was obtained from Sigma-Aldrich (Darmstadt, Germany).