Disodium hydrogen phosphate

The reagents sodium carbonate, di-sodium hydrogen phosphate, sodium carbonate, potassium ferricyanide, potassium persulfate, ethylenediamine tetra acetic acid (EDTA) and gallic acid were purchased from Scharlau (Barcelona, Spain). Folin–Ciocalteu’s phenol reagent, absolute ethanol and trichloroacetic acid (TCA) were purchased from Panreac (Castellar del Vallès, Barcelona, Spain). 2,2-diphenyl-1-picrylhydrazyl (DPPH•) free radical, Iron (II) Chloride 4-hydrate, 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylacid (Trolox), (L)-Dehydroascorbic acid and malondialdehyde (MDA) were purchased from Sigma Chemical Co. (Steinheim, Germany, and St. Louis, MO, USA). Propylgallate (PG) was purchased from Acrōs Organics (Fair Lawn, NJ, USA). 2-Thiobarbituric acid (TBA) was purchased from Merck KGaA (Darmstadt, Germany). The following standards were used: phenolic acids—hydroxybenzoic acid, vanillic acid, protocatechuic acid; cinnamic acids—chlorogenic acid, 4-coumaric acid; flavanols—catechin; flavonols—kaempferol, quercetin, kaempferol-3-O-rutinoside, kaempferol-3-O-glucoside, isorhamnetin-3-O-rutinoside, rutin or quercetin-3-O-rutinoside; flavanones—naringenin, eriodictyol, eriodictyol-7-O-glucoside (Merck KGaA, Darmstadt, Germany).

Methyl Prednisolone reference standard (MP), Methyl Prednisolone hemisuccinate reference standard (MPHS), and Methylprednisolone sodium succinate working standard (MPSS) was supplied by UP pharma (Assuit, Egypt). Acetonitrile HPLC-grade, disodium hydrogen phosphate, sodium dihydrogen phosphate, glacial acetic acid 99%, hydrochloric acid 37%, sodium hydroxide, and Hydrogen peroxide 30% (Scharlau, Spain). Water for injection (WFI) was used in the analysis and passed through a 0.45 μm nylon membrane filter before use. Phosphate solution (1) was prepared by weighing 1.6 g of disodium hydrogen phosphate in 1000 mL of WFI. Phosphate solution (2) was prepared by weighing about 0.3 g of sodium dihydrogen phosphate in 1000 mL of WFI.

Guar gum (Mw: 110 kDa) extra pure food grade was attained from Dabur India Limited. Poly (ethylene glycol) (Mw: 400), potassium dihydrogen phosphate (Mw: 141.96 g mol⁻¹), GLYMOL (Mw: 236.34 g mol⁻¹, 98%), acetic acid (Mw: 60.5 g mol⁻¹, 99.8%,) GO powder (product no. 746034, Mw: 4239.48 g mol⁻¹) and H₃BO₃ (Mw: 61.83 g mol⁻¹) were acquired from Sigma Aldrich. Hydrochloric acid (Mw: 36.46, AnalaR) and sodium hydroxide (Mw: 40 g mol⁻¹, Daejung) were used to prepare non-buffer solutions. In addition, disodium hydrogen phosphate (Mw: 177.99 g mol⁻¹, Scharlau), sodium chloride (Mw: 58.5 g mol⁻¹, Merck,), calcium chloride (Mw: 110.98 g mol⁻¹ Merck, anhydrous) and potassium chloride (Mw: 74.55 g mol⁻¹, Daejung) were brought into use for the preparation of phosphate buffer saline (PBS) solution.