Syringe filters

Uniformity of content is an important test to ensure homogeneity in the distribution of the drug and polymer within film preparation. Three strips each of 1 cm² in size were cut and dissolved in 5.7 pH buffer under continuous stirring, using a magnetic stirrer. The solution was filtered using syringe filters (0.22-μm, Sterlitech, Bedford, MA, USA) of nylon material to remove undissolved particles. The prepared mixture was analyzed using a UV-Visible double beam spectrophotometer (Halo DB-20 UV, Progen Scientific, Livingston, UK) at 220 nm wavelength [34 ]. The content uniformity of each formulation was determined in triplicate and finally calculated by using the following Equation (2).
$$\% \mathrm{drug} \mathrm{content}=\frac{\mathrm{Actual} \mathrm{amount}}{\mathrm{Theoretical} \mathrm{amount}}\times 100$$

The Folin–Ciocalteu reagent and phenolic compound standards (chlorogenic acid, gentisic acid, sinapic acid, vanillic acid, gallic acid, p-coumaric acid, caffeic acid, apigenin, naringenin, rifampicin, quercetin, kaempferol) were obtained from Sigma Aldrich (St. Louis, MO, USA). HPLC grade methanol was acquired from Sigma Aldrich (St. Louis, MO, USA). Zinc acetate, sodium bisulfite, and sodium carbonate were purchased from Sigma Aldrich (St. Louis, MO, USA). Potassium ferrocyanide and hydrochloric acid were purchased from Fisher Scientific (Fair Lawn, NJ, USA). Ultrapure water was obtained from a Milli-Q water purification system (Nalgene, Rochester, NY, USA). Solid phase extraction (SPE) Sep-Pak C18 cartridges (500 mg, 3 mL) were purchased from Waters (Milford, MA, USA). Syringe filters (0.45 µm, diameter 25 mm) were acquired from Sterlitech (Auburn, WA, USA).

The o-phenylenediamine reagent and quinoxaline standards were purchased from Sigma Aldrich (St. Louis, MO, USA). HPLC grade methanol was acquired from Sigma Aldrich (St. Louis, MO, USA). Sodium phosphate monobasic and sodium phosphate dibasic were purchased from Sigma Aldrich (St. Louis, MO, USA). 3-deoxyglucosone (3-DG) was purchased from Santa Cruz Biotechnology (Dallas, TX, USA). Pure methylglyoxal, glyoxal standards were procured from Sigma Aldrich (St. Louis, MO, USA).
Sep-Pak C18 cartridges (500 mg, 3 mL) for SPE were purchased from Waters (Milford, MA, USA). Syringe filters (0.45 µm, diameter 25 mm) were acquired from Sterlitech (Auburn, WA, USA). Ultrapure filtered water was obtained from a Milli-Q water purification system (Nalgene, Rochester, NY, USA).