Ptfe filters

Dissolution tests were performed using the PTW S III dissolution tester (PharmaTest, Hainburg, Germany). Capsules were tested in a basket apparatus (United States Pharmacopoeia (USP) apparatus I) at 100 rpm and tablets in a paddle apparatus (USP apparatus II) at 50 rpm (unless otherwise stated). A total of 900 mL of dissolution media was used at 37 °C. At predefined times, 5 mL samples were withdrawn. The samples were filtered through 0.45 µm PTFE filters (obtained from Carl Roth GmbH, Karlsruhe, Germany). The sample volume was replaced with blank buffer. Samples were quantified spectrophotometrically (UV–visible spectrophotometer, UV-6300PC, VWR International) at drug-specific wavelengths (diclofenac, 276 nm; mesalamine, 311 nm; paracetamol, 243 nm; and caffeine, 275 nm). During the experiment with bicarbonate buffer, the dissolution media was sparged with a mixture of CO₂ and air to adjust the pH accordingly. The ionic strength of all buffers was adjusted to 154 mM with NaCl. All experiments were performed in triplicate, if not stated otherwise. The time required to achieve 5% release (t_5%) was calculated by linear interpolation and used for comparison. This parameter is most representative of the coat dissolution rather than the whole dissolution profile [16 (link)]. Data are given as mean value ± standard deviation (SD).