Polysorbate 80 ps80

Four different types of surfactants were used: Benzalkonium chloride (BZC) (Sigma-Aldrich, Tokyo, Japan) as a cationic surfactant, sodium dodecyl sulfate (SDS) (Sigma-Aldrich) as an anionic surfactant, 3-(3-Cholamidepropyl) dimethylammonio-1-propane-sulphonate (CHAPS) (Sigma-Aldrich) as an amphoteric surfactant, and Polysorbate 80 (PS80) (Sigma-Aldrich) as a non-ionic surfactant. Surfactants dissolved in Tryptic Soy Broth (TSB) were serially diluted 10-fold and final concentrations of the surfactants were 0.0005%, 0.005%, 0.05%, and 0.5%.

Acetonitrile (HPLC-grade), formic acid, polysorbate 80 (PS 80), sodium chloride, sodium dihydrogen phosphate monohydrate, sodium hydrogen phosphate (anhydrous), sodium dodecyl sulfate (SDS) and tert-butanol were purchased from Sigma-Aldrich^® Denmark ApS (Brøndby, Denmark). Sodium hydroxide was purchased from Merck A/S (Hellerup, Denmark). Soluplus^®, an amphiphilic graft co-polymer based on polyethylene glycol, polyvinyl caprolactam and polyvinyl acetate, was kindly donated by BASF SE (Ludwigshafen, Germany). Tadalafil (TDF; purity 99%) was purchased from abcr GmbH (Karlsruhe, Germany). D-α-Tocopheryl polyethylene glycol 1000 succinate (Vitamin E TPGS) (NF grade) was kindly donated by Gustav Parmentier GmbH (Frankfurt am Main, Germany). If not stated otherwise, chemicals were of analytical grade. Simulated intestinal fluid (SIF) instant powder containing sodium taurocholate and lecithin was purchased from biorelevant.com (London, United Kingdom). Highly purified water used for the preparation of all dispersion- and acceptor media and aqueous UHPLC solvent was freshly prepared using a Milli-Q^® integral water purification system (Milli-Q^® Advantage A10^®; Merck Millipore, Merck A/S, Hellerup, Denmark).