Cellulose acetate syringe filter

Neat ritonavir and ritonavir-ASD were provided by AbbVie Germany, Ludwigshafen, Germany. The ritonavir-ASD was prepared as extrudate beads by hot melt extrusion on a co-rotating twin-screw extruder, and composed of ritonavir (15%), copovidone (74%), sorbitan monolaurate (10%), and colloidal silicon dioxide (1%). The purity of the ingredients was according to the compendial specifications (Ph.Eur./USP). The absence of API-related crystallinity in the ASD was confirmed by polarized light microscopy (Model DMLM, Leica Microsystems, Wetzlar, Germany). Tri-potassium phosphate (Alfa Aesar, Kandel, Germany), tri-potassium citrate (Carl Roth, Karlsruhe, Germany), and sodium hydroxide (VWR Chemicals, Darmstadt, Germany) were used for the buffer concentrate. Lecithin, 1-decanol, and sodium taurocholate were obtained from Alfa Aesar (Kandel, Germany). Glitter powder was purchased from Jofrika Cosmetics, Bergisch-Gladbach, Germany. The high performance liquid chromatography HPLC chemicals consisted of methanol (VWR Chemicals, Darmstadt, Germany), acetonitrile (VWR Chemicals, Darmstadt, Germany), and demineralized water (Merck Milli-Q, Darmstadt, Germany). Samples for HPLC were filtered through a 0.45 µm cellulose acetate syringe filter (VWR Chemicals, Darmstadt, Germany).

Samples were taken aseptically and prior to all other samples following a previously described protocol^{32 (link)}. Briefly, water was sampled in sterile 1 L Schott glass bottles in immediate vicinity to the collected F. vesiculosus thalli (3 algal replicates). Before sampling, algal thalli were rinsed with seawater previously sterile-filtered through 0.2 µm cellulose acetate syringe filters (VWR International GmbH, Darmstadt, Germany). For sampling of algal surface-associated microbiota, approximately 15 cm² of algal surface per replicate were swabbed using sterile cotton swabs. We sampled 3 different regions of the sporophyte, i.e. tip, thallus and the whole surface sample (incl. both tip and thallus regions). After sampling, all samples were immediately placed on ice and the cotton swabs were frozen at −80 °C upon arrival in the lab. 0.5 L of all 3 water samples were filtered through cellulose nitrate filters (pore size 0.45 µm, Whatman) and filters were immediately stored at −80 °C freezer.

Four APs that are frequently used in a wide range of OTC aqueous FPPs: cetylpyridinium chloride (CC), methylparaben (MP), sodium benzoate (SB), phenoxyethanol (PE) (Fisher Scientific) were used in this study. These four APs are representatives from different classes of APs (i.e., quaternary ammonium compounds, parabens, acids and their salts, and alcohols, respectively).
CC, SB and PE were prepared in HPW (Sigma-Aldrich). As MP is a water insoluble agent, stock solution of 5% w/v MP was prepared in propylene glycol (heated to approximately 45°C to dissolve completely) and subsequently used to prepare additional concentrations in HPW where required. All aqueous AP solutions were prepared on the day of use, sterilized using sterile 0.2 μm cellulose acetate syringe filters (VWR International), to achieve their highest recommended usage concentrations: 0.5% w/v CC; 0.4% w/v MP; 0.5% w/v SB; 1% v/v PE.