Sulfuric acid

Cylindrospermopsin standard (purity > 95%) was purchased from Eurofins/Abraxis (Eurofins/Abraxis, Warminster, PA, USA). Methanol (99.9% HPLC grade), Ferrozine (97%), and peroxidase from horseradish (type II) were obtained from Sigma-Aldrich (Sigma-Aldrich, São Paulo, SP, Brazil). Acetic acid glacial (99.7% HPLC grade) was purchased from J.T Baker (J. T. Baker, Brazil). Hydroxylamine hydrochloride (96%) and ammonium hydroxide (27% v/v) were purchased from Synth (Synth, Diadema, SP, Brazil). Ammonium acetate (97%), N,N-Diethyl-p-phenylenediamine sulfate salt (98%), sodium phosphate dibasic (98%), sodium phosphate monobasic (98%), and hydrogen peroxide (35% v/v) were obtained from Neon (Neon, Suzano, SP, Brazil). Sodium sulfite (98%), sulfuric acid (98% v/v), hydrochloric acid (36.5% v/v), iron (II) sulfate heptahydrate (99%) and iron (III) chloride hexahydrate (97%) were purchased from Dinâmica (Dinâmica, Indaiatuba, SP, Brazil).
All solutions used in the experiments were prepared using ultrapure water (Milli-Q Reference water purification system, C79625, Merck Millipore, Darmstadt, Hesse, Germany).

Sodium tetrachloropalladate (Na₂PdCl₄, 98 wt% purity) and the Nafion^® 117 cationic exchange membrane were purchased from Sigma-Aldrich (Jurubatuba, Brazil). Sodium hydroxide (97 wt% purity, P.A.-ACS), sulfuric acid (98 wt% P.A.), formic acid (85 wt% purity, P.A.-ACS), glycerol (99.5 wt% purity, P.A.-ACS), and 2-propanol (99.5 wt% purity, P.A.-ACS) were acquired from Dinâmica (São Paulo, Brazil). For titration, a solution 1 mol L⁻¹ NaOH (Sigma-Aldrich, Titripur^®) and 1 mol L⁻¹ HCl (Sigma-Aldrich, Titripur^®) were used for acid and alkali quantification. Vulcan XC-72R was purchased from Cabot Corporation (Boston, Massachusetts, USA). Nafion^® (5 wt% in a mixture of aliphatic alcohols) was acquired from IonPower (New Castle, DE, USA).

Medical-grade PEEK (Victrex^® TecaPEEK Classix White) materials used in this study were provided by Ensinger (São Leopoldo, RS, Brazil). Disk samples with dimensions of ɸ20 × 8 mm were prepared for surface characterization, immersion tests and in vitro studies. Aluminum carbide sandpaper (Al4C3) (600#, 1200# and 2000#) was provided by Deerfos^® (Maringá, Brazil). Sulfuric acid 98% was obtained from Dinâmica^® (Sao Paulo, Brazil) and hydrogen peroxide 35% from Neon^® (Sao Paulo, Brazil).