Potassium hydrogen phosphate

The substances 3-aminopropyltrimethoxysilane (APTMS) and tetraethyl orthosilicate (TEOS) and the multiwalled carbon nanotubes (MWCNTs) (95%, L: 20–30 nm, D: 0.5–2 nm, W: 1–2 nm) were purchased from Sigma-Aldrich (Darmstadt, Germany; www.sigmaaldrich.com). Hypoxanthine, xanthine, caffeine, ferric chloride hexahydrate (FeCl₃ × 6H₂O), hexadecyl trimethyl ammonium bromide (CTAB), ethylene glycol (EG), sodium chloride, potassium chloride, sodium dihydrogen phosphate, and potassium hydrogen phosphate were purchased from Himedia (Mumbai, Maharashtra, India, http://www.himedialabs.com). Potassium ferricyanide, potassium ferrocyanide, sodium acetate, ethanol, methanol, ammonium hydroxide solution, acetic acid, hydrochloric acid, sulfuric acid, and nitric acid were obtained from SDFCL (India, http://www.sdfine.com). All of the reagents were of an analytical grade and were utilized without any further processing. A CH Instruments electrochemical workstation (CHI660D) (CH Instruments, USA) was used for all electrochemical experiments.

Graphite powder (≤20 µM), α-Al₂O₃, potassium permanganate, sodium nitrate, hydrogen peroxide (H₂O₂), LiClO₄, potassium chloride, sodium hydroxide, ruthenium hexamine chloride, dopamine, p-aminothiophenol, p-aminophenol, p-phenylenediamine, p-aminobenzoic acid and sulfanilic acid were purchased from Sigma-Aldrich. Sulfuric acid was purchased from Fisher-Scientific. Potassium ferrocyanide and potassium hydrogen phosphate were purchased from Hi-Media. Acetonitrile was purchased from SRL. All the chemicals were used as received without any purification. Ultrapure water from Siemens LaboStar (resistivity ~18.2 MΩ.cm) system was used to prepare phosphate buffer and other aqueous solutions.