Tetraethyl orthosilicate teos

Pluronic P123 (≥98%) (Sigma-Aldrich Chemie, Schnelldorf, Germany), (3-aminopropyl)triethoxysilane (APTES) (≥98%) (Sigma-Aldrich, Saint Louis, MO, USA), hexadecyltrimethylammonium bromide (CTAB) (≥98%) (Sigma-Aldrich Chemie, Schnelldorf, Germany), tetraethyl orthosilicate (TEOS) 98% (Fisher Scientific, Loughborough, UK), hydrochloric acid (37%) (Valerus, Bulgaria) and sodium hydroxide (NaOH) (Merck, Darmstadt, Germany) were used without further purification. Furfural (≥98%) and diethyl H-phosphonate (≥95%) were Sigma-Aldrich (Sigma-Aldrich Production GmbH, Product Brand Fluka, Buchs, Switzerland) products and were distilled prior to use. Toluene and diethylene glycol dimethyl ether (diglyme) (Sigma-Aldrich, Saint Louis, MO, USA) were dried via azeotropic distillation. Deionized distilled water was used in the preparation of all solutions.

Tetraethyl orthosilicate (TEOS, 98%), and ammonia (NH3, 28% w/w) from Alfa Aesar (Karlsruhe, Germany). Ethanol (EtOH, ABS) used for the different stages of the synthesis and work-up was purchased from ChemLab (Zedelgem, Belgium). The water (18 MΩ cm pure water) was of Milli-Q Gradient system (Millipore Corp) to keep conditions constant. For the glass slides treatment, a 1:4 piranha solution (H₂O₂/H₂SO₄) was used. Hydrogen peroxide (33.3%) was purchased from VWR Chemicals and sulphuric acid (95–97%) was received from Merck. All reagents were used as received.

BA standards of histamine, putrescine, cadaverine, spermidine, spermine, 2-phenylethylamine, tyramine, isoamylamine and n-heptylamine (purity > 97%) were obtained from TCI Europe chemicals (Zwijndrecht, Belgium) and Across chemicals (Geel, Belgium). Tetraethyl orthosilicate (TEOS) (98%) from Alfa-Aesar (Kandel, Germany), 3-mercaptopropyltrimethoxysilane (MPTS) (95%) and (Diethylphosphatoethyl)triethoxysilane (DPETS) (95%) from ABCR (Karlsruhe, Germany), were used as precursors for the synthesis of functionalized silica. Bis[3-(silsequioxy)propyl] tetrasulfide was kindly donated by Sikemia (Montpellier, France). Triblock copolymer Pluronic P123 (Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)) from Aldrich (St. Louis, USA), and polyethylenglycol (PEG) 20,000 from Alfa-Aesar, were used as surfactants for the synthesis of silica by sol–gel route. Hydrochloric acid (37%), ethanol (> 99.8%), and nitric acid (65%) and dichloromethane (> 99.8%) from VWR (Fontenay sous Bois, France), and sulfuric acid (98%), Triphenylphosphine (99%), dioxane (99.8%), meta-chloroperoxybenzoic acid (99%) and diethylethoxymethylenemalonate (DEEMM), from Sigma-Aldrich (Steinheim, Germany), and ammonia (30%) from Carlo-Erba (Val de Reuil, France), were obtained.

All compounds were used as received. 98% l-lysine, 99% hexanoic acid, 97% 3-aminopropyltrimethoxysilane (APTMS), 95% O-(2-carboxyethyl)-O′-methyl-undecaethylene glycol (CMUG), 99% potassium phosphate monobasic (KH₂PO₄), and 98% potassium phosphate dibasic (K₂HPO₄) were purchased from Sigma-Aldrich. HPLC grade acetonitrile and 99.9% tetrahydrofuran (THF) were purchased from EMD Millipore. 99.8% methanol (MeOH), ACS grade toluene, and biotechnology grade trifluoroacetic acid (TFA) were purchased from VWR. 95% 3-aminopropyldimethylethoxysilane (APDMES) was purchased from Gelest. 99% ninhydrin, 95% fluorescamine, and 99.9% tetraethyl orthosilicate (TEOS) were purchased from Alfa Aesar. 99.8% deuterium oxide (D₂O) was purchased from Acros Organics. 98% propylamine was purchased from TCI.