Diphenylamine

The solvents used for GC-MS and HPLC-PDA were of analytical grade. Methanol and acetonitrile were obtained from Fisher Chemical (Fisher Bioblock, Belgium). Water was purified by a Milli-Q system obtained from Merck Millipore (Darmstadt, Germany).
Triethylammonium (TEA) phosphate buffer 1M was purchased from Sigma (Zwijndrecht, Belgium) and was diluted 1/40 immediately before use. Diphenylamine used as external standard was obtained from VWR International (Leuven, Belgium). Solvents for ESI-HRMS were of ULC-grade and were purchased from Biosolve (Valkenswaard, the Netherlands).
acetonitrile for ESI-LCMS was purchased from Merck (Darmstadt, Germany) and was of HPLC grade. Water was obtained from a Millipore Synergy UV apparatus (Billerica MA, USA). Formic acid was purchased from Sigma-Aldrich and was of mass spectrometry grade. Deuterated dimethyl sulfoxide (0.03%, v/v tetramethylsilane) for NMR was obtained as ampoules (750 µL) from Euriso-Top (Saint Aubain, France).

Certified reference components and general chemical reagents were obtained from Cayman Chemical (Michigan, USA). Solvents used for GC-MS and HPLC-PDA were of analytical grade.
Methanol, acetonitrile and hydrochloric acid (37 %) were obtained from Fisher Chemical (Fisher Bioblock, Belgium). Water was purified by a Milli-Q system obtained from Merck Millipore (Darmstadt, Germany). Triethylammonium (TEA) phosphate 1 M was purchased from Sigma (Zwijndrecht, Belgium) and was diluted 1/40 immediately before use. The external standard diphenylamine was obtained from VWR International (Leuven, Belgium). N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA) and N-methyl-bis(trifluoroacetamide) (MBTFA) were purchased from Machery-Nagel (Germany). NMR analysis and associated sample preparation: deuterated solvents for NMR were purchased from Euriso Top (St. Aubain, France).
Tetramethylsilane was of NMR grade and was acquired from Acros Organics (Geel, Belgium).
Dichloromethane was purchased from Sigma-Aldrich and was of HPLC grade. hydrochloric acid and sodium hydroxide were purchased from Acros Organics (Geel, Belgium) and were of ACS grade. Ultrapure water was obtained from a Millipore Synergy UV apparatus (Billerica MA, USA).