Sodium nitrate

High purity flake graphite (300 mesh), sulfuric acid, hydrochloric acid, hydrogen peroxide, sodium nitrate, potassium permanganate, sodium borohydride, sodium hydroxide, cobalt chloride hexahydrate, and sodium hypophosphite monohydrate were obtained from Alfa Aesar Co., Ltd. (Tianjin, China). The chemicals used were analytical reagent. All experiments used ultrapure water.

Sodium nitrate, potassium permanganate, sulfuric acid, hydrogen peroxide (31.3% solution in water), hydrochloric acid (30% solution in water), and methanol (99.9%) were purchased from Fisher Scientific. All materials were used as received without further purification. Hummer's method was used to make graphene oxide [26 (link)].

Sodium nitrate (99.2%), potassium permanganate (99.4%), sulfuric acid (96.4%), hydrogen peroxide (31.3% solution in water), hydrochloric acid (30% solution in water) and methanol (99.9%) were purchased from Fisher Scientific. All materials were used as received without further purification.

Sucrose, sodium nitrate, potassium chloride, dipotassium phosphate, magnesium sulfate, iron (II) sulfate, and agar were purchased from Fisher Chemicals (Fair Lawn, NJ, USA). Enantiomerically pure (R)-(-)-mellein purchased from Cayman Chemical (Ann Arbor, MI, USA) with a listed purity of ≥98%, which was confirmed by GC-MS analysis (Chen, 2017 (link)), was used as an LC-MS/MS standard and for phytotoxicity testing with soybean seedlings. 3-Nitropropionic acid for use as an LC-MS/MS standard was purchased from Sigma-Aldrich (Vienna, Austria). For culture medium preparation and phytotoxicity assays, reverse osmosis water was purified by a Barnstead E-Pure Ultrapure Water Purification System (Thermo Scientific, Marietta, OH, USA).
Reagents for LC-MS/MS analysis consisted of LC-MS grade ammonium acetate and glacial acetic acid purchased from Sigma-Aldrich (Vienna, Austria), LC-MS Chromasolv grade methanol purchased from Honeywell (Seelze, Germany), HiPerSolv Chromanorm HPLC gradient grade acetonitrile purchased from VWR Chemicals (Vienna, Austria), and reverse osmosis water purified using a Purelab Ultra system (ELGA LabWater, Celle, Germany).

All chemicals were of analytical grade and purchased from Sigma-Aldrich (Vale Road, Arklow, Co. Wicklow, Ireland), unless otherwise stated. Sodium meta-arsenite (NaAsO₂), iron sulphate heptahydrate (FeSO₄·7H₂O) (Fisher Scientific, Leicestershire, UK), magnesium sulphate (MgSO₄) (Fisher Scientific), potassium dihydrogen phosphate (KH₂PO₄), manganese sulphate monohydrate (MnSO4·H₂O), and sodium nitrate (NaNO₃)were used to prepare stock solutions at concentration 1000 µg mL⁻¹ in double deionised water (HPLC grade). Working standards were prepared by serial dilutions. Acetic acid (99.8%) (Sharlab S.L., Barcelona, Spain) was used to adjust the pH. Trimethanolamine ((HOCH₂CH₂)₃N), citric acid, (HOC(COOH)(CH2COOH)2) ascorbic acid (C6H8O6), potassium iodate (KIO₃), leucomalachite green dye (C₆H₅CH[C₆H₄N(CH₃)₂]₂), sodium triacetate trihydrate (C₂H₃NaO₂·3H₂O) were prepared by weighing out an appropriate amount and dissolving it in double deionised water. Hydrochloric acid (38%) (Sharlab S.L.) was used to prepare hydrochloric acid solutions with various concentrations in double deionised water. Double deionized water was used for dilution of reagents and samples.