Formaldehyde h2 solution

Sodium acetate, ferric chloride (FeCl₃), ferrous chloride (FeCl₂), sodium cyanoborohydride (NaBCNH₃), and trifluoroacetic acid (TFA) were obtained from Sigma-Aldrich (St. Louis, MO, USA). Acetonitrile (MeCN) was bought from Merck (Seelze, Germany). Ammonium hydrogen carbonate (NH₄HCO₃), hydrochloric acid, sodium hydroxide, sodium dodecyl sulphate (SDS), and ethanol were purchased from J. T. Baker (Phillipsburg, NJ, USA). Formaldehyde-D₂ solution (20% solution in D₂O) was purchased from Isotec Corp. (Miamisburg, OH, USA), while formaldehyde-H₂ solution (36.5%–38% in H₂O), potassium chloride (KCl), sodium chloride (NaCl), sodium dihydrogen phosphate (NaH₂PO₄), potassium dihydrogen phosphate (KH₂PO₄), dimethyl sulfoxide (DMSO), formic acid (FA, 98%–100%), and iodoacetamide (IAM) were purchased from Sigma (St. Louis, MO, USA). Trypsin was purchased from Promega (Madison, WI, USA). The protein concentration of cell lysate was determined by Bradford assay based on the measurement BSA calibration curve (Thermo, Rockford, IL, USA). Deionized H₂O with a resistance of 18.2 MΩ was obtained using a Millipore water system.

Serotonin (hydrochloride form), sodium cyanoborohydride (NaBH₃CN), sodium acetate, and tryptophan were obtained from Sigma–Aldrich (St. Louis, MO, USA). The LC–MS grade solvents, including acetonitrile (MeCN), methanol (MeOH), and 0.22 μm PTFE filters, were bought from Merck (Seelze, Germany). Sodium hydroxide and hydrochloric acid were purchased from J.T. Baker (Phillipsburg, NJ, USA) to adjust the buffer pH. Formaldehyde-D₂ solution (20% solution in D₂O) was purchased from Isotec Corp. (Miamisburg, OH, USA), and formaldehyde-H₂ solution (36.5–38% in H₂O), 5-HTP and formic acid (FA, 98–100%) were purchased from Sigma (St. Louis, MO, USA). Deionized H₂O with a resistance of 18.2 MΩ was obtained using a Millipore water system.