Serotonin d4 hydrochloride

Prior to analysis, samples were thawed and thoroughly mixed (Classic Advanced Vortex Mixer, Velp Scientifica, Italy). Then, 50 µL of each sample was treated with 10 µL of sodium metabisulfite solution, 950 µL of mobile phase B, 2.5 µL of deuterated histamine d4 (internal standard, IS), at a concentration of 1 µg/mL and 2.5 µL of a 1 µg/mL deuterated serotonin d4 solution, mixed and centrifuged (Centrifuge 5417R, Eppendorf, Germany) at RCF 24,104 × g for 10 min. Next, 500 µL of supernatant was taken for LC–MS/MS analysis. Deuterated histamine and deuterated serotonin solutions were prepared by diluting stock standard solutions in methanol (Serotonin d4 hydrochloride, Toronto Research Chemicals, Canada, and Histamine- α,α,β,β d4 dihydrochloride Sigma Aldrich, US).

Imidacloprid (IMI) was purchased from Kanto Chemical Co., Inc. (Tokyo, Japan). DA, 3-methoxytyramine HCl (3-MT), 3-methoxytyramine-d4 HCl, and serotonin were purchased from Sigma-Aldrich (St. Louis, MO, USA). serotonin-d4 hydrochloride and histamine were purchased from Toronto Research Chemicals, Inc. (Toronto, ON, Canada), and dopamine-d4 and histamine-d4 were purchased from WATARAI Co., Ltd. (Kanagawa, Japan). DPP, which was originally purchased from Sigma Aldrich (St. Louis, MO, USA), was donated by Associate Professor Shuuichi Shimma, Department of Biotechnology, Graduate School of Engineering, Osaka University. Corn oil and formic acid were purchased from Wako Pure Chemicals Co., Inc. (Tokyo, Japan); dimethyl sulfoxide (DMSO) was purchased from Nacalai Tesque, Inc. (Kyoto, Japan); triethylamine (TEA) was purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan); and methanol (MeOH) was purchased from Kanto Chemical Co., Inc.