γ aminobutyric acid 2 2 3 3 4 4 d6

High performance liquid chromatography (HPLC) grade acetonitrile and methanol were purchased from Thermo Fisher Scientific (Waltham, MA, USA). Formic acid (> 98.0%), GABA (≥ 99.0%), γ-aminobutyric acid-2,2,3,3,4,4-d₆ (97.0% atom D), l-glutamic acid (> 99.0%) and l-glutamic acid-2,3,3,4,4-d₅ (97.0% atom D, 98.0%) were obtained from Sigma-Aldrich. The AccQ Tag Ultra derivatization kit were purchased from Waters (Milford, MA, USA). Water was purified in a Milli-Q water purification system from Millipore (Burlington, MA, USA).

Uric acid, L-tryptophan, L-alanine, L-valine, L-leucine, L-isoleucine, glycine, l-serine, succinic acid, fumaric acid, malic acid, 2-ketoglutaric acid, L-glutamic acid, D-ribose, sodium 2-hydroxybutyrate, 3-hydroxybutyric acid, 2-isopropylmalic acid, formic acid, serotonin, γ-aminobutyric acid-2,2,3,3,4,4d6, 21-deoxycortisol, 11-deoxycortisol, oleic acid, cis-4,7,10,13,16,19-docosahexaenoic acid, cis-10-nonadecenoic acid (C19:1n9c) and sodium taurochenodeoxycholate were purchased from Sigma-Aldrich (St. Louis, MO, USA). Taurocholic acid was obtained from Steraloids (Newport, RI, USA). p-Cresyl sulfate potassium salt and arachidonic acid were supplied from Toronto Research Chemicals (North York, ON, Canada). Urea, HPLC-graded acetonitrile, methanol and isopropanol were obtained from Fisher Scientific (Hampton, NH, USA). Water was purified in-house using a Milli-Q Advantage A10 water purification system (Millipore, Bedford, MA, USA). Palmitic acid, cis-9,12-linoleic acid, 2-aminobutyric acid, pyridine (HPLC grade) with AcroSeal and N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA) were acquired from Acros Organics (Morris Plains, NJ, USA).