2 chloro 1 methylpyridinium iodide cmpi

HPLC‐grade hexane, acetonitrile (ACN), 2‐propanol, chloroform (CHCl₃), methanol (MeOH), ammonium hydroxide (>25%), formic acid (>99%), acetic acid (>99%), heptadecanoic acid, and ammonium acetate were from CNW (Düsseldorf, Germany). Triethylamine (TEA) and N,N‐diethyl‐1,2‐ethanediamine (DEEA) were from Shanghai Aladdin Reagent Co., Ltd. 2‐Chloro‐1‐methylpyridinium iodide (CMPI) was from Sinopharm Chemical Reagent Co., Ltd. 1,2,3‐Tri‐(heptadecenoyl)‐glycerol (TAG‐17:1/17:1:/17:1) was from Avanti Polar Lipids, Inc. (Alabama, USA). Other standards were from Sigma‐Aldrich (St. Louis, MO, USA), unless otherwise stated. Other reagents were analytical grade from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ultra‐pure water (Milli‐Q, Millipore, Bedford, MA, USA) was used for all experiments.

All fatty acid standards were purchased from Sigma (St. Louis, MO, USA) and J&K Chemical (Beijing, China). Analytical grade formic acid (FA), ethyl acetate (EA), triethylamine (TEA), 2-chloro-1-methylpyridinium iodide (CMPI), and DMED were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Isotope labeling reagent of d₄-DMED was synthesized according to our previously reported method [27 (link)]. HPLC-grade acetonitrile (ACN) and methanol were purchased from TEDIA Co., Inc (Fairfield, OH, USA). Water used for analysis was purified by a Milli-Q apparatus (Millipore, Milford, CT, USA). Stock solutions of TEA (20 mmol/L), CMPI (20 mmol/L), DMED (40 mmol/L), and d₄-DMED (40 mmol/L) were prepared in HPLC-grade ACN. Stock solutions of standard organic acids were prepared in HPLC-grade ACN with a concentration of 1.0 mg/mL for each and stored at −20 °C until analyzed.