Tetracosanoic acid

Isooctane and methanol (chromatographically pure) were purchased from JT Baker (Phillipsburg, NJ, USA). Sodium hydroxide, sulfuric acid, and anhydrous sodium sulfate (analytical grade) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China); EPA methyl ester (batch number, E6540099), DHA methyl ester (batch number, I2920075), EPA (batch number, H0660050), and DHA (batch number, I2950035) were provided by Shanghai Anpu Experimental Technology Co., Ltd.(Shanghai, China); and tetracosanoic acid (C23:0, purity ≥ 99.0%) and methyl ester (batch number, BCBV4775; purity ≥ 99.0%) were purchased from Sigma. Bet's Xiaofu cod-liver oil (in capsule form) was purchased from Guangdong Meikang Health Products Co., Ltd. (Guangzhou, China). The approved document no. was Guojian G20130699 by the State Food and Drug Administration.

The following chemicals were purchased from Tokyo Chemical Industry (Tokyo, Japan): n-octanoic acid (C8:0), lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0), cis-9-hexadecenoic acid (C16:1), stearic acid (C18:0), γ-linolenic acid (C18:3), cis-5,8,11,14,17-eicosapentaenoic acid (EPA; C20:5) and arachidonic acid (C20:4). Decanoic acid (C10:0), 9-decenoic acid (C10:1), oleic acid (C18:1), arachidic acid (C20:0), all-cis-7,10,13,16,19-docosapentaenoic acid (DPA, C22:5), docosanoic acid (C22:0), tetracosanoic acid (C24:0), hexacosanoic acid (C26:0), DAABD-AE, N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC), 4-(dimethylamino) pyridine (DMAP) and perfluorooctanoic acid (PFOA) were purchased from Sigma-Aldrich (Taufkirchen, Germany). The following deuterium or ¹³C labeled analogs used as IS were purchased from Cambridge Isotopes Laboratories (Tewksbury, MA, USA): ¹³C₄-C8:0, d₃-C10:0, d₃-C12:0, d₃-C14:0, d₄-C16:0 and d₃-C18:0. PRA, PHA, d₃-PRA, d₃-PHA, d₄-C22:0, d₄-C24:0, and d₄-C26:0 were obtained from Dr. H. J. Ten Brink (Vrije Universiteit Medical Center, Amsterdam, The Netherlands). LC-MS/MS grade acetonitrile and water were purchased from Merck (Darmstadt, Germany). Merck also supplied us with HPLC grade hexane, toluene, and heptane.