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| Method | Preparation of FAMEs | GC operation | Standards used | Ref. |
|
| Transesterification | Redissolve total lipid extracts and elute neutral lipids and polar lipids with different solvents; after drying under nitrogen gas, derivatize to FAMEs and recover the FAMEs. | GC equipped with FID and Agilent CP-Wax 52 CB column. | (1) Internal standard: tripentadecanoin, C15:0 triacylglycerol, Sigma-Aldrich.
(2) Identification and quantification standard: Supelco® 37-component standards. | [34] |
| Add HCl and methanol to lipid extracts and heat mixture with hexane and methyl-tert-butyl ether; wash the upper organic phase with sodium hydroxide; aspirate two-thirds of the organic extracts and transfer to a sample vial. | GC equipped with FID and a special performance capillary column (Hewlett Packard model #HP-5 MS). | (1) Internal standard: hexadecane (Sigma-Aldrich #H6703) standard.
(2) Calibration standard: olive oil. | [35, 36] |
| Add H2SO4 to lipid extracts and heat; cool the sample to room temperature and mix with DI water to separate lipid extracts; move the lower part liquid into a vial. | GC equipped with FID and a Supelco NucolTM column (355 33-03A, film thickness) using Helium as the carrier gas (flow 20 mL·min−1). | (1) Internal standard: pentadecanoic acid (C15:0).
(2) Identification standard: authentic standards (Sigma-Aldrich, MO, USA). | [37, 38] |
| Add methanolic HCl to lipid extracts and flush headspace with nitrogen and seal tightly and heat; cool vials and add aqueous K2CO3; centrifuge and remove the upper phase and dry. | GC equipped with FID and a SGE Sol Gel-WaxTM capillary column using helium as the carrier gas. | (1) Identification standard: standard fatty acids (Nu-Chek Prep Inc., Elysian, MN).
(2) Quantification standard: heptadecanoic acid (C17:0). | [39] |
| Add chloroform containing heptadecanoic acid (C17:0), methanol, and sulfuric acid to each tube and heat; cool down, add DI, centrifuge, and separate the lower chloroform phase and filter for test. | GC equipped with FID and HP19091N-213 HP-INNOWax polyethylene glycol column. | (1) Internal standard: heptadecanoic acid (C17:0).
(2) Identification and quantification standard: 37 component FAME standard mix (Supelco, Bellefonte, USA). | [40] |
| Add BHT (butulated hydroxy toluene, 1% in methanol) to prevent oxidation prior to methylation. | GC equipped with FID and the capillary column DB-23 (Agilent Technologies) using helium as the carrier gas (1 mL·min−1, splitless). | (1) Quantification standard: C19:0 (nonadecanoic Acid 72332-1 G-F/analytical standard, Sigma-Aldrich).
(2) Identification standard: Supelco TM 37 Component FAME Mix, Sigma. | [41] |
| Add freshly prepared acetyl chloride/methanol (1 : 10), methanol into lipid extracts, and seal vials and heat; cool down and add K2CO3, hexane; centrifuge the samples and recover the hexane supernatant. | GC equipped with FID and a BPX70 capillary column (120 m × 0.25 mm internal diameter, 0.25 μm film thickness, SGE Analytical Science, Ringwood, VIC, Australia) using helium as carrier gas (1.5 mL·min−1). | (1) Internal standard: C23:0.
(2) Identification standard: a series of mixed and individual standards from Sigma-Aldrich. | [42, 43] |
| Mix H2SO4, methanol, THF, and lipid extracts; reflux the reaction mixture at 90°C with continuous stirring for 3 h; neutralize the mixture with NaHCO3 and extract it with hexane. | GC equipped with FID and HP-INNOWax column (30 m × 320 μm × 0.25 μm film of polyethylene glycol) using helium as carrier gas. | (1) The standard FAMES: C14:0, C16:0, C16:3, C18:0, C18:1, C18:2, C18:3, and C20:0.
(2) Supelco TM 37 Component FAME Mix, Sigma-Aldrich. | |
| Treat extracted lipids with methanolic sulfuric acid and heat; recover FAMEs in hexane; centrifuge the suspension and aspirate hexane, containing FAMEs, into new glass tube. | GC equipped with DB-5 capillary column (30 mm : 0.25 mm : 1 μm) and FID using helium as carrier gas (1 mL·min−1). | NISTIL.S database. | [44–46] |
|
| In situ transesterification | Add a mixture of methanol, sulfuric acid, and chloroform into dried cell biomass and heptadecanoic acid (C17:0) as an internal standard and heat; cool down, add DI water, mix, and settle; transfer the lower phase containing FAMEs to a clean vial and dry with anhydrous Na2SO4. | GC equipped with FID and SGE Sol Gel-WaxTM capillary column (30 m × 0.25 mm × 0.25 μm) using helium as the carrier gas. | (1) Identification standard: standard fatty acids (Sigma, MO).
(2) Quantification standard: internal standard (C17:0). | [47, 48] |
| There are many different ways to add a catalyst, such as methanolic hydrogen chloride, NaOMe and BF3, NaOMe, and tetramethyl guanidine and methanol; tridecanoic acid methyl ester (C13-FAME) as an internal standard and heat. | GC equipped with FID (Agilent 6890N, HP 5-MS column (Agilent, USA), 30 m 0.25 mm ID and 0.25 μm FT) using helium as the carrier gas (1.5 mL·min−1). | (1) C8–C24, SIGMA cat #18918
C13–C21, SIGMA cat #1896. | [49] |
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