Analysis and Classification of Common Vegetable Oils

Abstract

The analysis of fatty acids from common vegetable oils was investigated for application to forensic casework. A base-catalyzed transesterification of the fatty acids to fatty acid methyl esters using tetramethylammonium hydroxide was simple, rapid, straightforward and inexpensive. Canola, corn, olive, peanut, safflower, soybean and sunflower oils were able to be classified based on their fatty acid methyl ester profiles. Using gas chromatography-mass spectrometry, the detection limits for canola, corn, olive, peanut and safflower oils were determined to be 0.4 mg/mL or less and 0.2 mg/mL or less for soybean and sunflower oils.

A quick discrimination of vegetable oil by solid-phase microextraction method

“…For analysis of saponifiable constituents as FAMEs, the protocol reported by Pitts and Thomson [10] was adopted with slightly modification. The oil remaining after thermal desorption or that was freshly added to the SPME fiber was recovered with 100 mL of diethyl ether (to check the SPME fiber resistance in Section 3.4, acetone was used); 50 mL of 25% (w/w) TMAH in methanol was then added.…”

“…Therefore, organic solvents, which have hydrophobic properties, are incompatible with the fibers because the solvent is absorbed by the fiber materials, resulting in swelling [13]. We first chose diethyl ether as a recovery solvent to obtain fine data for the FAMEs following a method described in a previous report [10]. However, this solvent was found to be unsuitable for our study.…”

“…When a SPME fiber that was immersed into the vegetable oil is inserted directly into the injection port of a GC, the unsaponifiable constituents will vaporize in the injection port. Meanwhile the saponifiable constituents remain on the needle of the SPME device, and the remaining oil can then be recovered and further analyzed on GC as FAMEs using a base-catalyzed trans-esterification technique [6][7][8][9][10]. In summary, thermal desorption is applied to separate the unsaponifiable constituents from oils in the SPME method, thus it becomes a quick method saving time and operations.…”

GC-FID methodology validation for the fatty esters content determination in biodiesel with hexadecyl acetate as the internal standard

“…In the case of polyunsaturated chains, the double bonds are not conjugated, that is, they are separated by a methylene group. 18 The most abundant fatty acids are palmitic (C16:0), stearic (C18:0), oleic (C18:1), and linoleic (C18:2), Figure 1. In the CX:Y notation, X is the number of carbons, and Y, the number of double bonds.…”

“…In the CX:Y notation, X is the number of carbons, and Y, the number of double bonds. 15,16,18 Examples of methyl biodiesels from different sources are presented in Table 1. 16 Biodiesel must be in accordance with a set of quality parameters to be employed, that includes purity and impurities contents; performance characteristics, as cetane number, oxidative stability; and physical properties, as viscosity, and specific mass.…”