A Method for Forensic Identification of Vegetable Oil Stains—Rapid Analysis of Carboxylic Acids with Methyl Esterification Using Purge-and-Trap Gas Chromatography/Mass Spectrometry

Abstract

A simple method using purge-and-trap gas chromatography/mass spectrometry (P&T-GC/MS) for forensic examination of oil stains was studied. Carboxylic acids, chosen as target components for discrimination of oil samples, were extracted from stains with ether, methyl esterified by tetramethylammonium hydroxide, and analyzed by P&T-GC/MS. Vegetable oils were discriminated according to their carboxylic acid compositions. Carboxylic acid composition was independent of the substrate material of the stain. Although the carboxylic acid composition of the oil changed on exposure to sunlight, identification of oil was possible for oil stains that had been in the shade, if analysis was made within 20 days.

Rapid Discrimination of Fatty Acid Composition in Fats and Oils by Electrospray Ionization Mass Spectrometry

“…Fatty acid compositions play an important role in forensic science, sometimes serving as evidence in criminal investigations into the causes of fires resulting from arson or spontaneous ignition. [1][2][3] Discrimination between control oil samples, taken from a suspect or victim, and oil samples collected at crime scenes is required, as is the identification of their types in certain cases. When a control fat or oil is unknown, the fatty acid composition (including the degree of unsaturation) and the varying chain lengths are useful for establishing the distinction between liquid oils and solid fats; the classification into drying, semi-drying, and nondrying oils; and the discrimination of types of fats and oils.…”

“…When a control fat or oil is unknown, the fatty acid composition (including the degree of unsaturation) and the varying chain lengths are useful for establishing the distinction between liquid oils and solid fats; the classification into drying, semi-drying, and nondrying oils; and the discrimination of types of fats and oils. Fatty acid composition is frequently analyzed by gas chromatography (GC) [4][5][6][7][8][9][10] and gas chromatography-mass spectrometry (GC-MS) [1][2][3][11][12][13][14] of saponifiables 1,2,4,5,11-13 for their classification, or for the discrimination of fats and oils. When fats and oils are saponified, saponifiables are obtained in the form of fatty acid salts, such as potassium salts in an aqueous layer.…”

A Review of the Analysis of Vegetable Oil Residues from Fire Debris Samples: Analytical Scheme, Interpretation of the Results, and Future Needs

“…With Gélin, he also used a GC‐MS for the peak identification (38). Ehara et al (18) used a GC‐MS equipped with a purge‐and‐trap system and an HP Innowax column. Pitts and Thomson (39) used a GC‐MS equipped with a DB‐WAX column and obtained excellent separation.…”

“…In more particular forensic applications, Ehara et al (18) used ether to extract vegetable oil stains in their laboratory experiments. Coulombe (19) used ethyl ether to extract VOR from a burned towel.…”

“…This last step is not performed because it has jeopardized the cleanliness of the GC injector in prior experiments (R. Keto, personal communication, August 2004). Ehara et al (18) use tetramethylammonium hydroxide (TMAH) to proceed to the transesterification to FAMEs. Pitts and Thomson (39) use TMAH in their experiment on the classification of vegetable oils.…”