Identification of very long-chain (>C24) fatty acid methyl esters using gas chromatography coupled to quadrupole/time-of-flight mass spectrometry with atmospheric pressure chemical ionization source

Abstract

Gas chromatography coupled to a quadrupole time-of-flight mass analyzer (QTOF) with an atmospheric pressure chemical ionization (APCI) source has been tested to study the ionization and mass spectrometric behavior of long-chain and very long-chain polyunsaturated fatty acids (LC-PUFAs, C18-24; VLC-PUFAs, >C24). The protonated molecule ([M+H] +), measured at accurate mass, became the base peak of the spectrum for all the studied compounds and was promoted by the addition of water into the source. This fact overcame the existing difficulties for the identification of VLC-PUFAs when using an electron ionization source (EI). The extensive fragmentation of PUFAs in this source is the main drawback due to the fact that since reference standards are not commercially available, final identification relies on retention time estimation. The application of GC-APCI-QTOF to the screening of lipid extracts from the eyes of different fish species added confidence to the identification of several VLC-PUFAs. Further investigation of ion ratios allowed to predict the position of key double bonds enabling the classification of VLC-PUFAs as w3 or w6 compounds. VLC-PUFAs spectra found in biological samples were compared to those obtained from corresponding peaks found in heterologous expression experiments of fish's Elovl4.

Identification of new, very long-chain polyunsaturated fatty acids in fish by gas chromatography coupled to quadrupole/time-of-flight mass spectrometry with atmospheric pressure chemical ionization

“…The three fractions where VLC-PUFAs were detected in previous analyses, namely SM, PC and CE, were scrapped off the plate [33], eluted in chloroform:methanol (2:1, v/v) containing BHT (0.01%, w/v), and used to prepare fatty acid methyl esters (FAMEs) [34]. Methyl esters (ME) were stored in hexane/BHT (0.01%) under nitrogen at -20ºC (for more details see Garlito et al [11]). Prior to the analysis by GC-APCI-QTOF MS and GC-APCI-IMS-QTOF MS samples were dried with a gentle flow of N 2 and reconstituted in 50 µL of hexane.…”

“…As in a previous work [11], an Agilent 7890 N gas chromatograph (Palo Alto, CA, USA) equipped with an Agilent 7683 autosampler was coupled to a quadrupole orthogonal acceleration time-of-flight mass spectrometer, Xevo G2 QTOF (Waters Corporation, Manchester, UK), equipped with APGC v2.0 as ionization source, working in positive APCI mode. A fused silica VF-5HT capillary column with a length of 15 m × 0.32 mm i.d.…”

“…From our previous experience [11] and taking into account the literature regarding PUFAs analysis by GC [8,24,25,27], three chromatographic columns (DB-5MS 60 m × 0.25 mm, 0.25 µm; BD-EN14103 30 m × 0.32 mm, 0.25 µm; VF-5HT 15m × 0.32 mm, 0.10 µm) were tested. The best results were obtained with the VF-5HT column, which was selected to continue the work.…”

“…The existence of very long-chain polyunsaturated fatty acids (VLC-PUFAs) ranging from 26 to 36 carbons in length in mammal spermatozoa and vertebrate retina was reported in 1986-87 by Poulos et al [1,2] and Aveldaño and Sprecher [3]. Since then, low concentrations of up to C38 VLC-PUFAs have been reported in phosphatidylcholine (PC) of human brain [4]; triacylglycerides (TG) and cholesterol esters (CHE) of mammalian testis [5]; sperm and brain of mammals; PC, sphingomyelin (SM) and cerebrosides (CE) of human retina [6][7][8][9], and PC of fish retina [10,11]. VLC-PUFAs have been associated with macular dystrophy [6] and Zellweger's syndrome [4], and are considered essential for the development of the nervous system, retinal function and reproduction in vertebrates [10,[12][13][14].…”

Análisis de compuestos endógenos y exógenos en productos de acuicultura mediante técnicas analíticas avanzadas

“…✓ q/Q within accepted tolerances.96T. Portolés et al, Chemosphere 179 (2017)[242][243][244][245][246][247][248][249][250][251][252][253] The developed strategy faces the "universal" pesticide analysis in aquaculture field by means of combined use of LC-QTOF MS and GC-QTOF MS for screening, followed by confirmation and quantification by GC-(APCI)MS/MS with QqQ, as most pesticide detected in the screening were GC-amenable. The strategy proposed is among the most comprehensive and informative in the pesticide analysis context as it covers a large list of pesticides from different families.…”