Nano Liquid Chromatography Directly Coupled to Electron Ionization Mass Spectrometry for Free Fatty Acid Elucidation in Mussel

Abstract

Recently the miniaturization of liquid chromatography (LC) systems and progresses in mass spectrometry instrumentation have enabled direct introduction of the effluent coming from a nanoLC column into the high-vacuum region of an electron ionization source. In the present research, a nanoLC system was directly coupled to an electron ionization mass spectrometer (EI-MS) without any interface or modification of the ion source. The advantage with respect to atmospheric pressure ionization techniques, normally coupled with LC, is major identification power because of a more extensive and reproducible fragmentation pattern, without any matrix effect or mobile-phase interference. In particular, a nanoLC/EI-MS method was developed for elucidation of the free fatty acid profile in mussel samples, avoiding a previous derivatization step, required when gas chromatographic analysis is involved. A total of 20 fatty acids were reliably identified through the comparison with commercial libraries. A quantitative determination was also carried out by using the response factors approach along with the internal standard method, allowing for quantification of 14 fatty acids. Among them, palmitic acid resulted the most abundant, followed by ω6 arachidonic acid. The quantitative data were compared with those obtained by a well-established technique, such as gas chromatography with flame ionization detection (GC-FID). Both nanoLC/EI-MS and GC-FID methods were validated and similar results were obtained in terms of limit of detection and quantification, resulting in the picomole range, and sensitivity as well was not significantly different, as demonstrated by comparing the slope values of the calibration curves (p < 0.05, from a t-test).

Evaluation of matrix effect in one‐dimensional and comprehensive two‐dimensional liquid chromatography for the determination of the phenolic fraction in extra virgin olive oils

“…Unfortunately, their use is not widespread due to a lack of commercial standards or their high cost [39]. Other established approaches for overcoming such aspects are represented by the use of nanoLC‐EI‐MS [43–45] and LC × LC‐MS [21,35]. The former, born as an LC miniaturized technique, implies the use of flow rates in the ranges of nL/min, permitted a direct coupling to an electron ionization source without splitting requirements.…”

Free fatty acid profiling in marine algae extract by LC‐MS/MS and isolation as well as quantification of the ω‐3 fatty acid hexadeca‐4,7,10,13‐tetraenoic acid

“…To date, profiling and quantification of Wakame GC-MS is a widely used method for the analysis of fatty acids [14]. However, LC-MS has been rarely used but its importance for fatty acid elucidation is increasing [15][16][17][18][19][20][21]. Typically, these methods use a targeted multiple reaction monitoring (MRM) approach [22].…”

An overview to nano‐scale analytical techniques: Nano‐liquid chromatography and capillary electrochromatography

“…Recently electron ionization (EI) MS was studied with capillary chromatography (CLC) especially for the analysis of neutral compounds . This type of ionization seems to be very promising and could be used instead of atmospheric pressure chemical ionization (APCI) that require high flow rates and therefore cannot be used in nano‐LC.…”

“…Among them, C 18 , C 8 , CN, phenyl‐hexyl, vancomycin, teicoplanin or cyclodextrin silica bonded or amylose‐, cellulose derivatives adsorbed etc. were employed . As in HPLC, in nano‐LC type and size of particles were studied with the aim to obtain better results concerning separation efficiency, resolution and short analysis time.…”