Identification of diacylglycerols and triacylglycerols in a structured lipid sample by atmospheric pressure chemical ionization liquid chromatography/mass spectrometry

Abstract

Atmospheric pressure chemical ionization liquid chromatography/mass spectrometry was used in the identification of diacylglycerol and triacylglycerol (TAG) molecular species in a sample of a structured lipid. In the study of acylglycerol standards, the most distinctive differences between the diacylglycerol and TAG molecules were found to be the molecular ion and the relative intensity of monoacylglycerol fragment ions. All saturated TAG ranging from tricaproin to tristearin, and unsaturated TAG including triolein, trilinolein, and trilinolenin, had ammonium adduct molecular ions [M + NH 4 ] + . Protonated molecular ions were also produced for TAG containing unsaturated fatty acids and the intensity increased with increasing unsaturation. Diacylglycerol fragment ions were also formed for TAG. The ammonium adduct molecular ion was the base peak for TAG containing polyunsaturated fatty acids, whereas the diacylglycerol fragment ion was the base peak for TAG containing saturated and monounsaturated medium-and long-chain fatty acids; the relative intensities of the ammonium adduct molecular ions were between 14 and 58%. The most abundant ion for diacylglycerols, however, was the molecular ion [M − 17] + , and the relative intensity of the monoacylglycerol fragment ion was also higher than that for TAG. These distinctive differences between the diacylglycerol and TAG spectra were utilized for rapid identification of the acylglycerols in the sample of a structured lipid.Lipase-catalyzed interesterification has been used in lipid modification for the production of different kinds of lipids according to specific requirements, for instance the enrichment of triacylglycerols (TAG) with polyunsaturated fatty acids, especially essential fatty acids (1,2), and the incorporation of medium-or short-chain fatty acids into TAG (3-5). Since the interesterification alters the fatty acid composition and distribution in the acylglycerols, a group of new TAG is produced in the interesterification. Diacylglycerols are formed as the intermediates and are also found in the interesterified products; the level of diacylglycerols varied in different interesterification processes or under different reaction parameters (6,7).Reversed-phase-high-performance liquid chromatography (RP-HPLC) is a practical method for the separation of TAG molecular species according to the differences in carbon numbers and unsaturation levels of fatty acids in TAG (8-12). Equivalent carbon number (ECN) or partition number, a summary of both the carbon number and the degree of unsaturation of fatty acids, is commonly used for the tentative identification of TAG (8)(9)(10)13,14). However, it was difficult to distinguish diacylglycerols from TAG on the RP-HPLC using the ECN. Even though it is possible to separate and identify the diacylglycerol and TAG molecular species by thin-layer chromatography followed by HPLC fractionation and analysis using gas-liquid chromatography (9), the procedure is tedious and seldom used.Mass spectrometry (MS) is a sensitive method for...

Analytical strategies for discriminating archeological fatty substances from animal origin

“…These methods are of particular value to study animal fats that are composed of high molecular weight compounds such as DAGs, and TAGs (Gresti et al, 1993;Byrdwell & Emken, 1995;Laakso, 1996;Mottram & Evershed, 1996;Mu, Sillen, & Hoy, 2000;Byrdwell, 2001;Han & Gross, 2001;Hvattum, 2001;Andrikopoulos, 2002;Laakso, 2002;Burchgraber, Ulberth, & Anklam, 2004;Momchilova et al, 2004;McAnoy, Wu, & Murphy, 2005;Leskinen, Suomela, & Kallio, 2007;Molkentin, 2007;Picariello, Sacchi, & Addeo, 2007). Nevertheless, few reports have focused on the use of electrospray (ESI) and atmospheric pressure chemical ionization (APCI) to unravel the molecular compositions of fatty substances of animal origin preserved in the archeological record (Kimpe, Jacobs, & Maelkens, 2001Evershed et al, 2002;Kimpe et al, 2004;Mirabaud, 2007;Mirabaud, Rolando, & Regert, 2007;Romanus et al, 2007).…”

“…The approach adopted was based on earlier studies of modern fats and oils with the same methodology (Mottram, Woodbury, & Evershed, 1997;Mu, Sillen, & Hoy, 2000). Although initially investigating olive oil residues, it was further exploited to detect animal fats to specify their origin (Kimpe, Jacobs, & Waelkens, 2002;Kimpe et al, 2004).…”

“…Mass spectra of TAG species are characterized by intense [M þ H] þ and DAG fragment ions [MH-RCOOH] þ ions (Mottram & Evershed, 1996;Mottram, Woodbury, & Evershed, 1997;Mu, Sillen, & Hoy, 2000;Kimpe, Jacobs, & Waelkens, 2001;Laakso, 2002). Interestingly, the fatty acyl moieties in the sn-1 and sn-3 positions give rise to more abundant [M-RCOO] þ ions than those that are in the sn-2 position; the loss of a [M-RCOO] þ ion in the sn-2 position is indeed energetically less favorable than that in the sn-1 or sn-3 position (Mottram & Evershed, 1996).…”

Chemometric approaches in calibration experiments of trilinolenoylglycerol by liquid chromatography ion-trap mass spectrometry

“…At 12 l/min the increasing of the internal energy is more dramatic and all the precursor ions are over the threshold of fragmentation; therefore, the formation of the FFA dominates. It is important to mention that fragmentation of TALG has been observed by using atmospheric pressure chemical ionization [2] and tandem sector MS [3] but in any of these works the FFA ammoniated adduct was observed. The fragmentation of TALG into FFA as a result of varying the drying gas flow in ESI-MS experiments, to our knowledge, has not been previously reported.…”

“…A s an essential polyunsaturated fatty acid, ␣-linoleic acid (ALA, 18:3n-3) is not synthesized de novo in animals, but must be provided in their diets in the form of triacylglycerol [1]. The development of analytical methods in the analysis and quantification of ALA and more general triacylglycerols (TAG) is of considerable importance [2,3] in view of their involvement in many vital biochemical processes and their association with the alleviation of a wide variety of diseases [4,5]. Quantification of TAG using coupled techniques such as LCMS depends mainly on two aspects, the sample preparation technique and the instrumental condition settings.…”