Localization of Double Bonds in Wax Esters by High-Performance Liquid Chromatography/Atmospheric Pressure Chemical Ionization Mass Spectrometry Utilizing the Fragmentation of Acetonitrile-Related Adducts

Abstract

Unsaturated wax esters (WEs) provided molecular adducts with C(3)H(5)N ([M + 55](+•)) in APCI sources in the presence of acetonitrile. CID MS/MS of [M + 55](+•) yielded fragments allowing the localization of double bond(s) in the hydrocarbon chains of the WEs. These fragments were formed by a cleavage on each side of the double bond. In methylene-interrupted polyunsaturated WEs, diagnostic fragments related to each double bond were detected; the most abundant were those corresponding to the cleavage of the C-C bond next to the first and the last double bond. To differentiate between those fragments differing in their structure or origin, a simple nomenclature based on α and ω ions has been introduced. Fragmentation of the α-type ions (fragments containing an ester bond) provided information on the occurrence of a double bond in the acid or alcohol part of the WEs. While no significant differences between the spectra of the WEs differing by cis/trans isomerism were found, the isomers were separated chromatographically. A data-dependent HPLC/APCI-MS(2) method for the comprehensive characterization of WEs in their complex mixtures has been developed and applied to natural mixtures of WEs isolated from jojoba oil and beeswax. More than 50 WE molecular species were completely identified, including the information on the acid and alcohol chain length and the position of the double bonds.

Analysis of 1,2-diol diesters in vernix caseosa by high-performance liquid chromatography – atmospheric pressure chemical ionization mass spectrometry

“…The full-scan APCI mass spectra showed signals of protonated molecules, partially overlapping with radi- The covalent adducts [M+C 3 H 5 N] +• can be generated by gas-phase reactions in the APCI sources in the presence of acetonitrile, and we have shown that these ions are useful for the localization of double bonds in various lipids [41,43]. The CID fragmentation of m/z 841.8 ([M+C 3 H 5 N] +• of 16:0//18:1n-9/18:1n-9) in the ion trap gave a prominent fragment m/z 728.7 (˛-ion), which can be rationalized by the loss of octane radical, and indicated the n-9 position of the double bond (Fig.…”

“…The parent mass list was calculated for [M+NH 4 ] + ions of all possible 1,2-DDE with the total number of carbons and double bonds in the range of 49-91 and 0-4, respectively. Two additional HPLC runs were used to localize the positions of double bonds using [M+C 3 H 5 N] +• formed in the APCI source [41] under the same separation conditions as described above. In both runs, the MS method consisted of two scan events; the first scan event was the full scan in the 400-1500 m/z range and the second scan was either ion-trap CID of the most intense [M+C 3 H 5 N] +• ion from the parent mass list with the normalized collision energy of 29-33% and isolation with 2 Da or quadrupole HCD of the most intense [M+C 3 H 5 N] +• ion from the parent mass list with the normalized collision energy of 18-21% and isolation with 2 Da.…”

“…4A). The CID spectra also contained satellite fragments resulting from the cleavages of the C C bonds more distant from the site of the double bond (mostly ±14 Da, m/z 714.6 and m/z 742.7) [41,43] spectra were less complicated, showing only ω and ˛ diagnostic fragments accompanied by small satellite ions at +14 Da (Fig. 4B).…”

Structural characterization of wax esters by electron ionization mass spectrometry

“…GC coupled with electron ionization mass spectrometry (GC/EI-MS) offers high separation effi ciency, ease of use, and mass spectra allowing structure elucidation. Other analytical methods based on liquid chromatography/mass spectrometry or matrix-assisted laser desorption/ionization mass spectrometry (13)(14)(15) can also be utilized, especially in the case of thermally unstable or insuffi ciently volatile WEs.…”

Rapid Identification and Quantification of Linear Olefin Isomers by Online Ozonolysis-Single Photon Ionization Time-of-Flight Mass Spectrometry

“…Recently, the technical advances in mass spectrometry (MS) [8], especially new ionization methods such as matrix-assisted laser desorption/ ionization (MALDI) [9] and electrospray ionization (ESI) [10], and multistage MS [11][12][13] have become powerful tools in overcoming the above mentioned difficulties. In addition, a variety of chemical derivatizations in conjunction with MS have also become effective methods for analysis of compounds with different double bond positions from following processes, such as dimethyl sulfide addition reaction (DSAR) [14], crossmetathesis (CM) [15,16], charge-switch derivatization (CSD) [17], and covalent adduct chemical ionization (CACI) [18,19].…”