Lipids are ubiquitous molecules essential for life that exist with an extreme structural variety that, until recently, we have lacked the technology to fully appreciate. Various advanced mass spectrometry methods have been developed to better elucidate lipid isomers, including ozone-induced dissociation, electron-activated dissociation and ultraviolet photodissociation. Others have employed various chemical reactions to achieve lipid isomer discrimination, including photochemical reactions (e.g. Paternò-Bǜchi), charge-switch derivatisation, and epoxidation. However, many of these methods require specialist instrumentation, instrument modification, or complex chemical reactions that limit the widespread adoption of the technique.
In this work, we sought to develop a method for fatty acid double-bond isomer discrimination that can be coupled with standard liquid chromatography/mass spectrometry workflows. We combined charge-switch derivatisation of hydrolysed fatty acids with epoxidation to separate n7, n9, n10 and n12 isomeric monounsaturated fatty acids by C30 reverse phase chromatography. Collisional activation of isomeric fatty acids produced diagnostic ions for the carbon-carbon double bond position providing additional confidence in isomer identification. We used this method to profile fatty acid isomers in prostate cancer cell lines, which aligned with previously published data. Current applications of this method include study of n-10 fatty acids derived from fatty acid desaturase 2 (FADS2), including specificity of this particular lipid isomer in cancer and expanding cancer types in which alternate FADS2 activity is found. Finally, we also detail the potential for targeting FADS2 to improve taxane-based chemotherapy efficicacy.