Advancing Stable Isotope Analysis with Orbitrap-MS for Fatty Acid Methyl Esters and Complex Lipid Matrices

Isotopic analysis plays a crucial role in different scientific fields, offering valuable insights that aid in elucidating biosynthetic pathways, determining geographic origin, and identifying product adulteration. Established mass spectrometry techniques for isotopic analysis require the conversion of samples into gases prior to introduction into the systems. Moreover, the ionization process in these methods is destructive, potentially leading to the loss of essential molecular structure information. Thus, alternative analytical methods, such as Orbitrap-MS, could be a useful tool to determine stable isotope ratios. This paper describes an Orbitrap-based method using stearic acid methyl ester as a model molecule to determine the stable isotopic ratios of fatty acids and fatty acid methyl esters (FAMEs) in different vegetable butters. Orbitrap analyses were performed in positive ionization mode with both [M + H]⁺ and [M + Na]⁺ ions considered for the analysis. Nine standards (Std 1-Std 9) and three vegetable butters (cupuaçu, cocoa, and shea) were employed in the study. The standards were employed to develop the method and were measured using HPLC and a dual-inlet system. Both injections achieved high precision (<1.5‰) when compared with the IRMS data; however, the HPLC showed the most accuracy and was selected for direct injection measurement of the natural samples. Our results demonstrated the efficiency of the ESI-Orbitrap system in differentiating sources based on δ¹³C values. This study not only advances the use of high-resolution mass spectrometry for isotope analysis but also opens new avenues for applying stable isotopes in food sciences.