Rapid Fatty Acid Profiles from Glyceride Fragments using MALDI MS

Abstract: A Matrix Assisted Laser Desorption Ionization (MALDI) mass spectrometer is commonly used to identify triglycerides (TAG) and diglycerides (DAG) in oils. However, distinguishing diglycerides from “DAG-like fragments” produced when using a matrix like DHB can complicate analyses. Efforts have been made to eliminate these fragments by creating an alkaline environment to remove free protons or placing the samples on a layer of nitrocellulose. Contrary to the approach of suppressing these peaks, these fragments can be useful for analysis. The fragment peaks are more prevalent than DAG peaks and quantitatively represent the fatty acid distribution. Rather than attempting to decipher the intensities of overlapping triglyceride peaks, using the DAG fragment peaks simplifies the task. These peaks result from the combined fragmentation of diglycerides and triglycerides into protonated molecules, each containing two fatty acids.

In an exemplary study, one microgram oil samples were applied to each cell of the MALDI plate with the matrix 4-Chloro-α-cyanocinnamic acid (ClCCA) in 80% acetonitrile with 0.1% trifluoroacetic acid. The data obtained from the MALDI spectra of individual samples was sufficient to deduce the ratio of fatty acids present in the glycerides. The results of this method compare favorably with gas chromatograph (GC) analysis of fatty acid methyl esters (FAME) prepared from TAG rich oils. Due to the simplicity and speed of MALDI preparation and analysis, this method can significantly increase the rate at which glycerides can be analyzed when compared with current "fast GC" methods. This method correlates significantly with FAME analysis by GC.