title: Analysis of free fatty acids by ultraviolet laser desorption ionization mass spectrometry using insect wings as hydrophobic sample substrates.
abstract: Physiologically relevant free fatty acids (FFAs) were analyzed by UV-laser desorption/ionization orthogonal extracting time-of-flight mass spectrometry (LDI-oTOF-MS). Dissected wings from Drosophila melanogaster fruit flies were used as the hydrophobic, laser energy strongly absorbing sample substrates. Using untreated substrates produces predominantly molecular [M + K](+) ions of the FFAs, whereas other alkali metal adducts can be generated by treating the wings with the corresponding alkali hydroxide before spotting of analyte. Limits of detection for the positive ion mode were determined for mixtures of isolated FFAs to values in the low 10 pmol range. Specific values depend on chain length and degree of unsaturation. R(2) coefficients for the analysis of saturated FFAs were found to be generally close to 0.98 over about 3 orders of magnitude if an internal standard (15:0 FFA) was added. Semiquantitative analyses of mixtures containing unsaturated FFAs are also possible but require more effort on the calibration strategy. Notably, both saturated and (poly-)unsaturated FFAs are detected sensitively in the presence of relatively high concentrations of other physiologically abundant lipids (phospholipids and triacyclglycerols). This simplifies screening of the FFA composition in crude tissue extracts. This feature is demonstrated by the analysis of a crude liver extract and that of fingermarks.
authors.affiliation: Institute for Hygiene, University of Münster , Robert-Koch-Straße 41, 48149 Münster, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Pirkl
authors.forename: Martin
authors.initials: M
authors.lastname: Meier
authors.forename: Yulia
authors.initials: Y
authors.lastname: Popkova
authors.forename: Matthias
authors.initials: M
authors.lastname: Letzel
authors.forename: Andreas
authors.initials: A
authors.lastname: Schnapp
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schiller
authors.forename: Klaus
authors.initials: K
authors.lastname: Dreisewerd
mesh_terms: D000818:Animals; D004331:Drosophila melanogaster; D005230:Fatty Acids, Nonesterified / Q000032:analysis*; D057927:Hydrophobic and Hydrophilic Interactions; D013058:Mass Spectrometry / Q000379:methods*; D051379:Mice; D013056:Spectrophotometry, Ultraviolet; D014921:Wings, Animal / Q000737:chemistry*
chemical_list: D005230:Fatty Acids, Nonesterified