This article is available online at http://www.jlr.org ing in cell membranes. Specifi c functions and variations of the various phospholipids (PL), the most abundant lipids in eukaryotic cell membranes, are, however, still poorly understood ( 1 ). A diversity of PL in a fi nely balanced equilibrium is used by cells to construct stable and functional membranes, and PL composition determines most of the physico-chemical cell membrane properties such as fl uidity, permeability and thermal phase behavior ( 2 ).Knowledge of the function of lipids within the cell has benefi ted from the development of increasingly sensitive and selective analytical techniques, particularly those based on mass spectrometry ( 3, 4 ). Among these techniques, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) ( 5 ) has been very successful in studies of the compositions of lipids and other crucial biological molecules. MALDI-MS has allowed direct analysis of complex and unfractionated samples, such as the study of peptide profi les below the level of a single cell ( 6 ). In lipidomics, MALDI-MS has provided fast and simple acquisition of mass spectra with lipid profi les of cells, tissues and body fl uids ( 7 ).MALDI-MS lipid fi ngerprinting can, for example, help studies aimed at understanding the effect of membrane lipid composition on cell membrane behavior after temperature changes. This knowledge is essential for cryopreservation studies of a variety of cells, including oocytes The double molecular layer of polar lipids is a marvelous architectural feature of exquisite biological engineerThis work was supported by the Brazilian research foundations FAPESP (Grant 2008/10756-7) and CNPq.

Amazonian oils and fats display unique triacylglycerol (TAG) profiles and, because of their economic importance as renewable raw materials and use by the cosmetic and food industries, are often subject to adulteration and forgery. Representative samples of these oils (andiroba, Brazil nut, buriti, and passion fruit) and fats (cupuaçu, murumuru, and ucuúba) were characterized without pre-separation or derivatization via dry (solvent-free) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Characteristic profiles of TAG were obtained for each oil and fat. Dry MALDI-TOF MS provides typification and direct and detailed information, via TAG profiles, of their variable combinations of fatty acids. A database from spectra could be developed and may be used for their fast and reliable typification, application screening, and quality control.

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Direct infusion electrospray ionization mass spectrometry (ESI-MS) of aqueous/methanolic extracts of biodiesel samples is shown to permit simple and fast fingerprinting typification, identification of the alcohol used in the trans-esterification process, monitoring of degradation and adulteration, and screening of residual glycerin and mono-, di-, and tri-glycerides. As proof-of-principle cases, ESI-MS fingerprints in both the positive and the negative ion modes were acquired for biodiesel samples derived from soybean oil, sunflower oil, canola oil, olive oil, castor oil, jatropha curcas oil, palm oil, lard, and tallow. In the negative ion mode, characteristic sets of ions corresponding to de-protonated fatty acids were detected for each type of biodiesel, thus allowing their reliable typification via these taxonomic markers. Biodiesel degradation was also monitored by ESI(-)-MS with the detection of degradation markers, mainly oxidized fatty acids. When using ESI(+)-MS, the main diagnostic ions detected were the protonated fatty esters, which reveal therefore both the oil source and the alcohol (methanol or ethanol, or other heavier alcohols) used for trans-esterification. Residual glycerin and mono-, di-, and tri-glycerides are also detected, which makes ESI-MS also applicable for laboratory and on-site screening of biodiesel quality.