While maintaining anatomical integrity, matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) has allowed researchers to directly probe tissue, map the distribution of analytes and elucidate molecular structure with minimal preparation. MALDI-ion mobility (IM)-orthogonal time-of-flight mass spectrometry (oTOFMS) provides an advantage by initially separating different classes of biomolecules such as lipids, peptides, and nucleotides by their IM drift times prior to mass analysis. In the present work the distribution of phosphatidlycholine and cerebroside species was mapped from 16 μm thick coronal rat brain sections using MALDI-IMoTOFMS. Furthermore, the use of gold nanoparticles as a matrix enables detection of cerebrosides, which although highly concentrated in brain tissue, are not easily observed as positive ions because of intense signals from lipids such as phosphatidlycholines and sphingomyelins.

Combining© matrix-assisted© laser© desorption/ionization© (MALDI)© mass© spectrometry© with© ion mobility© (IM)© results© in© the© fast© sorting© of© biomolecules© in© complex© mixtures© along© trend© lines. In© this© two-dimensional© (2D)© analysis© of© biological© families,© lipids,© peptides,© and© nucleotides are© separated© from© each© other© by© differences© in© their© ion© mobility© drift© times© in© a© timescale© of hundreds© of© microseconds.© Molecular© ions© of© similar© chemical© type© fall© along© trend© lines© when plotted© in© 2D© plots© of© ion© mobility© drift© time© as© a© function© of© m/z.© In© this© study,© MALDI-IM© MS is©used©to©analyze©species©from©all©of©the©major©phospholipid©classes.©Complex©samples, including© tissue© extracts© and© sections,© were© probed© to© demonstrate© the© effects© that© radyl© chain length,© degree© of© unsaturation,© and© class/head© group© have© upon© an© ion's© cross© section© in© the gas© phase.© We© illustrate© how© these© changes© can© be© used© to© identify© individual© lipid© species© in complex© mixtures,© as© well© as© the© effects© of© cationization© on© ion© cross© section© and© ionization efficiency

Comprehensive metabolome analysis using mass spectrometry (MS) often results in a complex mass spectrum and difficult data analysis resulting from the signals of numerous small molecules in the metabolome. In addition, mass spectrometry alone has difficulty measuring isobars and chiral, conformational, and structural isomers. When a matrix assisted laser desorption ionization source (MALDI) is added, the difficulty and complexity are further increased. Signal interference between analyte signals and matrix ion signals produced by MALDI in the low mass region (<1500 Da) cause detection and or identification of metabolites difficult by mass spectrometry alone.However, ion mobility spectrometry (IMS) coupled with MS (IM-MS) provides a rapid analytical tool for measuring subtle structural differences in chemicals. IMS separates gas phase ions based on their size-to-charge ratio. This study, for the first time, reports the application of MALDI to the measurement of small molecules in a biological matrix by Ion Mobility-Time of Flight Mass Spectrometry (IM-TOFMS) and demonstrates the advantage of ion-signal dispersion in the second dimension. Qualitative comparisons between metabolic profiling of the Escherichia coli metabolome by MALDI-TOFMS, MALDI-IM-TOFMS, and ESI-IM-TOFMS (electrospray ionization) are reported. Results demonstrate that mobility separation prior to mass analysis increases peak-capacity through added dimensionality in measurement. Mobility separation also allows detection of metabolites in the matrix-ion dominated low-mass range (m/z < 1500 Da) by separating matrix-signals from non-matrix signals in mobility space.

Ethanol is used in a variety of topical products. It is known to enhance the permeability of the skin by altering the ability of the stratum corneum (SC) intercellular membranes to form an effective barrier. In addition, ethanol and other alcohols are key components of antiseptic gels currently used for hand wash. Using infrared and deuterium NMR spectroscopy as well as calorimetry, we have investigated the effect of ethanol on a model membrane composed of lipids representing the three classes of SC lipids, an equimolar mixture of N-palmitoylsphingosine (ceramide), palmitic acid and cholesterol. Ethanol is found to influence the membrane in a dose dependent manner, disrupting packing and increasing lipid motion at low concentrations and selectively extracting lipids at moderate concentrations.

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