Sublimation as a method of matrix application for mass spectrometric imaging

Abstract

Common organic matrix-assisted laser desorption/ionization (MALDI) matrices, 2,5-dihydroxybenzoic acid, 3,5-dimethoxy-4-hydroxycinnamic acid, and ␣-cyano-4-hydroxycinnamic acid, were found to undergo sublimation without decomposition under conditions of reduced pressure and elevated temperature. This solid to vapor-phase transition was exploited to apply MALDI matrix onto tissue samples over a broad surface in a solvent-free application for mass spectrometric imaging. Sublimation of matrix produced an even layer of small crystals across the sample plate. The deposition was readily controlled with time, temperature, and pressure settings and was highly reproducible from one sample to the next. Mass spectrometric images acquired from phospholipid standards robotically spotted onto a MALDI plate yielded a more intense, even signal with fewer sodium adducts when matrix was applied by sublimation relative to samples where matrix was deposited by an electrospray technique. MALDI matrix could be readily applied to tissue sections on glass slides and stainless steel MALDI plate inserts as long as good thermal contact was made with the condenser of the sublimation device. Sections of mouse brain were coated with matrix applied by sublimation and were imaged using a Q-q-TOF mass spectrometer to yield mass spectral images of very high quality. Image quality is likely enhanced by several features of this technique including the microcrystalline morphology of the deposited matrix, increased purity of deposited matrix, and evenness of deposition. This inexpensive method was reproducible and eliminated the potential for spreading of analytes arising from solvent deposition during matrix application. (J Am

Comparison between vacuum sublimed matrices and conventional dried droplet preparation in MALDI-TOF mass spectrometry

“…The peptides of the combined calibration mixtures 1 and 2 were dissolved in 20% ACN/0.01% TFA to final concentrations of 125 fmol/ L des-arg 1 -bradykinin, 413 fmol/ L angiotensin I, 163 fmol/ L glu 1 -fibrinopeptide B, 6 fmol/ L neurotensin, 250 fmol/ L ACTH (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), 188 fmol/ L ACTH (18 -39), 375 fmol/ L ACTH , and 438 fmol/ L bovine insulin. The in-solution BSA digest was dissolved in 30% ACN/0.1% TFA to a final concentration of 1 fmol/ L. p-Methoxybenzylpyridinium chloride, which was used for the measurements of the effective temperatures, was dissolved in 20% ACN to final concentrations of 2 and 4 pmol/ L. The initial velocities were measured from 350 fmol bovine insulin as analyte (c ϭ 700 fmol/ L, V ϭ 0.5 L) dissolved in 20% ACN/0.01% TFA; 0.5 L matrix solution (30% ACN/0.1% TFA, c ϭ 45 mM for SA; 70% ACN/0.1% TFA, c ϭ 30 mM for all other matrices) and 0.5 L analyte solution were mixed directly on a polished steel target and air-dried for standard DD preparation.…”

“…Also, electrospray deposition and vacuum deposition were reported to yield homogeneous sample preparations with increased analyte intensities [6 -9]. Matrix deposition by sublimation for MALDI imaging has been reported to yield more intense signals with less alkali adducts compared with the electrospray technique [10]. Additionally, sublimed matrix spots deposited on extremely hydrophobic surfaces described in [11][12][13][14] offer a variety of beneficial properties compared with standard dried droplet (DD) preparations: The main advantage of sublimed matrix spots compared with standard DD preparations are higher analyte sensitivities [14 -17].…”

Development of Laser Desorption Imaging Mass Spectrometry Methods to Investigate the Molecular Composition of Latent Fingermarks

“…Recently, matrix sublimation was demonstrated to be a powerful approach for very homogeneous matrix deposition that allows for the detection and IMS of small molecules and proteins with high sensitivity and high spatial resolution [30][31][32]. In the first approach proposed herein, we provide an alternative to the Bdry-wet^method using sublimation for homogeneous matrix deposition followed by automated solvent spray deposition.…”

Solvent-free matrix dry-coating for MALDI imaging of phospholipids

“…Also, the matrix crystal size and the homogeneity of the coating can vary significantly from operator to operator. Recently, a protocol using sublimation for matrix deposition has been reported [19] that gives a homogeneous coating of matrix essential for obtaining high-resolution phospholipid images from tissue. The sublimation apparatus is relatively simple and is commercially available.…”