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

Abstract

The properties of several cinnamic acid compounds used as matrices for matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were investigated as standard dried droplet (DD) and vacuum sublimed preparations. The differences between both preparation methods were analyzed with regard to matrix grain size, internal ion energy, initial velocity, analyte intensity, and analyte incorporation depth. Some of the used cinnamic acid derivatives exhibit clearly reduced grain sizes as sublimed preparations compared with standard DD approaches. In these cases higher effective temperatures could be measured accompanied by increased analyte intensities, which can be explained by stronger volatilization processes caused by a hindered heat dissipation resulting in a raised analyte transfer into the gas phase. For all sublimed compounds, a strong increase of the initial ion velocity compared with DD preparations could be measured. Higher initial ion velocities correlate with a decrease in internal ion energy which might be attributed to the very uniform crystal morphology exhibited by sublimed compounds. For sublimed matrices without reduced grain size, at least slightly higher analyte intensities could be detected at raised laser fluences. Analyte accumulation in the uppermost matrix layers or the detected higher ion stability can be explanations for these results. Ever increasing numbers of samples call for automation in high-throughput workflows. One of the key areas for progress in automated MALDI analyses consists of improved sample preparation techniques. Numerous efforts have been conducted for improving the preparation step, e.g., the generation of thin uniform matrix layers with high shot-to-shot reproducibility using the aerospray technique by combination of matrix and nitrocellulose [4] or for analysis of synthetic polymers [5]. 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]. This is likely related to the formation of considerably smaller crystals and narrow size distribution of thin-film sublimed matrices, such as ␣-cyano-4-hydroxycinnamic acid (CHCA), compared with DD preparations with comparatively large particle sizes and broader size distribution [15]. As a consequence of this, the specific matrix surface area as well as the amount of potential binding places increases compared with standard DD precipitates, which will result in increased analyte binding properties. Additionally, th...

Thin-Layer Matrix Sublimation with Vapor-Sorption Induced Co-Crystallization for Sensitive and Reproducible SAMDI-TOF MS Analysis of Protein Biosensors

“…DD leads to non-uniform analyte/matrix co-crystallization forming "sweet spots" which reduce inter-and intra-assay reproducibility [14][15][16]. Alternative matrix deposition methods have been reported to enhance homogeneity of matrix/analyte co-crystals [17][18][19][20][21][22][23][24][25][26][27][28], although MALDI-TOF measurements typically yield precisions above 20 % relative standard deviation (RSD). Performing relative quantitation against an internal standard at similar molecular mass to the target analyte improves MALDI precision to G10 % RSD [29,30].…”

Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Mechanistic Studies and Methods for Improving the Structural Identification of Carbohydrates

“…Over the last three decades, fundamental ionization mechanisms have been systematically studied by manipulating one or more parameters among di erent matrix systems. 22,35) E ects of the incorporation of analytes into matrix solid, [36][37][38][39][40] matrix-to-analyte ratio, 41,42) solvent constituents, [43][44][45][46][47] laser excitation conditions, 22,48,49) and the crystal morphology of samples 47,[50][51][52][53][54][55] on ion production were investigated. A prerequisite of successful MALDI processes is absorption of laser energy by matrices.…”

“…22,80) Results of these studies suggest that factors a ecting the desorption e ciency can be classi ed into two categories: excitation parameters 36,[81][82][83][84][85][86] and intrinsic properties of samples. 51,[87][88][89][90][91][92] Generally, desorption e ciency increases when MALDI crystal size decreases 51) and the system temperature increases. [87][88][89][90][91][92] On the basis of factors in uencing desorption e ciency, mathematical equations as well as computational methods, such as molecular dynamics (MD) simulations, have been used to quantitatively describe the desorption process.…”

An Evaluation Of Direct Identification Of Pathogens From Blood Cultures By Maldi-Tof Mass Spectrometry

“…Lina Savickaitė, Jelena Kopeykinienė Klaipeda University Hospital, Lithuania sample preparation, matrix solutions and organic solvents, affect the quality and reproducibility of bacterial MALDI-TOF mass spectrometry fingerprints (11)(12)(13)(14)(15)(16). With a special set of MALDI Sepsityper is possible to identify bacteria directly from the positive blood culture (17)(18)(19)(20)(21)(22)(23)(24)(25).…”