MALDI post-source decay and LIFT-TOF/TOF investigation of α-cyano-4-hydroxycinnamic acid cluster interferences

Abstract

Large signals from ␣-cyano-4-hydroxycinnamic acid (CHCA) matrix complexes with sodium and potassium ions were found to interfere with sensitive matrix-assisted laser desorption/ ionization (MALDI) analysis of a hydrochloric acid digest of gelatine preparations. The nature of some selected matrix clusters was investigated by conventional post-source decay and LIFT-TOF/TOF experiments. The matrix clusters fragmented readily by neutral evaporation to give smaller sized matrix cluster species without matrix disintegration. Their characterization distinguished them from peptide signals, in particular from those that had the same nominal mass and differed only in the fractional part of the mass as encountered for gelatine-derived peptides. Knowledge of the molecular composition of these cluster species allowed using them for internal calibration of the MALDI mass spectra. The hydrolytic peptides could be analyzed with increased sensitivity when using 2,5-dihydroxy benzoic acid (DHB) as the MALDI matrix. (J Am Soc Mass Spectrom 2004, 15, 336 -343)

Interferences and contaminants encountered in modern mass spectrometry

“…The obvious means to decrease occurrence and interference of matrix clusters is the avoidance or minimization of salt contaminations of the matrix and the sample which can be achieved by on-target washing of sample/matrix spots [65,71,72], sample purification before sample/matrix deposition [73,74], or a combination of both approaches. Neubert et al employed post source decay MS/MS analysis to distinguish matrix clusters from peptide signals [67], Smirnov et al utilized washing steps with diammonium citrate buffer to eliminate or reduce 4-HCCA matrix clusters [66], and Kim et al added nitrilotriacetic acid to sample/matrix preparation and achieved matrix cluster suppression and peptide signal enhancement [68].…”

“…-dihydroxybenzoic acid (DHB)[29,34,42,[65][66][67][68].Keller and Li established the following algorithm on the composition of matrix clusters from 4-HCCA and DHB as agglomerates of matrix molecules and alkali ions, typically sodium and potassium[69]:M Cluster = nM − xH + yK + zNa, x = y + z − 1 and y + z = n + 1 or x = nThis algorithm allows the prediction of m/z values at which matrix clusters can potentially appear. For example, in the case of the commonly employed matrix substance 4-HCCA, matrix clusters typically appear in bundles containing ∼3-7 specific signals within a bundle.…”

Infrared Laser Ablation Sample Transfer for MALDI and Electrospray

“…MALDI mass spectra were obtained in reflectron mode and were the sum of 500 UV laser shots. Figure 2a, the large peaks (indicated with asterisks) in the low mass region of the mass spectrum correspond to matrix, matrix cluster, and matrix fragment ions typical for this matrix [30][31][32]. At 180 IR laser shots, the protonated angiotensin II ion is the most intense peak and, at 300 shots, the protonated molecule peak is the most intense peak with only a few other less intense peaks in the mass spectrum.…”

Direct identification of Monilinia brown rot fungi on infected fruits by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

“…Monoisotopic masses m/z = 4373.3 and m/z = 4442.0 were selected for fragmentation. MALDI-TOF/TOF tandem mass spectrometry was performed using the LIFT technology [26] over a m/z range of 20-4500 in the positive ion mode. The MALDI target plate was prepared by pipetting 0.7 µl of eluted ziptip protein samples onto the target spots, which were overlaid with 0.7 µl matrix [HCCA (Bruker Daltonics GmbH), 2 mg/ml in acid (TFA) (50:49.9:0.1)].…”