On‐target separation of analyte with 3‐aminoquinoline/α‐cyano‐4‐hydroxycinnamic acid liquid matrix for matrix‐assisted laser desorption/ionization mass spectrometry

Abstract

3-Aminoquinoline/α-cyano-4-hydroxycinnamic acid (3AQ/CHCA) is a liquid matrix (LM), which was reported by Kumar et al. in 1996 for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. It is a viscous liquid and has some advantages of durability of ion generation by a self-healing surface and quantitative performance. In this study, we found a novel aspect of 3AQ/CHCA as a MALDI matrix, which converges hydrophilic material into the center of the droplet of analyte-3AQ/CHCA mixture on a MALDI sample target well during the process of evaporation of water derived from analyte solvent. This feature made it possible to separate not only the buffer components, but also the peptides and oligosaccharides from one another within 3AQ/CHCA. The MALDI imaging analyses of the analyte-3AQ/CHCA droplet indicated that the oligosaccharides and the peptides were distributed in the center and in the whole area around the center of 3AQ/CHCA, respectively. This 'on-target separation' effect was also applicable to glycoprotein digests such as ribonuclease B. These features of 3AQ/CHCA liquid matrix eliminate the requirement for pretreatment, and reduce sample handling losses thus resulting in the improvement of throughput and sensitivity.

Detection of the Heterogeneous O-Glycosylation Profile of MT1-MMP Expressed in Cancer Cells by a Simple MALDI-MS Method

“…Peptides of different hydrophilicity can be separated on the liquid matrix 3AQ/CHCA spotted onto a MALDI target plate [19]. The 3AQ/CHCA matrix forms a yellow-colored viscous spot when it is applied to the target plate as illustrated in Fig.…”

“…Therefore, prior separation of glycosylated and nonglycosylated peptides is inevitably required for MS analysis [18]. A recently developed MALDI technique using a liquid matrix 3AQ/CHCA, which is composed of 3-aminoquinoline and α-cyano-4-hydroxycinnamic acid, enabled on-target separation of glycosylated and nonglycosylated peptides based on differences in their hydrophilicity after a droplet of protease digest was applied onto the liquid matrix on a MALDI target plate [19]. This on-target separation method was employed to analyze N -glycosylation of ribonuclease B, which is used as a model glycoprotein.…”

Investigations of Some Liquid Matrixes for Analyte Quantification by MALDI

“…In fact, the first work by Tanaka et al [3] on the laser-induced production of gas-phase ions from biomolecules was made using glycerol as the matrix. Room temperature ionic liquids with very low vapor pressures can be useful homogeneous matrixes for MALDI [20][21][22][23][24][25][26][27][28][29][30], as first demonstrated by Armstrong et al [21]. An ionic liquid is prepared by mixing equal amounts of an acid and a base.…”

“…As long as our interest in such liquid materials lies in their homogeneity, however, it will not matter even if some neutrals remain in the samples. In fact, there were reports that nonstoichiometric mixing of acids and bases often produced liquid matrixes that were useful for MALDI [22][23][24][25]. For example, Palmblad and Cramer [22] reported that the linear dynamic range for a MALDI signal could be improved by using a liquid matrix that was a nonstoichiometric mixture of an acid and a base.…”

“…The acids were CHCA (98%), DHB (98%), and SA (99%). The bases were 3-acetylpyridine (3AP) [23], 3-aminoquinoline (3AQ) [25,26], 2-aminopentane (2AP) [27], aniline [23], N-isopropyl-N-methyl-tert-butylamine (IMTBA) [27], N,Ndiethylaniline (DEA) [9,23], N,N-dimethylaniline (DMA) [23,28], pyridine [29], and tributylamine (TBA) [29]. The papers that reported the use of each base for the preparation of an ionic liquid matrix or just liquid matrix are quoted as references for each base.…”