Structural features of polyacylated anthocyanins using matrix-assisted laser desorption/ionization and electrospray ionization time-of-flight mass spectrometry.

In our continuing studies to isolate water-soluble vacuolar pigments, we expect to elucidate more structural details using mass spectrometry (MS). Because of its sensitivity, only a small amount of pigment extracted from natural plants is required for MS measurement. Nuclear magnetic resonance is also a useful spectroscopic method for structural determination. In this study, two soft ionization techniques, electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), on time-of-flight (TOF) mass spectrometers, were used to analyze five polyacylated anthocyanins with more than two aromatic acid molecules in the side chains. ESI is advantageous for the detection of individual molecular ions, while MALDI is essential for the detection of characteristic fragment ions originating from the anthocyanidin. Although 2,5-dihydroxybenzoic acid (DHBA) is an effective matrix in MALDI-TOFMS to obtain informative fragment ions of polyacylated anthocyanins, α-cyano-4-hydroxycinnamic acid (CHCA) is the preferred matrix for the identification of aglycones. In particular, in measurements of polyacylated anthocyanins with two acylated glycoside chains, fragment ions originating from anthocyanidin can only be observed in MALDI-TOFMS using CHCA as the matrix.

Kasai HF ，Saito N ，Honda T 《-》

Rapid screening of anthocyanins in berry samples by surfactant-mediated matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Surfactant-mediated matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has been used for the identification of flavonoids from three berry extracts: lowbush blueberry (Vaccinium angustifolium), lingonberry (Vaccinium vitis-idaea), and blackberry (Rubus armeniacus). The addition of the surfactant led to suppression of matrix ions from both alpha-cyano-4-hydroxycinnamic acid (CHCA) and 2',4',6'-trihydroxyacetophenone (THAP). This is the first case of this method being successfully employed with a matrix other than CHCA. It was observed that CHCA led to a great deal of fragmentation of the sugar moiety from glycosides, whereas THAP produced more intact glycoside molecules, and thus leads to better characterization of the flavonoids in a berry sample. The flavonoids were characterized and quantified by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) with UV detection. Although MALDI-TOF-MS did not lead to the identification of as many flavonoids, it did enable us to identify many anthocyanin glycosides. Quantification was achieved and demonstrated that use of the THAP matrix can enable quantification of the intact glycosides with relative standard deviation (RSD) values of less than 10% with surfactant addition. These results are comparable with LC results. MALDI-TOF-MS with THAP matrix thus provided a rapid method for the qualitative screening of these compounds. It took only a few minutes, greatly reducing the analysis time from that in traditional LC/MS methods.

Grant DC ，Helleur RJ 《RAPID COMMUNICATIONS IN MASS SPECTROMETRY》

Characterization of humic substances by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and laser desorption/ionization (LDI-)TOFMS have been used to characterize Suwannee River humic substances, obtained from the International Humic Substances Society (IHSS), and Armadale soil fulvic acid (ASFA). An array of MALDI matrices were tested for use with humic substances, including alpha-cyano-4-hydroxycinammic acid (CHCA), 2-(4-hydroxyphenylazo)benzoic acid (HABA), 2,5-dihydroxybenzoic acid (DHBA), sinapinic acid, dithranol and norharmane. DHBA yielded the best results, exhibiting superior ionization efficiency, low noise, broad applicability to the analytes of interest, and most importantly producing an abundance of high mass ions, the highest observed being m/z 1848. A number of sample preparation modes were investigated; the overlayer method improved sample/matrix homogeneity and hence shot-to-shot reproducibility. The choice of the matrix, mass ratio of analyte to matrix, and the sample preparation protocol, were found to be the most critical factors governing the quality of the mass spectra. Matrix suppression was greatly enhanced by ensuring good mixing of matrix and analyte in the solid phase, proper optimization of the matrix/analyte ratio, and optimizing delayed extraction to ensure complete matrix-analyte reaction in the plume before ions are moved to the flight tube. A number of common features, in particular specific ions which could not be attributed to the matrices or to contaminants, were present in the spectra of all the humic substances, regardless of origin or operational definition. Additionally, a prominent repeating pattern of peaks separated by 55, 114 and 169 Da was clearly observed in both LDI and MALDI, suggesting that the humic compounds studied here may have quasi-polymeric or oligomeric features.

Mugo SM ，Bottaro CS 《RAPID COMMUNICATIONS IN MASS SPECTROMETRY》

Structural characterization of synthetic poly(ester amide) from sebacic acid and 4-amino-1-butanol by matrix-assisted laser desorption ionization time-of-flight/time-of-flight tandem mass spectrometry.

Rizzarelli P ，Puglisi C 《RAPID COMMUNICATIONS IN MASS SPECTROMETRY》

Negative and positive ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and positive ion nano-electrospray ionization quadrupole ion trap mass spectrometry of peptidoglycan fragments isolated from various Bacillus species.

Bacher G ，Körner R ，Atrih A ，Foster SJ ，Roepstorff P ，Allmaier G ... -  《JOURNAL OF MASS SPECTROMETRY》