The MALDI-TOF of Grape Procyanidins

The LC/MS does not allow separation and identification of oligomers higher than pentamers because the number of diastereoisomers is large and their separation is not possible. By having positive-ion MALDI-TOF in the reflectron mode, determination of (+)-catechin, (-)-epicatechin oligomers, and their galloylated derivatives up to a heptamer in grape seed extracts as sodium adducts [M+Na]+ is possible 

TABLE 6.20. Molecular and Fragment Ions of the Flavanol-Anthocyanin-Anthocyanin (F-A-A+) Trimers Identified in Tempranillo Aged Wines2 

TABLE 6.21. Masses Observed by MALDI-TOF and those Calculated by the Equation 290 + 288c + 152 + 23  

Polymer Ester [M+Na]+ Positive Linear Positive Reflectron 

The dry grape seed extract is dissolved in acetone or methanol at 2mg/mL, a 2,5-dihydroxybenzoic (DHB) acid matrix is prepared in tetrahydrofuran (THF) at 20mg/mL, and the sample and matrix solutions are mixed at a 1 1 (v/v) ratio. Sodium apparently arises from the seeds themselves and only a minute amount of sodium is needed. The use of DHB and water-free solvents, such as anhydrous THF, acetone, or methanol for the sample and matrix preparation was reported to lead to the best analytical conditions in reflectron mode, providing the broadest mass range with the least background noise (Yang and Chien, 2000). 

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