Assignment of acetyl groups to O‐2 and/or O‐3 of pectic oligogalacturonides using negative electrospray ionization ion trap mass spectrometry

Abstract

Partially acetylated and methylated oligogalacturonides produced by enzymatic hydrolysis of sugar beet pectin were analysed by negative electrospray ionization ion trap mass spectrometry (ESI‐ITMS). The ¹⁸O labelling of the oligomer reducing end allowed the precise assignment of the fragments resulting from glycosidic bond and cross‐ring cleavages. The collisional‐induced dissociation of the C_i and Z_j fragment ions through sequential MSⁿ experiments always displayed ^{0, 2}A‐type cross‐ring cleavage ions which were related to C₂H₄O₂ losses. These ^{0, 2}A ions appeared to be highly diagnostic ions allowing the precise location of the acetyl groups to the O‐2 and/or O‐3 of the acetylated galacturonic acid residues. Copyright © 2003 John Wiley & Sons, Ltd.