Structural elucidation of underivatized gangliosides by electrospray-ionization tandem mass spectrometry (ESIMS/MS)

The structural characterization of intact polysialogangliosides by electrospray-ionization mass spectrometry (ESIMS) and tandem mass spectrometry (MS/MS) is described. The negative-ion ESI mass spectra of gangliosides, such as a tetrasialoganglioside GQ1b, showed molecularly related ions with high sensitivity and accuracy. Collision-induced dissociation (CID) MS/MS provided adequate information to characterize the number and positions of sialic acids. ESIMS and CIDMS/MS techniques were applied successfully also in the positive-ion mode for characterization of intact gangliosides. Two isomeric disialogangliosides, GD1a and GD1b, are distinguishable from one another by CIDMS/MS in both negative- and positive-ion modes. The technique is readily applicable to structural analyses such as determining the positional isomers of glycoconjugates.