Molecular resolution and fragmentation of fulvic acid by electrospray ionization/multistage tandem mass spectrometry

Molecular weight distributions of fulvic acid from the Suwannee River, Geor gia, were investigated by electrospray ionization/quadrupole mass spectrome try (ESI/ QMS), and fragmentation pathways of specific fulvic acid masses w ere investigated by electrospray ionization/ion trap multistage tandem mass spectrometry (EST/MST/ MS). ESI/QMS studies of the free acid form of low m olecular weight poly(carboxylic acid) standards in 75% methanol/25% water m obile phase found that negative ion detection gave the optimum generation o f parent ions that can be used for molecular weight determinations. However , experiments with poly(acrylic acid) mixtures and specific high molecular weight standards found multiply charged negative ions that gave a low bias to molecular mass distributions. The number of negative charges on a molecu le is dependent on the distance between charges. ESI/MST/MS of model compou nds found characteristic water loss from alcohol dehydration and anhydride formation, as well as CO2 loss from decarboxylation, and CO loss from ester structures. Application of these fragmentation pathways to specific masses of fulvic acid isolated and fragmented by ESI/MST/MS is indicative of spec ific structures that can serve as a basis for future structural confirmatio n after these hypothesized structures are synthesized.