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Factors that affect molecular weight distribution of Suwannee river fulvic acid as determined by electrospray ionization/mass spectrometry

October 11, 2004

Effects of methylation, molar response, multiple charging, solvents, and positive and negative ionization on molecular weight distributions of aquatic fulvic acid were investigated by electrospray ionization/mass spectrometry. After preliminary analysis by positive and negative modes, samples and mixtures of standards were derivatized by methylation to minimize ionization sites and reanalyzed.

Positive ionization was less effective and produced more complex spectra than negative ionization. Ionization in methanol/water produced greater response than in acetonitrile/water. Molar response varied widely for the selected free acid standards when analyzed individually and in a mixture, but after methylation this range decreased. After methylation, the number average molecular weight of the Suwannee River fulvic acid remained the same while the weight average molecular weight decreased. These differences are probably indicative of disaggregation of large aggregated ions during methylation. Since the weight average molecular weight decreased, it is likely that aggregate formation in the fulvic acid was present prior to derivatization, rather than multiple charging in the mass spectra.

Publication Year 2004
Title Factors that affect molecular weight distribution of Suwannee river fulvic acid as determined by electrospray ionization/mass spectrometry
DOI 10.1016/j.aca.2004.06.065
Authors Colleen E. Rostad, Jerry A. Leenheer
Publication Type Article
Publication Subtype Journal Article
Series Title Analytica Chimica Acta
Index ID 70185109
Record Source USGS Publications Warehouse
USGS Organization Denver Federal Center; Toxic Substances Hydrology Program