Molecular weight distributions of fulvic acid from the Suwannee River, Georgia, were investigated by electrospray ionization/quadrupole mass spectrometry (ESI/ QMS), and fragmentation pathways of specific fulvic acid masses were investigated by electrospray ionization/ion trap multistage tandem mass spectrometry (ESI/MST/ MS). ESI/QMS studies of the free acid form of low molecular weight poly(carboxylic acid) standards in 75% methanol/25% water mobile phase found that negative ion detection gave the optimum generation of 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 molecule is dependent on the distance between charges. ESI/MST/MS of model compounds 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 specific structures that can serve as a basis for future structural confirmation after these hypothesized structures are synthesized.
Analysis of p,p‘-DDT in environmental samples
requires
monitoring the GC-derived breakdown of this insecticide,
which produces p,p‘-DDD and/or p,p‘-DDE, both
also
primary environmental degradation products. A
performance
evaluation standard (PES) containing p,p‘-DDT but not
p,p‘-DDD or p,p‘-DDE can be injected at regular
intervals
throughout an analytical sequence to monitor GC
degradation.
Some U.S. EPA methods limit GC breakdown of DDT in
the PES to ≤20%. GC/MS analysis of large-volume
natural
water samples fortified with deuterium- and 13C-labeled
p,p‘-DDT exhibited up to 65% DDT breakdown by the GC inlet.
These matrix-enhanced GC degradation amounts substantially exceeded the <20% breakdown levels indicated
by bracketing injections of the PES containing unlabeled
and labeled DDT. Substantial matrix-enhanced GC
degradation
was not observed during analysis of a limited number of
fractionated bed-sediment extracts containing labeled
DDT. Use of isotopically labeled DDT seems to provide
an
effective tool for monitoring sample-specific DDT
breakdown
during GC/MS analysis. However, analyte co-elutions
render impractical their use in GC/ECD analysis. The
oc
currence of matrix-enhanced GC degradation might have
important implications on data quality and the resultant
interpretations of the environmental degradation of DDT
and other thermolabile contaminants.
29. Concentrations of semi-volatile organic compounds (polycyclic-aromatic hydrocarbons) in aquatic biota, Yakima River basin, Washington, 1989-90 ------Quality Assurance Data Water Column 30A-H. Concentrations of carbamate compounds in replicate and (or) spiked whole-water samples from the following locations, Washington: 30A.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.