Alexandra C. Stenson
- B.S. Florida State University, Chemistry and Environmental Chemistry, 1998
- Ph.D. Florida State University, Analytical Chemistry, 2002
Characterization of unknown compounds from extremely complex mixtures remains one of the major challenges in modern analytical chemistry. Complex mixtures in themselves are not necessarily crippling if enough is known about the components allowing for the design of highly specific separation techniques (this is generally taken advantage of for biological samples). True unknowns are somewhat more difficult, but can generally be structurally identified as long as enough information-rich data are compiled (e.g. NMR, IR, X-ray crystallography and mass spectra). The combination of complexity and true unknowns is, however, still a large stumbling block.
Mixtures too complex to be fractionated into individual components are relatively common in nature. Humic substances (the condensation and degradation products of dead and decaying plant and animal matter) are one such example. Humics are ubiquitous in nature and of great agricultural and environmental importance. More recently biomedical uses for these compounds (particularly as antiviral agents) have also been identified.
In this research group we are using chromatography and mass spectrometry to characterize humic substances on the molecular level. Research goals involve the development of pre-fractionation methods that reduce the overall complexity of humic mixtures; identification of structural components for individual humic molecules through tandem MS techniques; and mimicking of humic substances through synthetic standardsSee More
Chromatographic Pre-fractionation of Suwannee River
Fulvic Acid: a) Isobaric complexity is reduced in early and late eluting fractions, b & c) compositional differences between fractions are evident; as expected, early eluting material is more polar (i.e. more oxidized as indicated by higher O/C rations and KMDs).
Compositional Differences between Suwannee River
Fulvic Acid Fractions: Summarized are MS2 and H/D exchange data. Together, they indicate that early eluting fractions have a high carboxylic acid content while late eluting fractions have a higher alcohol and ether (especially methyl ether) content. Thus, late eluting fractions retain more of the characteristics of precursor material such as lignin and tannins suggesting that this material is newer/ less oxidized whereas late-eluting material represent the older/more oxidized material.
Publications and Collaborations
Brown, T.A.; Jackson, B.A.; Bythell, B.J.; Stenson*, A.C.; Benefits of multidimensional fractionation for the study and characterization of natural organic matter. Journal of Chromatography A (2016), 1470, 84-96. DOI: 10.1016/j.chroma.2016.10.005
Connell, M.; Stenson, A.C.; Weinrich, L.; LeChevallier, M.; Boyd, S.B.; Ghosal, R.R.; Dey, R.; Whelton*, A.J.; PEX and PP Water Pipes: Assimilable Carbon, Chemicals, and Odors. Journal - American Water Works Association (2016), 108, E192-E204. DOI: http://dx.doi.org/10.5942/jawwa.2016.108.0016.
Harris, B.D.; Brown, T.A.; McGehee, J.L.; Houserova, D.; Jackson, B.A.; Buchel, B.C.; Krajewski, L.C.; Whelton, A.J.; Stenson*, A.C.; Characterization of Disinfection Byproducts from Chromatographically Isolated NOM through High Resolution Mass Spectrometry. Environmental Science & Technology (2015), 49, 14239–14248. DOI: 10.1021/acs.est.5b03466.
Kelley, K.M.; Stenson, A.C.; Cooley, R.; Dey, R.; Whelton*, A.J.; The Cleaning Method Selected for New PEX Pipe Installation Can Affect Short-Term Drinking Water Quality. Journal of Water and Health (2015), 13, 960-969. DOI: 10.2166/wh.2015.243.
Stenson, A.C.; West, K.N.; Reichert, W.M.; Klomkaew,P,; Cassity, C.G.; Dobyns, B.M.; Siu,B.; Davis*, J.H., Jr.; Multi-cation ionic liquids and a direct, reproducible ‘non-mixing’ way to make them. Chemical Communications (2015), 51, 15914-15916. DOI: 10.1039/c5cc05843k.
*Novotny, N.R.; Capley, E.N.; Stenson*, A.C.; Fact or Artifact: The representativeness of ESI-MS for complex natural organic mixtures. Journal of Mass Spectrometry (2014), 49, 316-326.
*Stenson*, A.C.; Ruddy, B.M.; Bythell, B.J.; Ion Molecule Reaction H/D exchange as a Probe for Isomeric Fractionation in Chromatographically Separated Natural Organic Matter. International Journal of Mass Spectrometry (2014), 360, 45-53.
*Chen, L.; Mullen, G.E.; Le Roch, M.; Cassity, C.G.; Gouault, N.; Fadamiro, H.Y.; Barletta, R.E.; O'Brien, R.A.; Sykora, R.E.; Stenson, A.C.; West, K.N.; Horne, H.E.; Hendrich, J.M.; Xiang, K.R.; Davis*, J.H., Jr.; On the Formation of a Protic Ionic Liquid in Nature. Angewandte Chemie International Edition (2014), 53, 1-5.
Undergraduate Research Information
In this lab, we do analytical chemistry. Analytical chemists are essentially the detectives
of chemistry. We use clever techniques and instrumentation to discover what is in
a sample. The tools we use the most are HPLC (high pressure liquid chromatography)
to separate components of a sample from each other and MS (mass spectrometry) to identify
them. In addition, we use a host of tools and techniques ranging from state-of-the-art
to definitely very old-school (e.g., dialysis, extraction, metal-affinity chromatography,
hydrogen-deuterium exchange, even synthesis, when the situation calls for it). We
frequently have the most fun around here when we are a little bit out of our element
and have to discover how to work something new (or how to fix it).
The main analytical problem we tackle in this group is the structural characterization of aquatic humic substances (which are what organic matter such as trees and leaves decay to over time). This is a project as complex as the characterization of biomolecules was in its day, and arguably as important. For example, humic substances and humic-mimetics (synthetically made complex mixtures of compounds that we think resemble humic substances), have been shown to be virtual panaceas (i.e., medicine that can cure nearly anything; viral disease, bacterial disease, and cancer). Even more exciting, humics can do this without poisoning the host at the same time. They are so non-toxic, you could almost sprinkle them on your morning eggs (they even smell a little like herbal salt, though we don’t recommend you use them in that fashion). However, since humics and humic-mimetics are extremely diverse mixtures of compounds for which we do not know the structures, it is impossible to identify any particular active ingredients. Therefore, it is impossible to formulate any useful drugs until we know more, or at least identify some common structural features.
Besides working on humics and throwing any tool in the building at them (as well as
some you have to travel to Florida to use), we also work on collaborations with other
scientists. That is when we get to play with some pretty funky compounds. Some of
them come to us already charged; others balk at the valence rules we learned in freshmen
chemistry (e.g., Nitrogen with 4 bonds, Oxygen with 3). It can be a challenge to make
the instrument treat these molecules just right; not to break them up or fuse them
together. We also sometimes have to come up with ways to automate things or to trick
the instrument into more sensitivity. It’s these multifaceted applications and challenges
that keep analytical chemistry interesting and, at times, entertaining.