| Abstract
| - Brevetoxins, the toxic components of “red tide” algae, allshare one of two robust polycyclic ether backbone structures, but they are distinguished by differing side-chainsubstituents. Electrospray ionization mass spectrometryanalyses of brevetoxins have shown that the polyetherstructure invariably has a very high affinity for sodiumcations that results in the production of abundant (M +Na)+ ions even when sodium cations are only present asimpurities. Because the ionic charge tends to remainlocalized on the sodium atom and because at least twobonds must be broken in order to produce polycyclicbackbone fragmentation, it is extremely difficult to obtainabundant product ions (other than Na+) from (M + Na)+brevetoxin precursor ions in low-energy collision-induceddissociation (CID) MS/MS experiments. This report establishes that acid additives (oxalic acid, trifluoroaceticacid, and particularly hydrochloric acid) in aqueousmethanol solutions can promote high yields of protonatedbrevetoxin molecules (MH+ ions) for Btx-1, -2, and -9brevetoxins. Most importantly, unlike their (M + Na)+counterparts, MH+ precursor ions offer readily detectableproduct ions in CID MS/MS experiments, even under low-energy collisions. This direct structural characterizationapproach has provided decomposition information frombrevetoxins that was previously inaccessible, including theidentification of diagnostic product ions for “type A”brevetoxins (m/z 611) and “type B” brevetoxins (m/z779, 473, 179) and characteristic ions for Btx-1 (m/z221, 139), Btx-2 (m/z 153), and Btx-9 (m/z 157, 85).Precursor ion scans and constant neutral loss scans areproposed to enable screening of individual type A or typeB brevetoxins present in naturally occurring mixtures.
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