A simple, rapid liquid chromatography-tandem mass spectrometry method was developed to identify and quantitate in human urine the isoprostanes iPF 2a -III, 15-epiiPF 2a -III, iPF 2a -VI, and 8,12-iso-iPF 2a -VI along with the prostaglandin PGF 2a and 2,3-dinor-iPF 2a -III, a metabolite of iPF 2a -III. Assay specificity, linearity, precision, and accuracy met the required criteria for most analytes. The urine sample storage stability and standard solution stability were also tested.The methodology was applied to analyze 24 h urine samples collected from smokers and nonsmokers on controlled diets. The results for iPF 2a -III obtained by our method were significantly correlated with results by an ELISA, although an ?2-fold high bias was observed for the ELISA data. For iPF 2a -III and its metabolite 2,3-dinoriPF 2a -III, smokers had significantly higher concentrations than nonsmokers (513 6 275 vs. 294 6 104 pg/mg creatinine; 3,030 6 1,546 vs. 2,046 6 836 pg/mg creatinine, respectively). The concentration of iPF 2a -VI tended to be higher in smokers than in nonsmokers; however, the increase was not statistically significant in this sample set. Concentrations of the other three isoprostane isomers showed no trends toward differences between smokers and nonsmokers. Among smokers, the daily output of two type VI isoprostanes showed a weak correlation with the amount of tobacco smoke exposure, as determined by urinary excretion of total nicotine equivalents.-Yan, W., G. D. Byrd, and M. W. Ogden. Quantitation of isoprostane isomers in human urine from smokers and nonsmokers by LC-MS/MS.

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A pulsed laser has been used in conjunction with an ion cyclotron resonance spectrometer to generate and study the gas-phase ion-molecule reactions of Fe+ with simple carbonyl compounds and ethers. Oxidative addition reactions are observed, producing alkyl, acyl, and alkoxide intermediates which undergo intramolecular rearrangement by a 8-hydride shift mechanism. Decarbonylation reactions are observed with only a few small ketones. The main reaction channel is dehydrogenation for unbranched ketones and reductive elimination of methane for those branched at the (Y carbon. Reactions of Fe' with diisopropyl ketone, cyclohexanone, cyclopentanone, and tetrahydrofuran suggest the existence of intermediate and stable ?r-allyl complexes resulting from sequential @-hydride shifts.T o a solution chemist the direct cleavage of carbon-carbon bonds by transition metals is not as common a process as carbon-carbon bond formation. T o the gas-phase ion-molecule chemist, however, carbon+arbon bond cleavage by atomic metal ions and metal-ion complexes may be a more common occurrence.

Poison frogs sequester chemical defenses from arthropod prey, although the details of how arthropod diversity contributes to variation in poison frog toxins remains unclear. We characterized skin alkaloid profiles in the Little Devil poison frog, Oophaga sylvatica (Dendrobatidae), across three populations in northwestern Ecuador. Using gas chromatography/mass spectrometry, we identified histrionicotoxins, 3,5- and 5,8-disubstituted indolizidines, decahydroquinolines, and lehmizidines as the primary alkaloid toxins in these O. sylvatica populations. Frog skin alkaloid composition varied along a geographical gradient following population distribution in a principal component analysis. We also characterized diversity in arthropods isolated from frog stomach contents and confirmed that O. sylvatica specialize on ants and mites. To test the hypothesis that poison frog toxin variability reflects species and chemical diversity in arthropod prey, we (1) used sequencing of cytochrome oxidase 1 to identify individual prey specimens, and (2) used liquid chromatography/mass spectrometry to chemically profile consumed ants and mites. We identified 45 ants and 9 mites in frog stomachs, including several undescribed species. We also showed that chemical profiles of consumed ants and mites cluster by frog population, suggesting different frog populations have access to chemically distinct prey. Finally, by comparing chemical profiles of frog skin and isolated prey items, we traced the arthropod source of four poison frog alkaloids, including 3,5- and 5,8-disubstituted indolizidines and a lehmizidine alkaloid. Together, the data show that toxin variability in O. sylvatica reflects chemical diversity in arthropod prey.