@article {587,
	title = {Calculation of hydrogen isotopic fractionations in biogeochemical systems},
	journal = {Geochimica Et Cosmochimica Acta},
	volume = {69},
	year = {2005},
	note = {892wiTimes Cited:55Cited References Count:21},
	month = {Feb 1},
	pages = {593-597},
	abstract = {Hydrogen-isotopic data are often interpreted using mathematical approximations originally intended for other isotopes. One of the most common. apparent in literature over the last several decade{\textquoteright}s. assumes that delta values of reactants and products are separated by a constant fractionation factor delta(p) = delta(r) + epsilon(p/r). Because of the large fractionations that affect hydrogen isotopes, such approximations can lead to substantial errors. Here we review and develop general equations for isotopic mass balances that include the differential fractionation of each component in a mixture and discuss their use in three geochemical applications. For the fractionation of a single component. the reactant and product are related by delta(p) = a(p/r)delta(r) + epsilon(p/r), where alpha and epsilon refer to the same fractionation. Regression of delta(p) on delta(r) should give equivalent fractionations based on the intercept and slope, but this has not generally been recognized in studies of D/H fractionation. In a mixture of two components, each of which is fractionated during mixing, there is no unique solution for the three unknown variables (two fractionation factors and the elemental mixing ratio of the two hydrogen sources). The flow of H from CH4 and H2O to bacterial lipids in the metabolism of Methylococcus capsulatus provides an example of such a case. Data and conclusions from an earlier study of that system (Sessions et al., 2002) are reexamined here. Several constraints on the variables are available based on plausible ranges for fractionation factors. A possible refinement to current experimental procedures is the measurement of three different isotopes, which would allow unique determination of all variables. Copyright (C) 2005 Elsevier Ltd.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2004.08.005},
	author = {Sessions, A. L. and Hayes, J. M.}
}
@article {640,
	title = {Moving-wire device for carbon isotopic analyses of nanogram quantities of nonvolatile organic carbon},
	journal = {Anal Chem},
	volume = {77},
	year = {2005},
	note = {Sessions, Alex LSylva, Sean PHayes, John MengResearch Support, U.S. Gov{\textquoteright}t, Non-P.H.S.2005/10/15 09:00Anal Chem. 2005 Oct 15;77(20):6519-27.},
	month = {Oct 15},
	pages = {6519-27},
	abstract = {We describe a moving-wire analyzer for measuring 13C in dissolved, involatile organic materials. Liquid samples are first deposited and dried on a continuously spooling nickel wire. The residual sample is then combusted as the wire moves through a furnace, and the evolved CO2 is analyzed by continuous-flow isotope ratio mass spectrometry. A typical analysis requires 1 microL of sample solution and produces a CO2 peak approximately 5 s wide. The system can measure "bulk" delta13C values of approximately 10 nmol of organic carbon with precision better than 0.2 per thousand. For samples containing approximately 1 nmol of C, precision is approximately 1 per thousand. Precision and sensitivity are limited mainly by background noise derived from carbon within the wire. Instrument conditions minimizing that background are discussed in detail. Accuracy is better than 0.5 per thousand for nearly all dissolved analytes tested, including lipids, proteins, nucleic acids, sugars, halocarbons, and hydrocarbons. The sensitivity demonstrated here for 13C measurements represents a approximately 1000-fold improvement relative to existing elemental analyzers and should allow the use of many new preparative techniques for collecting and purifying nonvolatile biochemicals for isotopic analysis.},
	issn = {0003-2700 (Linking)},
	doi = {10.1021/ac051251z},
	author = {Sessions, A. L. and Sylva, S. P. and Hayes, J. M.}
}
@article {464,
	title = {A gas ion source for continuous-flow AMS},
	journal = {Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry},
	volume = {223-224},
	year = {2004},
	note = {id: 2104},
	pages = {149-154},
	abstract = {The first gas-fed ion source for radiocarbon AMS applications (without sputtering) has been operated at the Woods Hole NOSAMS Facility. A three-year, off-line test program resulted in positive carbon ion currents up to 1 mA and negative ion currents up to 80 μA. Recently, the compact, permanent-magnet microwave plasma ion source and magnesium vapor charge-exchange canal were coupled to the recombinator injector of the 2.5 MV Tandetron. When the ion source was operated on CO2 at a flow rate of about 200 μl per minute, negative carbon ion beams up to 20 μA were obtained, at an energy of 35 keV. Radiocarbon measurements were performed on standard reference gases and the dynamic response to square-wave pulses of gas was determined. Time constants in the ion source are less than 1 s, which should allow analysis of chromatographic peaks of CO2 with very little broadening. A combustion device has been constructed to generate CO2 for direct injection into the source. Argon carrier gas is used to buffer the pressure at one atmosphere in the sample gas injector. A dedicated ion-beam injector, with higher angular acceptance and higher transmitted currents, is being constructed for the AMS system.},
	issn = {0168-583X},
	doi = {10.1016/j.nimb.2004.04.031},
	author = {Schneider, R. J. and Kim, S. W. and von Reden, K. F. and Hayes, J. M. and Wills, J. S. C. and Griffin, V. S. and Sessions, A. L. and Sylva, S.}
}
@article {830,
	title = {Compound-specific D/H ratios of lipid biomarkers from sediments as a proxy for environmental and climatic conditions},
	journal = {Geochimica Et Cosmochimica Acta},
	volume = {65},
	year = {2001},
	note = {395npTimes Cited:209Cited References Count:64},
	month = {Jan},
	pages = {213-222},
	abstract = {Hydrogen isotope ratios (D/H) of lipid biomarkers extracted from aquatic sediments were measured to determine whether they can be used as a proxy for D/H of environmental water. Values of deltaD were determined by using a recently developed isotope-ratio-monitoring gas chromatograph-mass spectrometer system (irmGCMS) and were confirmed by conventional hydrogen isotopic measurements (i.e., combustion followed by reduction) on individual compounds isolated by preparative capillary gas chromatography. Diverse lipids (alkanes, n-alkanols, sterols, and pentacyclic triterpenols) were analyzed to examine hydrogen-isotopic controls on lipids of varying origin and biosynthetic pathway. For algal sterols (24-methylcholest-3 beta -ol, 24-ethylcholest-5,22-dien-3 beta -ol, and 4,23,24-trimethylcholesterol, or dinosterol), the fractionation between sedimentary lipids and environmental water was -201 +/- 10 parts per thousand and was similar in both marine and freshwater sites. In a sediment from a small lake in a forested catchment, triterpenols from terrestrial sources were enriched in D by 30 parts per thousand relative to algal sterols. Apparent fractionation factors for n-alkyl lipids were smaller than those of triterpenols and were more variable, probably reflecting multiple sources for these compounds. We conclude that hydrogen-isotopic analyses of algal sterols provide a viable means of reconstructing D/H of environmental waters. Results are less ambiguous than reconstructions based on analyses of kerogen or other operationally defined organic matter fractions. Copyright (C) 2001 Elsevier Science Ltd.},
	issn = {0016-7037},
	doi = {10.1016/S0016-7037(00)00520-2},
	author = {Sauer, P. E. and Eglinton, T. I. and Hayes, J. M. and Schimmelmann, A. and Sessions, A. L.}
}
@article {2129,
	title = {Correction of H3+ contributions in hydrogen isotope ratio monitoring mass spectrometry},
	journal = {Anal Chem},
	volume = {73},
	year = {2001},
	note = {Sessions, A LBurgoyne, T W
Hayes, J M
eng
2001/02/24 12:00
Anal Chem. 2001 Jan 15;73(2):192-9.
},
	month = {Jan 15},
	pages = {192-9},
	abstract = {Two fundamentally different approaches, termed "pointwise" and "peakwise," are currently used to correct hydrogen isotope ratio monitoring data for the presence of H3+ ion contributions. Consideration of the underlying assumptions shows that the peakwise approach is valid only for peaks with the same functional shape and only when background signals do not vary. The pointwise correction is much more versatile and can be used even when peak shapes and sizes, as well as background signals, vary significantly. It is not exact and is limited in accuracy by (1) the signal-broadening effects of electronic time constants, (2) the analog-to-digital conversion frequency, and (3) the highest frequency of the sample signal. To minimize errors for typical gas chromatographic signals, time constants of <500 ms and analog-to-digital sampling intervals of < or =250 ms are needed. Errors are further minimized by matching sample and standard peaks in both amplitude and D/H ratio. Using the pointwise algorithm, we demonstrate that a series of 14 homologous n-alkanes varying in concentration over a 5-fold range can be analyzed with a mean precision of 2.3 per thousand and no systematic errors.},
	isbn = {0003-2700 (Print)0003-2700 (Linking)},
	doi = {10.1021/ac000489e},
	url = {https://www.ncbi.nlm.nih.gov/pubmed/11199965},
	author = {Sessions, A. L. and Burgoyne, T. W. and Hayes, J. M.}
}
@article {2128,
	title = {Determination of the the H3 factor in hydrogen isotope ratio monitoring mass spectrometry},
	journal = {Anal Chem},
	volume = {73},
	year = {2001},
	note = {Sessions, A LBurgoyne, T W
Hayes, J M
eng
2001/02/24 12:00
Anal Chem. 2001 Jan 15;73(2):200-7.
},
	month = {Jan 15},
	pages = {200-7},
	abstract = {The H3 factor, K, is a parameter required in high-precision, mass spectrometric analyses of hydrogen isotopic abundances. When H2 is used as the sample gas, R* = R - Ki2, where R* is the true HD/H2 ratio, R is the observed (mass 3)/(mass 2) ion-current ratio, and i2 is the ion current at mass 2. Four different methods for the determination of K were defined and tested under conditions characteristic of isotope ratio monitoring systems. Three of these were peak-based. The fourth employed steady flows of H2 from a conventional inlet system. Results obtained using the latter method were more precise (standard deviation of K = 0.1 versus approximately 0.6 ppm mV(-1) for the peak-based methods). However, use of the resulting values of K for correction of isotope ratio monitoring GC/MS results led to systematic errors as large as 9 per thousand, whereas use of the peak-based values led to no systematic errors. Values of K were only weakly dependent on the pressure of He, declining approximately 5\% for each 10-fold increase in P(He). Small variations in partial pressures of H2O and CH4, potential contaminants under isotope ratio monitoring conditions, had no significant effect on values of K.},
	isbn = {0003-2700 (Print)0003-2700 (Linking)},
	doi = {10.1021/ac000488m},
	url = {https://www.ncbi.nlm.nih.gov/pubmed/11199966},
	author = {Sessions, A. L. and Burgoyne, T. W. and Hayes, J. M.}
}
@article {811,
	title = {Fractionation of hydrogen isotopes in lipid biosynthesis},
	journal = {Organic Geochemistry},
	volume = {30},
	year = {1999},
	note = {254efTimes Cited:281Cited References Count:26},
	pages = {1193-1200},
	abstract = {Isotopic compositions of carbon-bound hydrogen in individual compounds from eight different organisms were measured using isotope-ratio-monitoring gas chromatography-mass spectrometry. This technique is capable of measuring D/H ratios at natural abundance in individual lipids yielding as little as 20 nmol of H-2, and is applicable to a wide range of compounds including hydrocarbons, sterols, and fatty acids. The hydrogen isotopic compositions of lipids are controlled by three factors: isotopic compositions of biosynthetic precursors, fractionation and exchange accompanying biosynthesis, and hydrogenation during biosynthesis. delta D values of lipids from the eight organisms examined here suggest that all three processes are important for controlling natural variations in isotopic abundance. n-Alkyl lipids are depleted in D relative to growth water by 113-262 parts per thousand, while polyisoprenoid lipids are depleted in D relative to growth water by 142-376 parts per thousand. Isotopic variations within compound classes (e.g., n-alkanes) are usually less than similar to 50 parts per thousand, but variations as large as 150 parts per thousand are observed among isoprenoid lipids from a single organism. Phytol is consistently depleted in D by up to 50 parts per thousand relative to other isoprenoid lipids. Inferred isotopic fractionations between cellular water and lipids are greater than those indicated by previous studies. (C) 1999 Elsevier Science Ltd. All rights reserved.},
	issn = {0146-6380},
	doi = {10.1016/S0146-6380(99)00094-7},
	author = {Sessions, A. L. and Burgoyne, T. W. and Schimmelmann, A. and Hayes, J. M.}
}
