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Hydrogen Isotope Ratios of Individual Organic Compounds

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Hydrogen Isotope Ratios of Individual Organic Compounds HYDROGEN ISOTOPE RATIOS OF INDIVIDUAL ORGANIC COMPOUNDS Alex L. Sessions Submitted to the faculty of the University Graduate School in partial fulfillment of the requirements for the degree Doctor of Philosophy in the Department of Geological Sciences Indiana University August, 2001 i Acknowledgements The completion of this thesis is due to the patient advice and kind help of many, many people. Foremost among them is Dr. John Hayes, who has worked tirelessly to teach me not only the fundamentals, but the art of conducting scientific research. The depth and breadth of my education under him has been remarkable, and I am deeply grateful. I can think of no better compliment than the fact that I am eagerly staying on as a post-doc under his direction. My advising committee, Drs. Simon Brassell, Tim Eglinton, Gary Hieftje, and Arndt Schimmelmann, also deserve a hearty thank-you. They have been encouraging and supportive as I progressed through the Ph.D. program, and each one has answered more than his share of ridicu- lous questions (Why does D2O kill bugs?) My parents – who also deserve a great deal of credit for encouraging an inquistive mind and love of science – sympathize with you all. Two people in particular are responsible for teaching me the nuts and bolts of isotope geochemistry. Dr. Tom Burgoyne, a post-doc at Bloomington, coached me in the fine points of using, fixing, and understanding mass spectrometers. Dr. Chris Reddy, a post-doc and later assistant scientist at WHOI, showed me how to work in an organic geochemistry laboratory. It is a rare day that I do not use some technique, trick, or rule of thumb that they taught me. Many other folks have helped me with this thesis in countless ways. Arndt Schimmelmann performed offline δD measurements of all our organic standards, and of the culture media and gases used in Chapter 5. Peter Sauer helped collect specimens for our first D/H analyses (Chapter 1), and Great Pond sediment for exchange experiments. Sean Sylva helped prepare, extract, and analyze the hydrogen exchange experiments (Chapter 4). Linda Jahnke grew Methylococcus capsulatus, and Kathleen Londry grew sulfate-reducing bacteria, which together comprise Chapter 5. Roger Summons provided numerous consultations over mass spectra. Other helpful folks include: Steve Studley, Julie Primack, Kristen Leckrone, Lisa Pratt, Jennifer Villinski, and Jon Fong at Indiana University; Daniel Montlucon, Jeff Seewald, Kai-Uwe Hinrichs, Paul Fucile, Carl Johnson, Leah Houghton, and the entire staff of NOSAMS at WHOI. Financial support during the past five years has been provided by a fellowship from the University Graduate School at Indiana University; by grants to John Hayes from NASA and the National Science Foundation; through John Hayes’ WHOI research funds; and by a generous grant from Royal Dutch Shell, arranged by Dr. Olaf Podlaha. Last and most importantly, I would not have made it this far without my wife, Karen. She has supported and encouraged me in every way possible. Many thanks to all of you. ii Preface When I first met John Hayes in February, 1996, he suggested that the development of continuous-flow hydrogen-isotopic analyses might be a good thesis project. While I scarcely understood what ‘continuous-flow’ meant at the time, the project sounded exciting and I ac- cepted. Thus began a five-year project involving myself, John Hayes, Tom Burgoyne, and Arndt Schimmelmann. By the spring of 1997 work was underway. Tom quickly developed high-tem- perature pyrolysis as an efficient means for converting organic hydrogen to H2, work that was later published in Analytical Chemistry (1998, 70:5136-5141). Meanwhile, Arndt and I struggled to perfect a Pd filter for separating H2 from He. That approach quickly fizzled, and I began to systematically study the problem of H3 correction in continuous flow hydrogen analyses. In preparation for improvements to come, I began to develop the Excel macros that Tom would eventually dub ‘AlexDAT’ after the Finnigan software of a similar name. By the spring of 1998, we were testing our second prototype of the ‘ED,’ an energy-dis- criminating lens that Tom designed and built to suppress low-energy He+. In June, I moved my family and the partially-developed hydrogen system to Woods Hole to continue work in John’s new labs. A discouraging summer of testing and rebuilding the ED followed, but by the fall the ED had evolved enough to allow us to make our first crude D/H measurements of real samples. We quickly discovered that many, if not all, organic geochemical laboratories are rife with the perdeuterated compounds used as internal standards for GC. To facilitate more rapid progress, John and I scoured the WHOI biology department in search of suitable phytoplankton cultures, and in February, 1999, Peter Sauer and I collected the plants from Woods Hole Harbor that eventually formed the basis for our 1999 Organic Geochemistry paper (Chapter 1). With an initial publication under our belt, in the summer of 1999 we turned back to refining analytical tech- niques, working both on perfecting H3 corrections and on eliminating the GC peak-tailing that had plagued us from the earliest days. Work on H3 corrections eventually culminated in the publication of back-to-back papers in Analytical Chemistry in December, 2000 (Chapters 2 and 3). But despite the helpful suggestions from many gurus of gas chromatography, we never solved the peak-tailing problems, though (much to our chagrin) Andreas Hilkert in Bremen did. By the fall of 1999 Tom had moved to Oklahoma State, the hydrogen system was largely functional, and our research interests diverged. I began dabbling with hydrogen exchange experiments, and travelled to Moffett Field to learn how to grow Methylococcus capsulatus from the master, Linda Jahnke. The period from fall, 1999, to spring, 2001 was spent producing the data that appears in Chapters 4 and 5. The purposes of this rambling preface are twofold. The first is to provide a historical perspective for the D/H project. This thesis chronicles only the parts of the project for which I was primarily responsible. The chapters of the thesis are presented as they were written, in chronological order, rather than in some logical progression of topics. Chapters 1–3 have been reproduced in the form they appeared in publication, complete with abstract and references. For consistency, chapters 4 and 5 follow this format, though they have not yet been submitted for publication. The second purpose of this preface is to emphasize that this project has been a team effort in every sense, and while each of us was responsible for different aspects of it, none of the work reported here (or elsewhere) would have been possible without the individual contributions of all four scientists. iii Table of Contents Acknowledgements ........................................................................................................... ii Preface ............................................................................................................................... iii Chapter 1 — Fractionation of hydrogen isotopes in lipid biosynthesis ....................... 1 Abstract ..................................................................................................................................... 1 Introduction ............................................................................................................................... 2 Experimental ............................................................................................................................. 3 Isotopic Measurements ....................................................................................................... 3 Sample Collection and Preparation .................................................................................... 5 Results and Discussion ............................................................................................................. 5 Variations of δD Within Organisms ................................................................................... 8 Isotopic Fractionation ....................................................................................................... 10 Variations of δD Between Organisms .............................................................................. 11 Conclusions ............................................................................................................................. 12 References ............................................................................................................................... 13 + Chapter 2 — Correction of H3 contributions in hydrogen isotope-ratio-monitoring mass spectrometry .................................................................................................... 15 Abstract ................................................................................................................................... 15 Introduction ............................................................................................................................. 16 Theory ..................................................................................................................................... 16 + H3 Correction Algorithms ................................................................................................ 18 Peakwise Corrections ....................................................................................................... 19 Pointwise Corrections .....................................................................................................
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