Practice and Principles of Isotopic Measurements in Organic Geochemistry

These notes have been compiled from teaching materials developed by John Hayes between 1980 and 1995. Since their goals are to introduce basic concepts and practices, they are not grossly outdated in spite of their antiquity. Where necessary or desirable, minimal revisions indicate more recent data and practices. The sections include: Practice and Principles of Isotopic Measurements in Organic Geochemistry. This review originally appeared as pp. 5-1 to 5-31 in W. G. Meinschein (ed.) Organic Geochemistry of Contemporaneous and Ancient Sediments, a volume published in 1983 by the Great Lakes Section of the Society of Economic Pale-ontologists and Mineralogists. That book was intended to provide the notes for a short course offered in connection with the 1983 National Meeting of the Geological Society of America, but the short course drew inadequate enrollment and was cancelled. The original document included the introduction and sections 1 and 2 reprinted here, as well as an earlier version of section 3. Primary Standards of Stable Isotopic Abundances. Presented here as section 3, this material was revised and expanded frequently in the years after 1983, notably for use in a short course sponsored by Finnigan MAT in Beijing in 1986 and for frequent use in subsequent classes at Indiana University. Limits on the Precision of Mass Spectrometric Measurements of Isotope Ratios. Originally prepared for class use some time in the 1980s, this text (Section 4) explains how shot noise, or " ion-beam noise, " or " ion statistics " fundamentally limit the precision that can be attained in any measurement based on integration of an electrical current. Uncertainties in Blank-Corrected Isotopic Analyses. These notes (Section 5) were prepared for use by workers in the Biogeochemical Laboratories at Indiana University during the 1980's (accordingly, their presentation is far from " publishable "). They deal with the common problem in which an analytical result reflects the composition of a sample and, in addition, the magnitude and isotopic composition of an analytical blank. Further Notes, July 2002. Section 6 elaborates on notes inserted in earlier sections.