Isotope ratio measurements: new developments and applications

Abstract

After 2004 and 2008 (Vols. 378/2 and 390/2) this is the third issue of Analytical and Bioanalytical Chemistry to contain papers on new developments and applications in isotope ratio measurements. Whereas Klaus Heumann was guest editor for the two previous special issues, in this issue Torsten Schmidt joins him as guest editor for the first time. His involvement with this collection of papers strongly reflects the increasing importance of compound-specific stable isotope analysis, one of his core research areas, on which, with Maik Jochmann, he has recently published a monograph “Compound-specific Stable Isotope Analysis” (see corresponding book review in this issue). A total of 24 manuscripts describing new instrumentation, methodological questions, for example normalization and the use of certified isotope reference materials, isotope-labeling experiments, determination of natural isotope signatures, applications in archeology and in clinical and nuclear chemistry, and isotope dilution analysis demonstrate the broad range of modern precise and accurate isotope ratio measurements. This great variety of applications also clearly shows that increasing attention is being focused on isotope ratio determinations in modern analytical chemistry. A recently published textbook “Isotopic Analysis” by Frank Vanhaecke and Patrick Degryse, which is also reviewed in this issue, confirms this trend. Another interesting trend compared with the earlier collections of papers on this topic is that thermal ionization mass spectrometry (TIMS) is no longer predominant in current applications. Although TIMS still has some important niches of application in nuclear and geochemistry, it has frequently been substituted by ICP–MS, because of its advantages of simpler sample preparation and multi-element capability and also because some elements, for example refractory and precious metals, are not easily accessible to TIMS. On the other hand, gas chromatography coupled with an isotope ratio mass spectrometer (GC–IRMS) and a combustion interface for converting organic molecules into CO2 and N2 for C/C and N/N ratio measurements, respectively, by electron impact ionization is increasingly used for new applications in compound-specific isotope analysis. Furthermore, the more recently introduced hyphenation with liquid chromatography for carbon-isotope analysis of compounds not or hardly amenable to GC separation has been demonstrated. One “Technical Note” reports the first isotope ratio measurements with a commercially available Mattauch– Herzog ICP–MS, which was constructed for simultaneous mass detection. However, future improvements of this instrument will show whether this type of mass spectrometer can become an alternative to high-resolution multi-collector systems for precise isotope ratio determinations. A Feature Article by Willi Brand on “Atomic weights: not so constant after all” may be of general interest to all natural scientists. This article explains why IUPAC’s Commission on Isotopic Abundances and Atomic Weights recently decided to substitute fixed atomic weights for ten elements by atomic weight intervals. More precise isotope ratio measurements of the isotope variation of the corresponding natural and commercial substances during the last two decades led to this decision. Whereas for the light elements, for example hydrogen, carbon, and oxygen, isotope variations have been known for a long time, those for heavy metals, for example thallium, which is one of the ten elements for which the change has been made, were discovered by highly precise isotope ratio measurements especially by use of multi-collector (MC)-ICP–MS systems. This substantial improvement in isotope ratio determinations is Published in the topical collection Isotope Ratio Measurements: New Developments and Applications with guest editors Klaus G. Heumann and Torsten C. Schmidt.