Isotope Ratio Mass Spectrometry

Tracing patterns of erosion and drainage in the Paleogene Himalaya through ion probe Pb isotope analysis of detrital K-feldspars in the Indus Molasse, India

by Peter Clift

Oceanic molybdenum isotope fractionation: Diagenesis and hydrothermal ridge-flank alteration

by Chris Siebert

Molybdenum isotope signatures in continental margin marine sediments

by Chris Siebert

PGE, Re-Os and Molybdenum isotope systematicsin Archean and early Proterozoic sedimentary systems as proxies for redox conditions of the early Earth

by Chris Siebert

Molybdenum isotope records as a potential new proxy for paleoceanography

by Chris Siebert

Determination of Molybdenum Isotope Fractionation by Double Spike MC-ICP-MS

by Chris Siebert

Proteome turnover in the green alga Ostreococcus tauri by time course 15N metabolic labeling mass spectrometry

by Sarah Martin

Journal of Proteome Research
Martin SF, Munagapati VS, Salvo-Chirnside E, Kerr L, Le Bihan, T

Protein synthesis and degradation determine the cellular levels of proteins, and their control hence enables organisms... more Protein synthesis and degradation determine the cellular levels of proteins, and their control hence enables organisms to respond to environmental change. Experimentally, these are little known proteome parameters, however recently, SILAC-based mass spectrometry studies have begun to quantify turnover in the proteomes of cell lines, yeast and animals. Here, we present a proteome-scale method to quantify turnover and calculate synthesis and degradation rate constants of individual proteins in autotrophic organisms such as algae and plants. The workflow is based on the automated analysis of partial stable isotope incorporation with ¹⁵N. We applied it in a study of the unicellular pico-alga <i>Ostreococcus tauri</i> and observed high relative turnover in chloroplast-encoded ATPases (0.42%-0.58% h^-1), core photosystem II proteins (0.34%-0.51% h^-1) and RbcL (0.47% h^-1), while nuclear-encoded RbcS2 is more stable (0.23% h^-1). Mitochondrial targeted ATPases (0.14%-0.16% h^-1), photosystem antennae (0.09%-0.14% h^-1) and histones (0.07%-0.1% h^-1) were comparatively stable. The calculation of degradation and synthesis rate constants k_deg and k_syn confirms RbcL as the bulk contributor to overall protein turnover. This study performed over 144h of incorporation reveals dynamics of protein complex subunits as well as isoforms targeted to different organelles.

Liquid chromatography/isotope ratio mass spectrometry measurement of δ13C of amino acids in plant proteins

by Tony Lynch

Rapid Communications in Mass Spectrometry, 2011, 25(20), 2981-2988

In archaeological studies, the isotopic enrichment values of carbon and nitrogen in bone collagen give a degree of... more In archaeological studies, the isotopic enrichment values of carbon and nitrogen in bone collagen give a degree of information on dietary composition. The isotopic enrichments of individual amino acids from bone collagen and dietary protein have the potential to provide more precise information about the components of diet. A limited amount of work has been done on this, although the reliability of these studies is potentially limited by fractionation arising through hydrolysis of whole plant tissue (where reaction between amino acids and carbohydrates may occur) and, for certain amino acids, the use of derivatives (particularly trifluoroacetyl derivatives) for gas chromatography/isotope ratio mass spectrometry (GC/IRMS) analysis. The present study takes the approach of extracting the protein components of plant tissues before hydrolysis and using liquid chromatography/isotope ratio mass spectrometry (LC/IRMS), which does not require derivatisation, for measurement of the isotopic enrichment of the amino acids. The protocol developed offers a methodology for consistent measurement of the δ13C values of amino acids, allowing isotopic differences between the individual amino acids from different plant tissues to be identified. In particular, there are highly significant differences between leaf and seed protein amino acids (leaf minus grain) in the cases of threonine (-4.1%), aspartic acid (+3.5%) and serine (-3.2%). In addition to its intended application in archaeology, the technique will be of value in the fields of plant sciences, nutrition and environmental food-web studies. © 2011 John Wiley & Sons, Ltd.

Fingerprints for Main Varieties of Argentinean Wines: Terroir Differentiation by Inorganic, Organic, and Stable Isotopic Analyses Coupled to Chemometrics

by Ernesto Gallegos

Our main goal was to investigate if robust chemical fingerprints could be developed for three Argentinean red winesmore Our main goal was to investigate if robust chemical fingerprints could be developed for three Argentinean red wines
based on organic, inorganic, and isotopic patterns, in relation to the regional soil composition. Soils and wines from three regions
(Mendoza, San Juan, and C
ordoba) and three varieties (Cabernet Sauvignon, Malbec, and Syrah) were collected. The phenolic
profile was determined by HPLC-MS/MS and multielemental composition by ICP-MS; 87Sr/86Sr and δ13C were determined by
TIMS and IRMS, respectively. Chemometrics allowed robust differentiation between regions, wine varieties, and the same variety
from different regions. Among phenolic compounds, resveratrol concentration was the most useful marker for wine differentiation,
whereas Mg, K/Rb, Ca/Sr, and 87Sr/86Sr were the main inorganic and isotopic parameters selected. Generalized Procrustes analysis
(GPA) using two studied matrices (wine and soil) shows consensus between them and clear differences between studied areas.
Finally, we applied a canonical correlation analysis, demonstrating significant correlation (r = 0.99; p < 0.001) between soil and wine
composition. To our knowledge this is the first report combining independent variables, constructing a fingerprint including
elemental composition, isotopic, and polyphenol patterns to differentiate wines, matching part of this fingerprint with the soil
provenance.

A counter-intuitive approach to calculating non-exchangeable 2H isotopic composition of hair: treating the molar exchange fraction fE as a process-related rather than compound-specific variable

by Wolfram Meier-Augenstein

The results reported in this paper clearly demonstrate the matter of exchangeable H in organic compounds such as keratin is not a trivial one and must be properly addressed for 2H isotope abundance data to form a solid foundation to base on any scientific or forensic conclusions.

Hair is a keratinous tissue that incorporates hydrogen from material that an animal consumes but it is metabolically... more Hair is a keratinous tissue that incorporates hydrogen from material that an animal consumes but it is metabolically inert following synthesis. The stable hydrogen isotope composition of hair has been used in ecological studies to track migrations of mammals as well as for forensic and archaeological purposes to determine the provenance of human remains or the recent geographic life trajectory of living people. Measurement of the total hydrogen isotopic composition of a hair sample yields a composite value comprised of both metabolically informative, nonexchangeable hydrogen and exchangeable hydrogen, with the latter reflecting ambient or sample preparation conditions. Neither of these attributes is directly measurable, and the non-exchangeable hydrogen composition is obtained by estimation using a commonly applied mathematical expression incorporating sample measurements obtained from two distinct equilibration procedures. This commonly used approach treats the fraction of exchangeable hydrogen as a mixing ratio, with a minimal procedural fractionation factor assumed to be close or equal to 1.
Instead, we propose to use full molar ratios to derive an expression for the non-exchangeable hydrogen composition explicitly as a function of both the procedural fractionation factor a and the molar hydrogen exchange fraction fE. We apply these derivations in a longitudinal study of a hair sample and demonstrate that the molar hydrogen exchange fraction fE should, like the procedural fractionation factor a, be treated as a process-dependent parameter, i.e. a reaction-specific constant. This is a counter-intuitive notion given that maximum theoretical values for the molar hydrogen exchange fraction fE can be calculated that are arguably protein-type specific and, as such, fE could be regarded as a compound-specific constant. We also make some additional suggestions for future approaches to determine the non-exchangeable hydrogen composition of hair and the use of standards.

Evidence for bias in C/N, δ13C and δ15N values of bulk organic matter, and on environmental interpretation, from a lake sedimentary sequence by pre-analysis acid treatment methods.

by Chris Brodie

In Press - Quaternary Science Reviews

Lead Author: Dr. Chris Brodie (Hong Kong University, Hong Kong)

Co-Authors: Dr. James Casford (Durham University); Dr. Jeremy Lloyd (Durham University, UK); Prof. Melanie Leng (NIGL, UK); Dr. Timothy Heaton (NIGL, UK); Christopher Kendrick (NIGL, UK); Dr. Zong Yongqiang (Hong Kong University, Hong Kong).

ABSTRACT:
There is a known bias in C/N, d13C and d15N values of organic matter (OM) due to pre-analysis acid... more ABSTRACT:
There is a known bias in C/N, d13C and d15N values of organic matter (OM) due to pre-analysis acid treatment methods. We report here, for the first time, the results of a pre-analysis acid treatment method comparison of measured C/N, d13C and d15N values in bulk OM from a sedimentary sequence of samples to illustrate this bias. Here we show that acid treatment significantly reduces the accuracy (between method biases) and precision (within method bias) of C/N, d13C and d15N values of OM, suggesting a differential response of sample OM between methods and sample horizons, and in some cases inefficient removal of inorganic carbon. We show that different methods can significantly influence environmental interpretation in some of our sample horizons (i.e. interpretation of aquatic vs. terrestrial OM source; C3 vs. C4 vegetation). Specifically, there are unpredictable and non-linear differences between methods for C/N values in the range of ~ 1 – 100; d13C values in the range of 0.2 – 6.8 ‰ and; d15Nvalues in the range of 0.3 – 0.7 ‰. Importantly, these ranges are mostly much greater than the instrument precision (defined as the standard deviation of replicate analysis of standard reference materials; for this study, ± 0.5 for C/N values, ± 0.1 ‰ for d13C values and; ± 0.1 ‰ for d15N). The accuracy and precision of measured C/N, d13C and d15N values of bulk OM is not just dependent upon environmental variability, but on acid pre-treatment, residual inorganic carbon and organic matter state and composition. Collectively, this makes the correlation between samples prepared in different ways, including those from down core reconstructions, highly questionable.

Keywords: C/N ratios, δ13C, δ15N, organic matter; pre-analysis acid treatment methods, environmental interpretation, palaeoclimate.

Variability in oxidative degradation of charcoal: influence of production variables and environmental exposure

by Philippa Ascough

Published in Geochimica et Cosmochimica Acta Vol.75, p2361-2378 (doi:10.1016/j.gca.2011.02.002)

Charcoal is a key component of the Black Carbon (BC) continuum, where BC is characterized as a recalcitrant,... more Charcoal is a key component of the Black Carbon (BC) continuum, where BC is characterized as a recalcitrant, fire-derived, polyaromatic material. Charcoal is an important source of palaeoenvironmental data, and of great interest as a potential carbon sink, due to its high apparent environmental stability. However, at least some forms of charcoal are clearly susceptible to environmental alteration and degradation over relatively short timescales. Although these processes have importance for the role of charcoal in global biogeochemistry, they remain poorly understood.
Here we present results of an investigation into the susceptibility of a range of charcoal samples to oxidative degradation in acidified potassium dichromate. The study examines both freshly produced charcoal, and charcoal exposed to environmental conditions for up to 50,000 years. We compare the proportion of carbon present in different forms between the samples, specifically with respect to the relative chemical resistance of these forms. This was undertaken in order to improve understanding of the post-depositional diagenetic changes affecting charcoal within environmental deposits.
A wide range in chemical compositions are apparent both within and between the sample groups. In freshly produced charcoal, material produced at 300°C contains carbon with more labile forms than charcoal produced at ≥400°C, signifying a key chemical change over the 300-400°C temperature range. Charcoal exposed to environmental depositional conditions is frequently composed of a highly carboxylated aromatic structure and contains a range of carbon fractions of varying oxidative resistance. These findings suggest that a significant number of the environmental charcoals have undergone post-depositional diagenetic alteration. Further, the data highlight the potential for the use of controlled progressive oxidative degradation as a method to characterize chemical differences between individual charcoal samples.

Keywords
Charcoal, Oxidative degradation, Black carbon, Biochar

Evidence for bias in measured δ15N values of terrestrial and aquatic organic materials due to pre-analysis acid treatment methods.

by Chris Brodie

Rapid Communications in Mass Spectrometry. 25, 1089 - 1099.

Lead Author: Dr. Chris Brodie (Durham University, UK; Hong Kong University, Hong Kong)

Co-Authored with Dr. Tim Heaton (NIGL, UK); Prof. Melanie Leng (NIGL, UK) Christopher Kendrick (NIGL, UK); Dr. James Casford (Durham University, UK) and; Dr. Jeremy Lloyd (Durham University, UK)

ABSTRACT:
We investigate the effect of acid treatment methods on δ15N from a range of environmental organic... more ABSTRACT:
We investigate the effect of acid treatment methods on δ15N from a range of environmental organic materials in the context of the increased application of “dual-mode” isotope analysis (the simultaneous measurement of δ13C and δ15N from the same acid treated sample). Three common methods are compared; (i) untreated samples; (ii) acidification followed by sequential water rinse (rinse method); (iii) acidification in silver capsules (capsule method). The influence of capsule type (silver and tin) on δ15N is also independently assessed (as the capsule and rinse methods combust samples in different capsule; silver and tin respectively). We find significant differences in δ15N values between methods and the precision of any one method varies significantly between sample materials and above instrument precision (> 0.3 ‰). δ15N of untreated samples did not produce the most consistent data on all sample materials. In addition, the capsule type appears to influence the measured δ15N value of some materials, particularly those combusted only in silver capsules. We also compare the new δ15N data with previously published δ13C on the same materials. The response of δ13C and δ15N within and between methods and sample materials to acidification appears to be relatively disproportionate, which can influence environmental interpretation of the measured data. In addition, statistical methods used to estimate inorganic nitrogen are shown to be seriously flawed.

Keywords: acid treatment, capsule method, rinse method, acid method comparison, δ15N, inorganic nitrogen.

Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation techniques

by Chris Brodie

Chemical Geology. 282, 67 - 83.

Lead Author: Dr. Chris Brodie (Durham University, UK; Hong Kong University, Hong Kong)

Co-Authors: Prof. Melanie Leng (NIGL, UK), Dr. James Casford (Durham University, UK), Christopher Kendrick (NIGL, UK), Dr. Jeremy Lloyd (Durham University, UK), Dr. Zong Yongqiang (Hong Kong University, Hong Kong), Prof. Michael Bird (James Cook University, Australia).

ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the... more ABSTRACT:
This study is the first systematic comparison of the effect of acid treatment methods on the reliability of organic carbon [C] and nitrogen [N], and carbon isotope (δ13C) values on a range of terrestrial and aquatic, modern and geological environmental materials. We investigated the 3 most common methods; (i) acidification followed by sequential deionised water rinses (“rinse method”); (ii) acidification in silver capsules (“capsule method”); and (iii) acidification by exposure to an acid vapour (“fumigation method”). We also investigated the effect of sample size and capsule type (silver and tin) on C/N ratio and δ13C values. We find (i) %C, %N, C/N and δ13C showed significant within and between method variability; (ii) disproportionate and non-linear offsets of %C, %N and C/N values after acidification within and between methods and within and between sample materials; (iii) that alterations in %C did not necessarily manifest themselves in shifts in δ13C, and vice-versa; (iv) small (~ 90 μg C) sample sizes showed consistent overestimations and inaccuracies after acidification; (v) The effect of capsule type was not significant on most samples, but did show a notable effect on our aquatic materials, generally increasing %C and %N, and producing depleted δ13C values. These findings raise cause for concern on the interpretative nature of C/N ratios and their support for carbon isotope values. The comparability between laboratories (different preparation methods) and environmental settings (amount, type and nature of OM) are also likely to be problematic. We conclude that the response of C and N concentrations in organic matter to acid treatment in environmental materials is neither negligible nor systematic.

Keywords: δ13C; C/N ratio; Method comparison; Rinse method; Capsule method; Fumigation method; environmental reconstruction