Isotope ratio data

Not including error correlations where significant (say >0.3) in isotope-ratio data tables ... 

Coplen, T. B. (1996) New guidelines for reporting stable hydrogen, carbon, and oxygen isotope ratio data. Geochimica et Cosmochimica Acta 60, 3359. 

Baxter, M.J. and Gale, N.H. (1998). Testing for multivariate normality via univariate tests a case study using lead isotope ratio data. Journal of Applied Statistics 25 671-683. 

A test of the hypothesis that the linear trends in Figures 10-12 are due to mixing comes from comparisons with oxygen isotopes. It has been conventional wisdom that Mg does not correlate in detail with O excesses in primitive chondrite components, including CAIs. However, combining the new highly precise MC-ICPMS data with isotope ratio data for the... 

The above empirical equation can be derived theoretically, and the deviation of the experimentally observed Ce isotope ratio data from Curve I illustrates the extent to which the tropospheric atmosphere is not instantly and uniformly mixed this enables us to follow the eastward movement of the nuclear debris around the world... 

Natural carbonate minerals do not form from pure solutions where the only components are water, calcium, and the carbonic acid system species. Because of the general phenomenon known as coprecipitation, at least trace amounts of all components present in the solution from which a carbonate mineral forms can be incorporated into the solid. Natural carbonates contain such coprecipitates in concentrations ranging from trace (e.g., heavy metals), to minor (e.g., Sr), to major (e.g., Mg). When the concentration of the coprecipitate reaches major (>1%) concentrations, it can significantly alter the chemical properties of the carbonate mineral, such as its solubility. The most important example of this mineral property in marine sediments is the magnesian calcites, which commonly contain in excess of 12 mole % Mg. The fact that natural carbonate minerals contain coprecipitates whose concentrations reflect the composition of the solution and conditions, such as temperature, under which their formation took place, means that there is potentially a large amount of information which can be obtained from the study of carbonate mineral composition. This type of information allied with stable isotope ratio data, which are influenced by many of the same environmental factors, has become a major area of study in carbonate geochemistry. 

The calcium isotope ratio data of Table IIA were obtained using a triple filament thermal ionization procedure ( ) that was modified to permit operation of the ionizing filament at a higher temperature... 

MOORE Stable Isotope Measurements Table lllB. Comparative for RNAA and 21 Isotope Ratio Data IRMS ... 

Figure 7 Isotopic patterns measured in bulk samples of SiC extracted from the Murchison meteorite. Isotopic ratios are relative to the reference isotope plotted as a solid circle and are normalized to the solar isotopic ratios. Data are from Lewis et al. (1994) (Kr and Xe), Podosek et al. (2003) (Sr), Prombo et al. (1993) (Ba), Richter et al. (1993)...

With natural gas being a mixture of such structurally simple compounds, options available for correlation purposes are limited. Gas chromatography provides an indication of the distribution of the components present in the namral gas sample from which the ratio of methane/C2+ fraction can be determined. This is measure of the wetness of the gas and in certain cases can provide a measure of the maturity of the gas. The ratio needs to be combined with carbon and isotope ratio data to obtain the most useful information. A gas can be dominated by methane and, from the chromatogram alone, it is impossible to determine whether this is biogenic gas or a high maturity gas. As a result of thousands of... 

If the origin of the material is not known, the specific activity should be either measured or calculated by using isotopic ratio data. 

There are also a few limitations of GC-MS. The problems encountered previously by several investigators have been the poor precision and accuracy of isotope ratio data, the memory effect during the sequential analysis of samples with different isotope ratios, and the lack of suitable chelating agents. In addition, the contributions of the different isotopes of C, N, S, etc., present in the chelating agent need to be accounted for, particularly when studying the enrichments in different samples followed by tracer administration (intravenous or oral). 

Natural abundance isotope ratio data are generally quoted as delta values, 5. Delta values can be calculated using the following formula ... 

Pierrini et al. [108] discuss issues surrounding the interpretation of isotope ratio data and present a continuous likelihood ratio approach for the evaluation of data generated from the analysis of the plastic explosive Semtex (RDX/PETN). The authors highlighted the need for large international isotope ratio databases in order for this approach to work. 

Figure 3.7 Mg isotope ratio data for terrestrial mantle-rocks and minerals, whole-rock chondrites, pallasite olivines, Martian meteorites, and lunar basalts and breccia. Error bars represent the external reproducibility in 2SE (= 2a/v/n, where n is the number of measurements per sample). Not considering the dunite DTSl and the harzburgite PCC-1 (with 32% serpentine [15]), which are both likely affected by processes occurring after their emplacement within the Earth s crust, the average (5 Mg of the BSE is —0.54 + 0.04 (2SE), which overlaps with that of average chondrites (—0.52 + 0.04), pallasites (—0.54 + 0.04), Mars (—0.57 + 0.02), and the Moon (—0.51 0.03), showing that the stable Mg isotopic composition of the inner solar system (dotted lines, <5 Mg = —0.54) is homogeneous to within 0.05%o.

The corabination of an inductively coupled plasma ion source and a magnetic sector-based mass spectrometer equipped with a multi-collector (MC) array [multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS)] offers precise and reliable isotope ratio data for many solid elements. In fact, MC-ICP-MS provides data, the trueness (accuracy) and precision of which is similar to, or, in some cases, even superior to, that achieved by thermal ionization mass spectrometry (TIMS), considered the benchmark technique for isotope ratio measurements of most solid elements [1], The basic strength of ICP-MS lies in the ion source, which achieves extremely high ionization efficiency for almost all elements [2, 3]. Consequently, MC-ICP-MS is likely to become the method of choice for many geochemists, because it is a versatile, user-friendly, and efficient method for the isotopic analysis of trace elements [4-8], The ICP ion source also accepts dry sample aerosols generated by laser ablation [9-16], The combination of laser ablation (LA) with ICP-MS is now widely accepted as a sensitive analytical tool for the elemental and isotopic analysis of solid samples. 

In all these applications, isotope ratio data are produced, which are interpreted on an absolute or relative basis and which have an impact on our daily life, whether this is in science (e.g., age of an artifact), in society (e.g., provenance of food), or in public safety (e.g., neutron shielding in nuclear power plants). To ensure that these data are reliable and accurate, some specific requirements have to be fulfilled. The main requirement is that all these measurement results are comparable, which means that the corresponding results can be compared and differences between the measurement results can be used to draw further conclusions. This is only possible if the measurement results are traceable to the same reference [25]. This in turn can only be realized by applying isotopic reference materials (IRMs) for correction for bias and for validation of the analytical procedure. Whereas in earlier days only experts in mass spectrometry were able to deliver reproducible isotope ratio data, nowadays many laboratories, some of which may even have never been involved with mass spectrometry before, produce isotope ratio data using inductively coupled plasma mass spectrometry (ICP-MS). Especially for such users, IRMs are indispensable to permit proper method validation and reliable results. The rapid development and the broad availability of ICP-MS instrumentation have also led to an expansion of the research area and new elements are under investigation for their isotopic variations. In this context, all users require IRMs to correct for instrumental mass discrimination or at least to allow isotope ratio data to be related to a commonly accepted basis. 

Description The isotopic composition is characterized via isotope amount ratios or isotope amount fractions. These data have been obtained from measurements which have been corrected for all bias occurring in mass spectrometry. In terms of isotope ratio data, one can often read about absolute isotope ratio data or absolute measurements. Here it is meant that the measurements leading to isotope ratio data are a best estimate for the true value. From a metrological point of view, all published isotope ratio data should be corrected for all bias and should be accompanied by an uncertainty budget. Isotope amount fractions and atomic weights should only be calculated from fiilly corrected isotope amount ratios. Anything else is observed data only. Thus, isotope amount fractions and molar masses are always true or absolute data [35]. 

Today, we face two opposite trends. Triggered by the rapid development of ICP-MS, the number of published isotope ratio data increased rapidly. This rapid development also caused an increasing number of wrong isotope ratio data to be published, such as the Sr isotope ratio data for ginseng by Choi et al. [82]. The extremely low Sr/ Sr data published by Choi et al. fall in a range that does not even exist today in terrestrial materials, as was demonstrated by Rosner [83]. The provision of suitable IRMs and their subsequent application can help to avoid such failings. 

Therefore, scientists should contact the national metrology institutes such as NIST and BAM or international institutions such as IRMM when new materials are needed. The production of IRMs by these institutes ensures that the requirements for an IRM are fulfilled. Only with IRMs is the comparability of isotope ratio data enabled. 

---