Isotope ratio mass spectrometry as a tool for source inference in forensic science: A critical review

Simultaneous observation of 2H and 13C enrichment of methyl phosphonic acid via Orbitrap-IRMS with applications to nerve agent forensics

Quantification of the stable isotopes within a compound aids forensic investigations as it provides a fingerprint which can determine that compound's source substrates, synthetic route, and possible mechanisms of degradation. Previous stable isotope studies have explored 13C and 2H measurements of the sarin precursors methylphosphonic dichloride (DC) and methylphosphonic difluoride (DF) as forensic signatures. However, these measurements required different sample preparations and measurement techniques. Orbitrap isotope ratio mass spectrometry (Orbitrap-IRMS) is a developing technique which can characterize multiple stable isotopes simultaneously. Here, we apply Orbitrap-IRMS to simultaneously observe the 13C and 2H content of methylphosphonic acid (MPA), the hydrolysis product of DC and DF, which can be used as a proxy for the isotopic content of DC and DF. Our method requires 20 min analyses and consumes ≈60 nmol of sample, with precisions of ≈0.9 ‰ (13C) and ≈3.6 ‰ (2H). We apply our method to both commercially acquired MPA and MPA obtained from the hydrolysis of commercially acquired DC. We validate our methods via comparison to elemental-analyzer isotope ratio mass spectrometry (EA-IRMS). The combined 13C and 2H measurement creates a more robust forensic tool than either isotope individually. Our results demonstrate the viability of Orbitrap-IRMS for chemical forensic measurements.

Investigation of isotopic linkages between raw materials and black powder

The stable isotope analysis of black powder (BP) is of great significance for its comparison and source inference. Previous studies have verified the feasibility of distinguishing different BP samples through stable isotopes. However, the impact of raw materials and synthesis processes on the stable isotopes of BP remains unclear. On the one hand, the raw materials of BP are widely sourced, and whether stable isotopes can distinguish different source materials remains to be studied. On the other hand, the synthesis of BP involves the physical mixing of raw materials, and whether this process leads to isotope fractionation also needs further investigation. To address these problems, stable isotope ratios of 27 charcoals, 15 potassium nitrates, 6 self-made and 10 commercial BP samples were analyzed. The results showed that the stable isotope ratios can be utilized to distinguish charcoals and potassium nitrates from different manufacturers and batches. No significant differences in the nitrogen and oxygen stable isotope ratios between the self-made BP and its raw materials were observed, indicating that the physical mixing process does not induce significant fractionation of stable isotopes. However, the carbon stable isotope ratios of charcoal increased (within 2SD) after being synthesized into BP. Due to the utilization of additives and variations in the synthesis process, the correlation between the stable isotope ratios of commercial BP and its raw materials was complex. The findings of this study provide a scientific reference for tracing the source of BP.

Position-specific carbon stable isotope analysis of glyphosate: isotope fingerprinting of molecules within a mixture

Glyphosate [N-(phosphonomethyl) glycine] is a widely used herbicide and a molecule of interest in the environmental sciences, due to its global use in agriculture and its potential impact on ecosystems. This study presents the first position-specific carbon isotope (13C/12C) analyses of glyphosates from multiple sources. In contrast to traditional isotope ratio mass spectrometry (IRMS), position-specific analysis provides 13C/12C ratios at individual carbon atom positions within a molecule, rather than an average carbon isotope ratio across a mixture or a specific compound. In this work, glyphosate in commercial herbicides was analyzed with only minimal purification, using a nuclear magnetic resonance (NMR) spectroscopy method that detects 1H nuclei with bonds to either 13C or 12C, and isolates the signals of interest from other signals in the mixture. Results demonstrate that glyphosate from different sources can have significantly different intramolecular 13C/12C distributions, which were found to be spread over a wide range, with δ13C Vienna Peedee Belemnite (VPDB) values of -28.7 to -57.9‰. In each glyphosate, the carbon with a bond to the phosphorus atom was found to be depleted in 13C compared to the carbon at the C2 position, by 4 to 10‰. Aminomethylphosphonic acid (AMPA) was analyzed for method validation; AMPA contains only a single carbon position, so the 13C/12C results provided by the NMR method could be directly compared with traditional isotope ratio mass spectrometry. The glyphosate mixtures were also analyzed by IRMS to obtain their average 13C/12C ratios, for comparison with our position-specific results. This comparison revealed that the IRMS results significantly disguise the intramolecular isotope distribution. Finally, we introduce a 31P NMR method that can provide a position-specific 13C/12C ratio for carbon positions with a C-P chemical bond, and the results obtained by 1H and 31P for C3 carbon agree with one another within their analytical uncertainty. These analytical tools for position-specific carbon isotope analysis permit the isotopic fingerprinting of target molecules within a mixture, with potential applications in a range of fields, including the environmental sciences and chemical forensics.

Forensic application of isotope ratio mass spectrometry (IRMS) for human identification

Application of isotope ratio mass spectrometry (IRMS) to skeletal remains has become an important tool to investigate human behavior and history. Isotopic variations in collagen, enamel, and keratin reflect variations in an individual's diet and drinking water. Since food and water sources typically are geographically linked, isotope testing can assist in forensic identification by classifying remains to a likely geographic or population origin. If remains are commingled, differences in diet or geographic origin also can support their separation. The usefulness of IRMS in forensic science is dependent on the underlying quality and surety of the isotope test results; in other words, we need to understand their reliability in interpretations. To take ownership of isotopic data quality, we recommend asking a series of questions:Here, we use data collected during the buildout and accreditation of an isotope testing program at the Defense POW/MIA Accounting Agency (DPAA) to answer the above questions for the forensic application of IRMS for human identification. While our primary focus is on the preparation and analysis of bone collagen, the questions above should be considered whenever isotope testing is used in forensic casework. Whether the populations of interest are drugs or humans, olives or explosives, users need to evaluate their isotopic data and interpretations to ensure they are scientifically sound and legally defensible.

IRMS based evidence passes the test

At the two latest FIRMS (The Forensic Isotope Ratio Mass Spectrometry Network Ltd) conferences, presentations were made describing the status of IRMS based evidence in criminal proceedings [S. Doyle, T. Chau and J. Howa, IRMS based evidence passes the 'test' (aided by FIRMS) - an important milestone, in: 8th FIRMS Conference, 2022; J. Ehleringer, J. Howa and T. Chau, Stable isotope evidence in the U.S. courts, in: 7th FIRMS Conference, 2019]. One of those cases was of particular significance in that it established the admissibility of IRMS (isotope ratio mass spectrometry) based expert testimony having satisfied the US Federal Rule of Evidence (FRE)702 'Testimony by Expert Witnesses' in the State of Colorado. While specific to the State of Colorado and the particulars of the case, the admissibility of IRMS based evidence in other cases might be supported by such a ruling. This paper provides the detail of the process by which IRMS based evidence was found to be admissible and in so doing also provides practical guidance on how to satisfy FRE 702 and meet a Daubert challenge. It also highlights the role of approval by the FIRMS Network of both practitioners and their methods in support of admissibility [The FIRMS Network Ltd., FIRMS Approved Practitioners, [Online]. Available: https://www.forensic-isotopes.org/fafp.html [Accessed 11 May 2023].].

Linking ammonium nitrate-aluminum (AN-AL) post-blast residues to pre-blast explosive materials using isotope ratio and trace elemental analysis for source attribution

Forensic science practitioners are often called upon to attribute crimes using trace evidence, such as explosive remnants, with the ultimate goal of associating a crime with a suspect or suspects in order to prevent further attacks. The explosive charge is an attractive component for attribution in crimes involving explosives as there are limited pathways for acquisition. However, there is currently no capability to link an explosive charge to its source via post-blast trace residues using isotope ratios or trace elements. Here, we sought to determine if pre-blast attribution signatures are preserved after detonation and can be subsequently recovered and detected. A field study was conducted to recover samples of post-blast explosives from controlled detonations of ammonium nitrate-aluminum (AN-Al), which were then analyzed via isotope ratio mass spectrometry (IRMS) and inductively coupled plasma-mass spectrometry (ICP-MS) for quantitation and profiling of isotopes ratio and trace element signatures, respectively. Oxygen and nitrogen isotope ratios from AN-Al yielded some of the most promising results with considerable overlap within one standard deviation of the reference between the spreads of pre- and post-blast data. Trace element results from AN-Al support the findings in the isotope ratio data, with 26 elements detected in both pre- and post-blast samples, and several elements including B, Cd, Cr, Ni, Sn, V, and Zn showing considerable overlap. These preliminary results provide a proof-of-concept for the development of forensic examinations that can attribute signatures from post-blast debris to signatures in pre-blast explosive materials for use in future investigations.

State-of-the-Art Analytical Approaches for Illicit Drug Profiling in Forensic Investigations

In forensic chemistry, when investigating seized illicit drugs, the profiling or chemical fingerprinting of drugs is considered fundamental. This involves the identification, quantitation and categorization of drug samples into groups, providing investigative leads such as a common or different origin of seized samples. Further goals of drug profiling include the elucidation of synthetic pathways, identification of adulterants and impurities, as well as identification of a drug's geographic origin, specifically for plant-derived exhibits. The aim of this state-of-art-review is to present the traditional and advanced analytical approaches commonly followed by forensic chemists worldwide for illicit drug profiling. We discussed numerous methodologies for the physical and chemical profiling of organic and inorganic impurities found in illicit drug. Applications of powerful spectroscopic and chromatographic tools for illicit drug profiling including isotope-Ratio mass spectrometry (IRMS), gas chromatography-mass spectrometry (GC-MS), gas chromatography-isotope ratio mass spectrometry (GC-IRMS), ultra-high-performance liquid chromatography (UHPLC), thin layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS) and inductively coupled plasma-mass spectrometry (ICP-MS) were discussed. Altogether, the techniques covered in this paper to profile seized illicit drugs could aid forensic chemists in selecting and applying a suitable method to extract valuable profiling data.

Determination of stable nitrogen isotopic ratios of nitrate ions in ammonium nitrate

Ammonium nitrate (AN) is one of the most commonly used explosives in criminal cases. The comparison and source-tracing of AN is important for investigation of attribution and fingerprinting of an explosive used at different events. The stable isotope signature of AN is an important index for comparison and tracing. However, the characteristics of the stable nitrogen isotopic ratios of AN (δ¹⁵ N_NH4NO3 ) alone are not sufficient to achieve a fine comparison between different AN samples. To increase the comparison index and further improve the discriminability between stable nitrogen isotopic ratios of different ANs, a method of isolation and analysis of nitrate ions in AN was established using stable-isotope-ratio mass spectrometry (IRMS). The method was based on the principle that strong alkali react with AN to produce ammonia and nitrate. After the isolation, stable nitrogen isotopes of nitrate ions (δ¹⁵ N_NO3 ) were obtained using IRMS, and then the stable nitrogen isotopes of ammonium ions from AN (δ¹⁵ N_NH4 ) was calculated according to the principle of mass balance. The results show that the method is effective for the isolation of nitrate ions without notable isotope fractionation. The developed method was applied to analyze and discriminate AN samples from eight different cities in China. Three samples out of the initial eight AN samples with similar δ¹⁵ N_NH4NO3  values were further distinguished by their δ¹⁵ N_NH4 and δ¹⁵ N_NO3  values. The isolation and stable-nitrogen isotopic analysis method developed for nitrate ions in AN is simple and effective, thereby increasing the discriminability of the stable isotope ratios in AN.

Purification of ammonium nitrate via recrystallization for isotopic profiling using isotope ratio mass spectrometry

Stable-isotope analysis of ammonium nitrate (AN) plays an important role for comparing and tracing the sources of AN samples. Numerous studies have reported the application of isotope ratio mass spectrometry (IRMS) for the stable-isotope analysis of AN. However, in real cases, AN is often mixed with liquid hydrocarbons, organic explosives, wood flour, and sodium chloride. Therefore, the purification of AN samples prior to IRMS analysis is essential. Based on the different solubilities of AN at different temperatures, AN samples were purified by recrystallization. The results show that recrystallization can effectively purify AN, and the isotope fractionation effect caused by recrystallization increases the stable-isotope ratio (δ¹⁵N increased by 0.07-0.14‰, δ¹⁸O increased by 0.15-0.33‰, and δ²H increased by 4.61-18.16‰). The change of δ¹⁵N and δ¹⁸O were close to the standard deviation values, and did not affect the differentiation of AN. δ²H was deemed unsuitable for AN differentiation, owing to isotopic exchange during recrystallization. Eight AN samples from different cities and four AN samples produced in different years and batches from the same manufacturer in China were analyzed after recrystallization. Both groups of AN samples could be distinguished by combining the nitrogen and oxygen isotope ratios. Therefore, recrystallization can be used as a means of AN purification for the accurate determination of AN in ammonium nitrate fuel oil and explosive residues.

[Recent advances in stable isotope ratio analysis of common explosives]

炸药的深度比对与溯源对于爆炸案事件的侦破具有重大意义,以不同地域来源的原料或不同生产工艺生产的炸药,其组成元素的稳定同位素比值具有差异,因而稳定同位素比值可作为炸药深度比对与溯源的重要指标。稳定同位素比值质谱法(IRMS)作为一种高精度的稳定同位素比值测量手段,已逐渐发展成熟,与元素分析仪、气相色谱仪、液相色谱仪等仪器联用,在食品安全、环境保护、法庭科学等领域应用广泛。IRMS在炸药比对与溯源上亦发挥了重要作用,自1975年IRMS被应用于区分不同国家生产的三硝基甲苯(TNT)以来,IRMS已成功用于多种炸药的分析。但目前尚未见有文献系统地总结常见炸药的稳定同位素比值分析研究进展。该文介绍了稳定同位素比值分析的相关原理、仪器组成及特点,分别总结了硝酸铵、黑火药、TNT、太恩、黑索金等常见炸药的稳定同位素比值分析方法,汇总了文献报道的不同国家生产的硝酸铵、黑火药、TNT等炸药的稳定同位素比值。文章就不同炸药的稳定同位素比值差异、炸药生产、存储过程中相关因素对同位素比值的影响,爆炸前后稳定同位素比值的变化情况等内容进行了分析。本文还指出了目前炸药的稳定同位素比值分析研究中存在的问题,对可能的解决办法进行了讨论,对未来的发展方向提出了建议。

MASS SPECTROMETRY-BASED TECHNIQUES FOR DIRECT QUANTIFICATION OF HIGH IONIZATION ENERGY ELEMENTS IN SOLID MATERIALS-CHALLENGES AND PERSPECTIVES

The determination of nonmetals, first of all, the most electronegative ones-nitrogen, oxygen, fluorine, chlorine, and bromine, poses the highest challenge for element analysis. These elements are characterized by high reactivity, volatility, high ionization energy, and the absence of intensive spectral lines in the optical spectral range. Conventional techniques of their quantification include considerable "wet chemistry" stages so the application of these techniques for the solid sample is highly laborious and prone to uncontrollable uncertainties. Additionally, current development in material science and other areas requires the quantification of the elements at lower levels with good sensitivity. Owing to their robustness and flexibility, mass spectrometry techniques provide vast possibilities for the quantification, spatial and isotopic analysis, including the solutions for direct analysis of solids. The current review focuses on the application of major mass spectrometric techniques for the quantification of N, O, F, Cl, and Br in solid samples. The following techniques are mainly considered: thermal ionization mass spectrometry (TIMS), isotope-ratio MS (IRMS), secondary ion MS (SIMS), inductively coupled plasma MS (ICP-MS), and glow discharge MS (GDMS); as the most accessible and widely applied for the purpose. General ionization issues, advantages, limitations, and novel methodological solutions are discussed. © 2020 John Wiley & Sons Ltd.

NMR-based isotopic and isotopomic analysis

Molecules exist in different isotopic compositions and most of the processes, physical or chemical, in living systems cause selection between heavy and light isotopes. Thus, knowing the isotopic fractionation of the common atoms, such as H, C, N, O or S, at each step during a metabolic pathway allows the construction of a unique isotope profile that reflects its past history. Having access to the isotope abundance gives valuable clues about the (bio)chemical origin of biological or synthetic molecules. Whereas the isotope ratio measured by mass spectrometry provides a global isotope composition, quantitative NMR measures isotope ratios at individual positions within a molecule. We present here the requirements and the corresponding experimental strategies to use quantitative NMR for measuring intramolecular isotope profiles. After an introduction showing the historical evolution of NMR for measuring isotope ratios, the vocabulary and symbols - for describing the isotope content and quantifying its change - are defined. Then, the theoretical framework of very accurate quantitative NMR is presented as the principle of Isotope Ratio Measurement by NMR spectroscopy, including the practical aspects with nuclei other than ²H, that have been developed and employed to date. Lastly, the most relevant applications covering three issues, tackling counterfeiting, authentication, and forensic investigation, are presented, before giving some perspectives combining technical improvements and methodological approaches.

Forensic application of position-specific isotopic analysis of trinitrotoluene (TNT) by NMR to determine 13C and 15N intramolecular isotopic profiles

2,4,6-trinitrotoluene (TNT) is a molecule which is easily identified with current instrumental techniques but it is generally impossible to distinguish between sources of the same substance (TNT). To overcome this difficulty, we present a multi stable isotope approach using isotope ratio monitoring by mass spectrometry (irm-MS) and Nuclear Magnetic Resonance spectrometry (irm-NMR). In the one hand, irm-MS provides bulk isotopic composition at natural abundance in ¹³C and ¹⁵N. The range of variation between samples is rather small particularly for ¹³C. In the other hand, irm-¹³C NMR and irm-¹⁵N NMR enable the determination of positional intramolecular ¹³C/¹²C ratios (δ¹³C_i) and ¹⁵N/¹⁴N ratios (δ¹⁵N_i) with high precision that lead to larger variation between samples. The present work reports an application of the recent methodology using irm-¹⁵N NMR to determine position-specific ¹⁵N isotope content of TNT. The interest of this methodology is compared to irm-¹³C NMR and irm-MS (¹³C and ¹⁵N) in terms of TNT samples discrimination. Thanks to the use of irm-NMR the results show a unique isotopic fingerprint for each TNT which enable origin discrimination between the samples without ambiguity.

Stable isotope measurements to differentiate sources of monofluoroacetate in a blackmail case

RATIONALE

Stable isotope ratios can provide a 'fingerprint' to enable differentiation of sources of monofluoroacetate (MFA), hence providing a means to eliminate potential sources of MFA in a blackmail case involving the contamination of milk.

METHODS

The stable isotopic compositions (δ² H, δ¹³ C and δ¹⁸ O values) of a library of 43 samples of MFA were determined and multivariate models constructed to differentiate samples of different composition. The data from the MFA library were compared with those obtained from MFA extracted from contaminated milk powder (the case samples). The isotopic composition of the extracted samples was measured on dichloroaniline derivatives.

RESULTS

A wide range of values was found for δ² H, δ¹³ C and δ¹⁸ O of the MFA samples, much greater than the analytical repeatability between subsamples. Stable isotope data, therefore, provide a means of distinguishing samples of MFA. Of the 43 MFA samples tested, all but 6 could be eliminated as potential sources of the contamination, i.e. they had a distinctly different isotopic composition such that they must have had different histories and/or origins.

CONCLUSIONS

Stable isotope measurements of bulk and derivatized MFA provide an effective means of discriminating MFA samples. Three of the library samples that could not be differentiated from the case samples were directly connected to the suspect, and this evidence contributed to the suspect's admission of guilt.

Applying the principles of isotope analysis in plant and animal ecology to forensic science in the Americas

The heart of forensic science is application of the scientific method and analytical approaches to answer questions central to solving a crime: Who, What, When, Where, and How. Forensic practitioners use fundamentals of chemistry and physics to examine evidence and infer its origin. In this regard, ecological researchers have had a significant impact on forensic science through the development and application of a specialized measurement technique-isotope analysis-for examining evidence. Here, we review the utility of isotope analysis in forensic settings from an ecological perspective, concentrating on work from the Americas completed within the last three decades. Our primary focus is on combining plant and animal physiological models with isotope analyses for source inference. Examples of the forensic application of isotopes-including stable isotopes, radiogenic isotopes, and radioisotopes-span from cotton used in counterfeit bills to anthrax shipped through the U.S. Postal Service and from beer adulterated with cheap adjuncts to human remains discovered in shallow graves. Recent methodological developments and the generation of isotope landscapes, or isoscapes, for data interpretation promise that isotope analysis will be a useful tool in ecological and forensic studies for decades to come.

Multicomponent characterization and differentiation of flash bangers - Part II: Elemental profiling of plastic caps

This study builds on the multicomponent analysis strategy for flash bangers which was previously introduced and where a representative sample set has been collected of a certain type of flash bangers. To expand the forensic strategy, elemental analysis of the plastic caps which are present in these items was performed. Both x-ray fluorescence (XRF) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis was performed to explore the possibilities for differentiation. The inherent inhomogeneity of the plastics resulted in high variations, especially for LA-ICP-MS trace analysis. In addition, due to the lack of suitable reference materials the LA-ICP-MS results can only be used for qualitative comparisons. Although XRF is less sensitive it allows for semi-quantitative analysis and the effect of inhomogeneity is significantly reduced due to the larger sample areas. Therefore, XRF is the method of choice for elemental analysis of intact plastic caps. In this scenario initial differentiation based on visual examination is combined with elemental analysis to obtain the highest degree of discrimination. In post-explosive scenarios, using XRF is not as straightforward due the irregular shapes of the burned plastic cap residues and contamination by explosive residues. For the analysis of these post-explosive caps, LA-ICP-MS proved to be useful for characterization and differentiation. Overall, it was found that blue caps contain a considerable higher amount of elements than the white caps, mainly due to additives related to the coloring process. This limits differentiation for the flash bangers containing white caps. Therefore, isotope ratio mass spectrometry (IRMS) analysis was performed to increase the differentiation potential. Based on carbon and hydrogen isotope ratios additional sets could be distinguished, both for flash bangers containing white and blue caps, that otherwise have similar visual and elemental characteristics. With the elemental and isotopic analysis of the plastic caps, an analysis strategy has been introduced that is not based on the pyrotechnic charge and therefore provides a unique opportunity to perform characterization and differentiation of flash bangers in pre- and post-explosive casework.

Background survey of polyethylene in the Australian Capital Territory - A demonstration of variability in isotopic abundance values and their application to forensic casework

Plastics including adhesive tapes, cable ties, and packaging are common evidence types encountered in forensic investigations and casework. Traditional examination techniques such as Fourier Transform Infrared (FTIR) spectroscopy lack specificity and are unable to discern differences within the same polymer structures leaving the analyst with a generic identification. High quality manufacturing methods further amplify the limitations in detecting variability between samples. Isotope Ratio Mass Spectrometry (IRMS) has been shown to be a valuable technique in further discriminating plastics. Discrimination is achieved by analysing the relative abundances of stable isotopes within a sample, with differences detected in isotope ratios possibly attributed to the source of raw materials and fractionation during the manufacturing process. A survey of cling wraps and re-sealable zipper storage bags collected in the Australian Capital Territory was undertaken to assess the variability in carbon and hydrogen isotope ratios of different brands and samples. The results of this research are discussed, particularly with respect to within and between brand trends, and a case study is presented as an example of the value of including IRMS in a casework context.

Stable-carbon isotope ratios for sourcing the nerve-agent precursor methylphosphonic dichloride and its products

The ability to connect a chemical threat agent to a specific batch of a synthetic precursor can provide a fingerprint to contribute to effective forensic investigations. Stable isotope analysis can leverage intrinsic, natural isotopic variability within the molecules of a threat agent to unlock embedded chemical fingerprints in the material. Methylphosphonic dichloride (DC) is a chemical precursor to the nerve agent sarin. DC is converted to methylphosphonic difluoride (DF) as part of the sarin synthesis process. We used a suite of commercially available DC stocks to both evaluate the potential for δ¹³C analysis to be used as a fingerprinting tool in sarin-related investigations and to develop sample preparation techniques (using chemical hydrolysis) that can simplify isotopic analysis of DC and its synthetic products. We demonstrate that natural isotopic variability in DC results in at least three distinct, isotope-resolved clusters within the thirteen stocks we analyzed. Isotopic variability in the carbon feedstock (i.e., methanol) used for DC synthesis is likely inherited by the DC samples we measured. We demonstrate that the hydrolysis of DC and DF to methylphosphonic acid (MPA) can be used as a preparative step for isotopic analysis because the reaction does not impart a significant isotopic fractionation. MPA is more chemically stable, less toxic, and easier to handle than DC or DF. Further, the hydrolysis method we demonstrated can be applied to a suite of other precursors or to sarin itself, thereby providing a potentially valuable forensic tool.

TATP isotope ratios as influenced by worldwide acetone variation

Isotope ratio analysis has been shown to discriminate samples of forensic interest and to link many synthesized and natural materials to their precursors when traditional chemical and physical analyses cannot. Successful application of stable isotope analysis to chemicals of interest requires a background of likely variations in stable isotope ratios; often, this background population can be generated from analysis of possible precursors and the relationships of stable isotopes of precursor(s) to product(s), which may depend on synthesis techniques. Here we measured the carbon (¹³C/¹²C) and hydrogen (²H/¹H) isotope ratios of the oft-illicitly manufactured explosive triacetone triperoxide, TATP, and one of its precursors, acetone. As acetone is the sole source of carbon and hydrogen to TATP, a survey of acetone from 12 countries was conducted to explore the breadth of ¹³C/¹²C and ²H/¹H variation in the precursor, and therefore, its product. Carbon and hydrogen isotope ratios were measured using continuous flow isotope ratio mass spectrometry (IRMS) techniques. We observed greater ranges in both C and H isotope ratios of acetone than previously published; we also found that country-of-purchase was a large contributing factor to the observed variation, larger than acetone grade and brand. Following clandestine production methods, we observed that the stable isotope ratios of TATP retained the stable isotope signatures of acetone used in synthesis. We confirmed the robustness of TATP carbon isotope ratios to both recrystallization and time-dependent sublimation, important considerations when faced with the task of practical sampling of potential unexploded TATP from a crime scene.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

Isotope (δ13C, δ15N, δ2H) diet-tissue discrimination in African grey parrot Psittacus erithacus: implications for forensic studies

Diet-tissue isotopic relationships established under controlled conditions are informative for determining the dietary sources and geographic provenance of organisms. We analysed δ¹³C, δ¹⁵N, and non-exchangeable δ²H values of captive African grey parrot Psittacus erithacus feathers grown on a fixed mixed-diet and borehole water. Diet-feather Δ¹³C and Δ¹⁵N discrimination values were +3.8 ± 0.3 ‰ and +6.3 ± 0.7 ‰ respectively; significantly greater than expected. Non-exchangeable δ²H feather values (-62.4 ± 6.4 ‰) were more negative than water (-26.1 ± 2.5 ‰) offered during feather growth. There was no positive relationship between the δ¹³C and δ¹⁵N values of the samples along each feather with the associated samples of food offered, or the feather non-exchangeable hydrogen isotope values with δ²H values of water, emphasising the complex processes involved in carbohydrate, protein, and income water routing to feather growth. Understanding the isotopic relationship between diet and feathers may provide greater clarity in the use of stable isotopes in feathers as a tool in determining origins of captive and wild-caught African grey parrots, a species that is widespread in aviculture and faces significant threats to wild populations. We suggest that these isotopic results, determined even in controlled laboratory conditions, be used with caution.

Identification of the Species of Origin for Meat Products by Rapid Evaporative Ionization Mass Spectrometry

Increasingly abundant food fraud cases have brought food authenticity and safety into major focus. This study presents a fast and effective way to identify meat products using rapid evaporative ionization mass spectrometry (REIMS). The experimental setup was demonstrated to be able to record a mass spectrometric profile of meat specimens in a time frame of <5 s. A multivariate statistical algorithm was developed and successfully tested for the identification of animal tissue with different anatomical origin, breed, and species with 100% accuracy at species and 97% accuracy at breed level. Detection of the presence of meat originating from a different species (horse, cattle, and venison) has also been demonstrated with high accuracy using mixed patties with a 5% detection limit. REIMS technology was found to be a promising tool in food safety applications providing a reliable and simple method for the rapid characterization of food products.

A novel high-temperature combustion interface for compound-specific stable isotope analysis of carbon and nitrogen via high-performance liquid chromatography/isotope ratio mass spectrometry

RATIONALE

In aqueous samples compound-specific stable isotope analysis (CSIA) plays an important role. No direct method (without sample preparation) for stable nitrogen isotope analysis (δ(15) N SIA) of non-volatile compounds is known yet. The development of a novel HPLC/IRMS interface based on high-temperature combustion (HTC) for both δ(13) C and δ(15) N CSIA and its proof of principle are described in this study.

METHODS

To hyphenate high-performance liquid chromatography (HPLC) with isotope ratio mass spectrometry (IRMS) a modified high-temperature combustion total organic carbon analyzer (HTC TOC) was used. A system to handle a continuously large amount of water (three-step drying system), favorable carrier and reaction gas mix and flow, an efficient high-temperature-based oxidation and subsequent reduction system and a collimated beam transfer system were the main requirements to achieve the necessary performance.

RESULTS

The proof of principle with caffeine solutions of the system succeeded. In this initial testing, both δ(13) C and δ(15) N values of tested compounds were determined with precision and trueness of ≤0.5 ‰. Further tests resulted in lower working limit values of 3.5 μgC for δ(13) C SIA and 20 μgN for δ(15) N SIA, considering an accuracy of ±0.5 ‰ as acceptable.

CONCLUSIONS

The development of a novel HPLC/IRMS interface resulted in the first system reported to be suitable for both δ(13) C and δ(15) N direct CSIA of non-volatile compounds. This highly efficient system will probably open up new possibilities in SIA-based research fields. Copyright © 2016 John Wiley & Sons, Ltd.

Enhanced forensic discrimination of pollutants by position-specific isotope analysis using isotope ratio monitoring by (13)C nuclear magnetic resonance spectrometry

In forensic environmental investigations the main issue concerns the inference of the original source of the pollutant for determining the liable party. Isotope measurements in geochemistry, combined with complimentary techniques for contaminant identification, have contributed significantly to source determination at polluted sites. In this work we have determined the intramolecular (13)C profiles of several molecules well-known as pollutants. By giving additional analytical parameters, position-specific isotope analysis performed by isotope ratio monitoring by (13)C nuclear magnetic resonance (irm-(13)C NMR) spectrometry gives new information to help in answering the major question: what is the origin of the detected contaminant? We have shown that isotope profiling of the core of a molecule reveals both the raw materials and the process used in its manufacture. It also can reveal processes occurring between the contamination site 'source' and the sampling site. Thus, irm-(13)C NMR is shown to be a very good complement to compound-specific isotope analysis currently performed by mass spectrometry for assessing polluted sites involving substantial spills of pollutant.