Elemental Analyzer/isotope Ratio Mass Spectrometry Research Articles

A closer look into the nitrogen blank in elemental analyser/isotope ratio mass spectrometry measurements.

One important limitation for the precise measurement of minute amounts of nitrogen (N) in solid samples by elemental analyser/isotope ratio mass spectrometry (EA/IRMS) is the accurate determination of the analyser blank value. This study was performed to identify different sources, amounts and isotopic composition of N blanks in EA/IRMS in order to identify measures for minimising the effect of the N blank on N isotopic data quality. Different types of autosamplers, with and without zero-blank functionality, were tested by analysing different amounts of substances of varying isotopic composition by EA/IRMS. Using zero-blank autosamplers reduces the atmospheric N2 blank from 60nmol to between 4 and 5nmol depending on the autosampler type. This blank is derived from atmospheric N2 leaking into the elemental analyser, trapped in the sample tin capsules or contained in the oxygen added for combustion. Another source of blank is the reaction tube. As the sources of the blank differ, the isotopic composition of the blank is very variable. In addition, cross-contamination from previous samples may contribute up to 3.3nmol N. For precise measurements of minute amounts of N in solid samples, reduction of the N blank is the most promising strategy. Correcting for the remaining N blank is only meaningful if the sample isotopic composition is very different from that of the N blank, because the precise determination of the isotopic composition of the N blank is not possible.

Measurement of the 15N/14N ratio of phenylalanine in fermentation matrix by isotope ratio mass spectrometry.

To determine the origin of 15N-labeled phenylalanine in microbial metabolic flux analysis using 15N as a tracer, a method for measuring phenylalanine δ15N using HPLC coupled with elemental analysis-isotope ratio mass spectrometry (EA-IRMS) was developed. The original source of the 15N-labeled phenylalanine was determined using this new method that consists of three steps: optimization of the HPLC conditions, evaluation of the isotope fractionation effects, and evaluation of the effect of pre-processing on the phenylalanine nitrogen stable isotope. In addition, the use of a 15N-labeled inorganic nitrogen source, rather than 15N-labeled amino acids, was explored using this method. The method described here can also be applied to the analysis of metabolic flux.

Stable Carbon Isotope Composition of the Lipids in Natural Ophiocordyceps sinensis from Major Habitats in China and Its Substitutes.

Ophiocordyceps sinensis is one rare medicinal fungus produced in the Qinghai-Tibetan Plateau. Its quality and price varies hugely with different habitat, and its numerous substitutes have sprung up in functional food markets. This paper aims to discriminate the geographic origin of wild O. sinensis and its substitutes via element analyzer–isotope ratio mass spectrometry and gas chromatography–isotope ratio mass spectrometry. The δ13C values of major fatty acids in the lipids of O. sinensis are characterized unanimously by the variation relation C18:0 < C18:2 ≈ C16:0 < C18:1, while their fluctuation intervals are notably different between those of neutral and polar lipids. The comparative analysis of the δ13C ratios of major fatty acids in lipids of O. sinensis suggests that the δ13C patterns may be sensitive potential indicators to discriminate its geographical origin. The δ13C values of individual major fatty acids of lipids from the cultivated stromata of Cordyceps militaris (SCM), the fermented mycelia of Hirsurella sinensis (FMH) and Paecilomyces epiali (FMP) range from −31.2‰ to −29.7‰, −16.9‰ to −14.3‰, and −26.5‰ to −23.9‰, respectively. Their δ13C pattern of individual major fatty acids may be used as a potential indicator to discriminate the products of natural O. sinensis and its substitutes.

Isotopic homogeneity throughout the skin in small cetaceans.

Isotope ratios from skin samples have been widely used to study cetacean trophic ecology. Usually, isotopic skin uniformity has been assumed, despite the heterogeneity of this tissue. This study aims to investigate (1) regional isotopic variation within the skin in cetaceans, and (2) isotopic variation among internal tissues. Stable carbon (δ13 C values) and nitrogen (δ15 N values) isotope ratios were measured in 11 skin positions in 10 common dolphins (Delphinus delphis) and 9 striped dolphins (Stenella coeruleoalba). In addition, the isotope ratios in the muscle, liver and kidney of both species were determined and compared with those from the skin and from all tissues combined. The signatures were determined by means of elemental analyser/isotope ratio mass spectrometry (EA/IRMS). In both species, no differences between isotope ratios of the skin positions were found. Moreover, the isotope ratios of skin were similar to those of muscle. In contrast, liver and kidney showed higher isotope ratios than muscle and skin. Isotopic homogeneity within the skin suggests that the isotope ratios of a sample from a specific skin position can be considered representative of the ratios from the entire skin tissue in dolphins. This conclusion validates the results of previous stable isotope analyses in dolphins that used skin samples as representative of the whole skin tissue. Isotopic similarities or dissimilarities among tissues should be considered when analysing different tissues and comparing results from the same or different species.

Differentiation of Fractionated Components of Lard from Other Animal Fats Using Different Analytical Techniques

A study was conducted to differentiate fractionated components of lard namely lard olein (LO) and lard stearin (LS) from other common animal fats. Lard fractions and animal fats were analyzed using differential scanning calorimetry (DSC), elemental analyzer–isotope ratio mass spectrometry (EA-IRMS), gas chromatography mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). Overlay of FTIR spectra did not help to pinpoint any characteristic feature to distinguish either LO or LS from other animal fats, but overlay of DSC cooling curves helped a successful discrimination. The determination of δ13C from EA-IRMS showed that the values corresponding to the fractionated components of lard were significantly (p<0.05) different from those of the other common animal fats. GC-MS analysis showed that direct comparison of overall fatty acid data was not able to discriminate LO and LS from other animal fats, but the application of principal component analysis (PCA) to fatty acid data helped a successful discrimination.

Validation of GC-IRMS techniques for δ13C and δ2H CSIA of organophosphorus compounds and their potential for studying the mode of hydrolysis in the environment.

Compound-specific stable isotope analysis (CSIA) is among the most promising tools for studying the fate of organic pollutants in the environment. However, the feasibility of multidimensional CSIA was limited by the availability of a robust method for precise isotope analysis of heteroatom-bearing organic compounds. We developed a method for δ 13C and δ 2H analysis of eight organophosphorus compounds (OPs) with different chemical properties. In particular, we aimed to compare high-temperature conversion (HTC) and chromium-based HTC (Cr/HTC) units to explore the limitations of hydrogen isotope analysis of heteroatom-bearing compounds. Analysis of the amount dependency of the isotope values (linearity analysis) of OPs indicated that the formation of HCl was a significant isotope fractionation process leading to inaccurate δ 2H analysis in HTC. In the case of nonchlorinated OPs, by-product formation of HCN, H2S, or PH3 in HTC was observed but did not affect the dynamic range of reproducible isotope values above the limit of detection. No hydrogen-containing by-products were found in the Cr/HTC process by use of ion trap mass spectrometry analysis. The accuracy of gas chromatography-isotope ratio mass spectrometry was validated in comparison with elemental analyzer-isotope ratio mass spectrometry. Dual-isotope fractionation yielded Λ values of 0 ± 0 at pH 7, 7 ± 1 at pH 9, and 30 ± 6 at pH 12, indicating the potential of 2D CSIA to characterize the hydrolysis mechanisms of OPs. This is the first report on the combination of δ 2H and δ 13C isotope analysis of OPs, and this is the first study providing a systematic evaluation of HTC and Cr/HTC for hydrogen isotope analysis using OPs as target compounds. Graphical Abstract Comparison of δ2H measurement of non-chlorinated and chlorinated OPs via GC-Cr/HTC-IRMS and GC-HTC-IRMS system.

IRMS to study a common cocaine cutting agent: phenacetin.

Phenacetin is a pharmaceutical closely related to acetaminophen that has been banned in France for a long time due to its nephritic and carcinogenic adverse effects. It frequently appears in cocaine seizures as a cutting agent. Following both sanitary and intelligence motivations, this molecule was chosen for this study, and stable isotopes seemed to be the most appropriate tool. A total of 228 seized samples were collected over a 6-year period, and 8 standards of known origin were purchased. They were submitted to gas chromatography (GC) or elemental analysis - isotope ratio mass spectrometry (EA-IRMS) measurements, depending on their complexity. Stable isotope ratios of carbon, hydrogen, and nitrogen for a part of the sample set, were acquired. The isotopic values of phenacetin standards acquired from various providers located worldwide are quite spread, which indicates that stable isotopes could be used to discriminate manufacturers. However, the measured values of most of the seized samples are concentrated in a narrow range, tending to demonstrate that phenacetin is smuggled from a single source or similar ones. Consequently, stable isotopes could only be used to exclude that several samples come from a common source. Copyright © 2016 John Wiley & Sons, Ltd.

Bulk δ15 N measurements of organic-rich rock samples by elemental analyzer/isotope ratio mass spectrometry with enhanced oxidation ability.

Elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) has been widely used for nitrogen isotope ratio determination in various organic and inorganic samples. However, the extent of the redox reaction in the EA reaction tube can greatly affect the accuracy and precision of measurements, especially in the case of complex geological samples. It is therefore necessary to determine the appropriate reaction conditions to reach a high recovery of nitrogen by complete combustion or thermal decomposition and quantitative reduction. The conventional Dumas dual-inlet method was used to determine the bulk nitrogen isotope composition of SGR-1 (an organic-rich standard sample), which then was analyzed by EA/IRMS under different EA reaction conditions to study the influence of the redox environment on the δ15 N measurements. The measured data together with the results reported by previous researchers were used to evaluate the effectiveness of the nitrogen extraction for organic-rich rock samples. Our results demonstrated that with the Dumas dual-inlet method more oxidizing agent (CuO) addition to SGR-1 would yield a higher nitrogen content of 0.91% than the recommended content (0.81%) although a δ15 N value of 17.39±0.09‰ was consistent with the recommended value by USGS. Using EA/IRMS, when more O2 was injected in the reaction tube, a high nitrogen content (0.92±0.01%) and a δ15 N value (17.43±0.17‰) close to that of the Dumas dual-inlet method were obtained. The addition of V2 O5 or CuO in a continuous-flow system of EA/IRMS could not effectively enable the complete combustion of SGR-1. When measuring the nitrogen isotope composition of organic-rich rock sample dominated by reduced substances with EA/IRMS, greater O2 injection will enable more complete combustion to obtain reliable nitrogen yields compared with the addition of V2 O5 or CuO. Copyright © 2016 John Wiley & Sons, Ltd.

Carbon and nitrogen stable isotopic offsets between diet and hair/feces in captive chimpanzees.

Estimation of the stable isotopic offsets between tissue and diet is important for dietary reconstructions. Although stable isotopic studies of chimpanzees (Pan troglodytes) are increasing, the isotopic offsets in chimpanzees have never been studied. In this study, the carbon and nitrogen stable isotopic offset values in hair and feces were measured for 13 captive chimpanzees for the first time. All consumed food items and quantities were recorded for each individual for 1week. Food samples were typically collected three times, hair was collected 3weeks after the experimental week, and feces were collected ad libitum during the experimental week. The stable carbon and nitrogen isotope ratios were measured using elemental analyzer-isotope ratio mass spectrometry (EA-IRMS). As the results of Monte Carlo analysis, the estimated carbon and nitrogen offsets between the hair and diet were +3.0 to +3.9‰ and +2.8 to +3.7‰, respectively, for the 95% confidence intervals (CIs). The 95% CIs of the carbon and nitrogen offset values between the feces and diet were -1.6 to 0.0‰ and +1.2 to +2.7‰, respectively. These offset values are generally consistent with those of the other primate species reported in previous studies. However, potential variations in the offset values due to dietary and physiological factors should be studied in detail in the future. Copyright © 2016 John Wiley & Sons, Ltd.

Sulfur and strontium isotopic study of epithermal mineralization: A case study from the SE Afar Rift, Djibouti

Epithermal mineralization was recently described in synrift volcanic rocks from the SE Afar Rift in Djibouti. To infer fluid sources in this system, coupled sulfur and strontium isotopic analyses were performed on mineralized samples from hydrothermal veins and stockwork zones. Mineralization includes gypsum and chalcedony, and/or quartz±carbonate containing gold and sulfides. Sulfur isotopic compositions of sulfides and sulfates were determined using Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC ICPMS); Laser Ablation MC ICPMS; and Continuous Flow Elemental Analyzer-Isotope Ratio Mass Spectrometry while strontium isotopes were determined by Thermal Ionisation Mass Spectrometry (TIMS) methods. Sulfur isotopic composition of sulfides (mainly pyrite) varies from −9.2 to +6.6‰. These values are classically reported for hydrothermal sulfides resulting from the mixing of variable S sources such as seawater sulfate and magmatic source. In addition, individual pyrite grains within the same sample show both positive and negative δ34S values suggesting multi-phase mineralization processes. Coupled sulfur and strontium isotopic compositions of seven sulfate samples hosted in (i) gypsum mound, (ii) evaporites, (iii) stockwork veins in sediments or in volcanic rocks were also investigated to characterize the sources of Sr and S. The δ34S values of the sulfate ranged from −0.8 to +14.3‰ while the 87Sr/86Sr ranged from 0.70389 to 0.70639 consistent with variable mixing ratios of Sr and S derived from volcanic sources and seawater-derived sulfate. This study shows that, although precious-metal deposition is related to low-sulfidation epithermal environment, both acidic fluid of magmatic and saline origins contributed to the hydrothermal system in the SE Afar Rift.

Improved Discrimination for Brassica Vegetables Treated with Agricultural Fertilizers Using a Combined Chemometric Approach.

Multielement and stable isotope (δ(13)C, δ(15)N, δ(2)H, δ(18)O, (207)Pb/(206)Pb, and (208)Pb/(206)Pb) analyses were combined to provide a new chemometric approach to improve the discrimination between organic and conventional Brassica vegetable production. Different combinations of organic and conventional fertilizer treatments were used to demonstrate this authentication approach using Brassica chinensis planted in experimental test pots. Stable isotope analyses (δ(15)N and δ(13)C) of B. chinensis using elemental analyzer-isotope ratio mass spectrometry easily distinguished organic and chemical fertilizer treatments. However, for low-level application fertilizer treatments, this dual isotope approach became indistinguishable over time. Using a chemometric approach (combined isotope and elemental approach), organic and chemical fertilizer mixes and low-level applications of synthetic and organic fertilizers were detectable in B. chinensis and their associated soils, improving the detection limit beyond the capacity of individual isotopes or elemental characterization. LDA shows strong promise as an improved method to discriminate genuine organic Brassica vegetables from produce treated with chemical fertilizers and could be used as a robust test for organic produce authentication.

Compound-Specific Isotope Analysis of Amino Acid Labeling with Stable Isotope Nitrogen (15N) in Higher Plants

Individual free amino acid δ15N values in plant tissue reflect the metabolic pathways involved in their biosynthesis and catabolism and could thus aid understanding of environmental stress and anthropogenic effects on plant metabolism. In this study, compound-specific nitrogen isotope analysis of amino acid by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) was carried out to determine individual free amino acid δ15N values. High correlations were observed between the δ15N values obtained by GC-C-IRMS and elemental analyzer-isotope ratio mass spectrometry (EA-IRMS) determinations, and the mean precision measured was better than 1 ‰. Cation-exchange chromatography was employed to purify the sample, and the difference between prior to and following passage through the resin was within 1 ‰. The amino acid δ15N values of plant leave samples following incubation in 15N-nitrate at different time points were determined. A typical foliar free amino acid 15N-enrichment pattern was found, and glutamine was the most rapidly labeled amino acid; other amino acids derived from the GS-GOGAT cycle were also enriched. The pyruvate family amino acids were labeled less quickly followed by the aromatic amino acids. This study highlighted that amino acid metabolism pathways had a major effect on the δ15N values. With the known amino acid metabolism pathways and δ15N values determined by the presented method, the influence of various external factors on the metabolic cycling of amino acid can be understood well.

Effects of HCl pretreatment, drying, and storage on the stable isotope ratios of soil and sediment samples.

Stable isotope (δ(13) C, δ(15) N, δ(34) S values) analysis has become increasingly important for tracing contaminant sources in environments. Pretreatment of environmental samples allows accurate analysis of stable isotope ratios. The pretreatment of a sample and its subsequent preservation could either contaminate or create experimental artifacts affecting the validity of the resulting C/N ratios and the elemental isotopic contents of a sample. The effects of acid pretreatment (0.1, 0.5, 1, 2, 5, 13 M HCl) and exposure period (2, 6, 12, 24, and 48 h) on the stable isotopic ratios of marine sediment (MS), river sediment (RS) and terrestrial soil (TS) samples were evaluated. The effects of storage temperatures (-80, -20 and 2°C), storage duration (1 week, 1 to 12 months) and washing steps (1, 2, 3, 5, 7 or 12 times) on the stable isotopic ratios were also considered. The %C, %N and %S, as well as the δ(13) C, δ(15) N, and δ(34) S values, of each sample were measured using continuous flow Elemental Analyzer/Isotope Ratio Mass Spectrometry (EA/IRMS). The HCl treatment was applicable for δ(13) C analysis. However, the acid concentration and duration of exposure that brought about total removal of carbonate for the three sample types varied; e.g. the TS sample required stronger acid and a shorter exposure time. Storage time also had an effect: the δ(13) C values were lower and the δ(15) N and δ(34) S values higher after storage for 300 days. HCl pretreatment effectively eliminates carbonates and thereby helps δ(13) C analysis of the organic fraction. HCl pretreatment is not recommended for δ(15) N and δ(34) S analysis. Freeze-drying of samples is recommended rather than oven drying. A temperature-dependent change in the isotopic ratios of long-term stored samples was observed during this study; therefore, relatively short-term storage (-80°C) of freeze-dried samples is preferable. Copyright © 2016 John Wiley & Sons, Ltd.

Towards Incorporating Insect Isotope Analysis Using Cavity Ring-Down Spectroscopy into Area-Wide Insect Pest Management Programs

Measurement of natural stable isotope signatures of insects has proven to be a useful method in determining their natal origin, feeding strategies and mating behavior, and has spawned a new discipline of insect isotope forensics. However the complexity of measuring isotope signatures using elemental analysis-isotope ratio mass-spectrometry (EA-IRMS) has encountered significant technical barriers, which together with costs, have hindered the advancement and wide spread adoption of this potentially useful approach. In the last decade simpler technologies to measure stable isotope ratios in samples based on laser spectroscopy have been developed. We foresee that these instruments will fuel the advancement and adoption of insect isotope forensics into pest management programs because they are easy to use, more affordable, and complement existing marking tools. However prior to the adoption of these new technologies it is necessary to test their fitness for purpose and explore their limitations. In this paper we set out to test the suitability of using combustion module-cavity ring-down spectroscopy (CM-CRDS) for measuring isotope ratios in an entomological context, covering marking of insects, mating behavior and dietary assessment. We carried out a series of experiments to compare the isotope measurements made with the CM-CRDS with the traditional method of EA-IRMS. Initially we compared measurements of carbon isotope values of a variety of common diet components used in insect rearing, which covered a wide range of carbon isotope values. There was good agreement in the isotope values obtained, using the CM-CRDS and the EA-IRMS with similar accuracy and precision. Secondly we compared the 2 methods to measure carbon isotope values of the common cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) samples, and again there was good agreement in the values obtained. Thirdly we tested whether the CM-CRDS could be used to determine the paternity of spermataphores, based on the differential isotope signatures of the paternal and maternal moths, as a result of differences in their rearing diets. The CM-CRDS proved to be fit for the purpose of measuring isotope values in the spermataphores of common cutworm and suggested that the CM-CRDS technology would be suitable for these isotope based mating studies in moths if the spermatophores were of sufficient mass. Finally we explored a number of the issues surrounding CM-CRDS and isotope technologies in general, e.g., logistical considerations, economics of operation, sample size, etc. We conclude that CM-CRDS is a suitable instrument for measuring stable isotope carbon signatures in moths, and most probably other sufficiently large insects and that CM-CRDS could be easily used in both operational and research contexts.

Differentiation of partial acylglycerols derived from different animal fats by EA-IRMS and GCMS techniques

A study was carried out to compare partial acylglycerols of lard with those of chicken fat, beef fat and mutton fat using Gas Chromatography Mass Spectrometry (GC-MS) and Elemental Analysis–Isotope Ratio Mass Spectrometry (EA-IRMS). Mono- (MAG) and di-(DAG) acylglycerols of animal fats were prepared according to a chemical glycerolysis method and isolated using column chromatography. The fatty acid composition and δ 13 C carbon isotope ratio of MAG and DAG derived from individual animal fat were determined separately to establish their identity characteristics. The results showed that the δ 13 C values of MAG and DAG of lard were significantly different from those of MAG and DAG derived from chicken fat, beef fat and mutton fat. According to the loading plots based on a principle component analysis (PCA), fatty acids namely stearic, oleic and linoleic were the most discriminating parameters to distinctly identify MAG and DAG derived from different animal fats. This demonstrated that the EA-IRMS and the PCA of fatty acid data have considerable potential for discriminating MAG and DAG derived from lard from other animal fats for Halal authentication purposes.

Stable Isotope Ratios Combined with Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope Analysis to Identify the Dried Shark Fins

The authenticity of dried shark fins was identified using stable carbon and nitrogen isotopic compositions, chemical structure, and morphology characterization by means of element analyzer-isotope ratio mass spectrometry (EA-IRMS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis, and scanning electron microscope (SEM) characterization of samples. The results indicated that real dried shark fins, fake dried shark fins, and artificial dried shark fins could be easily distinguished from each other. δ13C values of real dried shark fins, fake dried shark fins, and artificial dried shark fins were −14.231 ± 1.204‰, −17.247 ± 0.621‰, and −14.561 ± 1.016‰, respectively, and highly significant (P < 0.01) within real dried shark fins and fake dried shark fins. On the other hand, δ15N values of artificial dried shark fins (6.860 ± 0.519‰) and real dried shark fins (13.501 ± 2.421‰) presented significant differences (P < 0.01). Considering the obvious differences of these samples with ATR-FTIR and SEM analysis, the combination of IRMS with ATR-FTIR and SEM technique has the advantage over traditional identification method to be relatively good in accuracy and applicability. Thus, these techniques could potentially be useful for dried shark fin identification.

Diet-to-female and female-to-pup isotopic discrimination in South American sea lions.

The use of accurate, species-specific diet-tissue discrimination factors is a critical requirement when applying stable isotope mixing models to predict consumer diet composition. Thus, diet-to-female and female-to-pup isotopic discrimination factors in several tissues for both captive and wild South American sea lions were estimated to provide appropriate values for quantifying feeding preferences at different timescales in the wild populations of this species. Stable carbon and nitrogen isotope ratios in the blood components of two female-pup pairs and females' prey muscle from captive individuals were determined by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) to calculate the respective isotopic discrimination factors. The same analysis was carried out in both blood components, and skin and hair tissues for eight female-pup pairs from wild individuals. Mean diet-to-female Δ(13) C and Δ(15) N values were higher than the female-to-pup ones. Pup tissues were more (15) N-enriched than their mothers but (13) C-depleted in serum and plasma tissues. In most of the tissue comparisons, we found differences in both Δ(15) N and Δ(13) C values, supporting tissue-specific discrimination. We found no differences between captive and wild female-to-pup discrimination factors either in Δ(13) C or Δ(15) N values of blood components. Only the stable isotope ratios in pup blood are good proxies of the individual lactating females. Thus, we suggest that blood components are more appropriate to quantify the feeding habits of wild individuals of this species. Furthermore, because female-to-pup discrimination factors for blood components did not differ between captive and wild individuals, we suggest that results for captive experiments can be extrapolated to wild South American sea lion populations.

Improved accuracy and precision in δ15NAIR measurements of explosives, urea, and inorganic nitrates by elemental analyzer/isotope ratio mass spectrometry using thermal decomposition

Elemental analyzer systems generate N(2) and CO(2) for elemental composition and isotope ratio measurements. As quantitative conversion of nitrogen in some materials (i.e., nitrate salts and nitro-organic compounds) is difficult, this study tests a recently published method - thermal decomposition without the addition of O(2) - for the analysis of these materials. Elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) was used to compare the traditional combustion method (CM) and the thermal decomposition method (TDM), where additional O(2) is eliminated from the reaction. The comparisons used organic and inorganic materials with oxidized and/or reduced nitrogen and included ureas, nitrate salts, ammonium sulfate, nitro esters, and nitramines. Previous TDM applications were limited to nitrate salts and ammonium sulfate. The measurement precision and accuracy were compared to determine the effectiveness of converting materials containing different fractions of oxidized nitrogen into N(2). The δ(13) C(VPDB) values were not meaningfully different when measured via CM or TDM, allowing for the analysis of multiple elements in one sample. For materials containing oxidized nitrogen, (15) N measurements made using thermal decomposition were more precise than those made using combustion. The precision was similar between the methods for materials containing reduced nitrogen. The %N values were closer to theoretical when measured by TDM than by CM. The δ(15) N(AIR) values of purchased nitrate salts and ureas were nearer to the known values when analyzed using thermal decomposition than using combustion. The thermal decomposition method addresses insufficient recovery of nitrogen during elemental analysis in a variety of organic and inorganic materials. Its implementation requires relatively few changes to the elemental analyzer. Using TDM, it is possible to directly calibrate certain organic materials to international nitrate isotope reference materials without off-line preparation.

Multi-Element (C, N, H, O) Stable Isotope Ratio Analysis for Determining the Geographical Origin of Pure Milk from Different Regions

In order to identify the geographical origin of pure milk, different proteins and milk water were extracted from pure milk originated from Australia and New Zealand, Germany and France, the USA, and China. Then, δ 13C and δ 15N values of the extracted proteins and δ 2H and δ 18O values of milk water were determined by element analyzer-isotope ratio mass spectrometry (EA-IRMS). The results indicated that pure milk from these regions could be potentially discriminated by using analyte δ 13C, δ 15N, δ 2H, and δ 18O. The P value analysis of them was highly significant (P < 0.01) considering the origins. 3D distribution of δ 13C, δ 15N, δ 2H, and δ 18O can also clearly present regional concentration phenomena according to the regions of pure milk. Therefore, it can be concluded that δ 13C, δ 15N, δ 2H, and δ 18O analysis could potentially be rapid and routine for origin discrimination of pure milk.

Development of methodology for the determination of carbon isotope ratios using gas chromatography/combustion/isotope ratio mass spectrometry and applications in the biodegradation of phenolic brominated flame retardants and their degradation products.

Compound-specific stable carbon isotope analysis of phenolic brominated flame retardants (BFRs) and bisphenol A (BPA) has proven informative to discriminate their source and fate apportionment in the environment. However, because these compounds contain highly polar functional groups and exist as complex mixtures in environment matrices, derivatization is a necessary step, which adds additional non-analyte carbon atoms for analyses and may alter the original stable carbon isotope ratio. It is, therefore, imperative to gain an insight into the relationship between the δ(13) C values of the BFRs and BPA derivatives and those of underivatized BFRs and BPA. The δ(13) C values of BFRs and BPA N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) derivatives were measured by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). The δ(13) C values of the BSTFA reagent and the standard underivatized BFRs and BPA were determined using elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). The experimentally obtained δ(13) C values for BFRs and BPA derivatives were then compared with the theoretically calculated values. The derivatization process introduces no isotopic fractionation for BFRs and BPA (the average difference between the theoretically calculated and experimentally obtained δ(13) C values was 0.06 ± 0.15‰, within the precision limits of the GC/C/IRMS measurements). Therefore, the δ(13) C values for the original underivatized BFRs and BPA were computed through a mass balance equation. This work offers a novel tool to research the biotic or abiotic transformation processes of BFRs and BPA in the environment and will offer a perspective for the identification of the environmental source and fate of these organic compounds.