Isotope Ratio Mass Spectrometry Data Research Articles

PSLBI-17 Total sulfur amino acid requirements across the canine life cycle in Labrador Retrievers using the indicator amino acid oxidation (IAAO) technique

Abstract Methionine and cysteine are the principal sulfur-containing amino acids that are incorporated into proteins, although homocysteine and taurine also have important physiological roles in canines. As limited studies have been conducted for total sulfur-containing amino acids (TSAA) requirements across the canine life cycle, our objective was to determine the minimum requirements (MR) for TSAA at 4 life stages using the indicator amino acid oxidation (IAAO) technique. Labrador Retrievers (n = 24) were used in feeding studies to evaluate the changing requirements of TSAA as dogs mature: 6 puppies aged 10 to 14 wk, 6 puppies >14 wk to 9 mos, 6 adults 2 to 5 yr (yr), and 6 seniors > 8yr. Following a 2-d adaptation to a TSAA-adequate basal diet (TSAA = 1.12% dry matter), dogs underwent individual IAAO studies. In brief, all dogs were randomly fed one of six test diets with varying levels of TSAA ranging from deficient to sufficient (final TSAA content in experimental diets were 0.41, 0.46, 0.51, 0.98, 1.05, and 1.12% dry matter, with indispensable amino acids formulated at 1.6x NRC values). The test diet was divided into 13 equal meals; at the 5th meal, a tracer amino acid was included (a bolus L-[1-13C] phenylalanine based on body weight was first given, followed by [1-13C] Phe doses every 30 spanning 4 h). Breath samples were collected via a respiration mask every 30 min. Total CO2 production was determined via indirect calorimetry and production of 13CO2 at each dose was measured by enrichment of 13C in breath samples via isotope ratio mass spectrometry (IRMS). Results for IRMS data were converted to atom percent excess (APE) and analyzed using segmented linear regression. The Four Rivers mean and population requirements for TSAA were estimated to be 1.55 ± 0.069 g/1,000 kcal (mean ± 2 SD) for puppies 10 to 14 wk, 1.53 ± 0.21 g/1,000 kcal (mean ± 2 SD) for puppies 14 wk to 9 mo, 1.4 ± 0.30 g/1000 kcal (mean ± 2 SD) for adults 2 to 5 yr, and 1.27 ± 0.23 g/1,000 kcal (mean ± 2 SD) for seniors. These results may contribute to the formulation of diets that meet the age-appropriate requirements of TSAA for large-breed dogs at all life stages.

PSLBI-18 Isoleucine requirements of young adult and senior Labrador retrievers

Abstract Age-appropriate diets that meet the unique nutritional needs of aging are in greater demand as senior dogs represent an increasing percentage of the pet population. Studies targeting the specific amino acid requirements of the aging canine are important because they may inform dietary formulations for this specific life stage. In this study, the indicator amino acid oxidation (IAAO) technique was used to determine the minimum requirements for isoleucine (Iso) in young adult and senior Labrador retrievers. After 2-d adaptation to Iso-adequate basal diet (Iso = 0.608% dry matter), dogs underwent individual IAOO studies. In brief, all dogs were randomly fed one of six test diets with varying levels of isoleucine ranging from deficient to sufficient (final Iso content in experimental diets were 0.244, 0.285, 0.326, 0.532, 0.57 and 0.608% dry matter). Test diet was divided into 13 equal meals; at the 5th meal, a tracer amino acid was supplied (a bolus L-[1-13C] phenylalanine based on body weight was first given, followed by [1-13C] Phe doses every 30 min spanning a 4 h period), and breath samples were collected via respiration mask every 30 min. CO2 production was determined via indirect calorimetry and production of 13CO2 at each dose was measured by enrichment of 13C in breath samples via isotope ratio mass spectrometry (IRMS). Results for IRMS data were converted to atom percent excess (APE) and analyzed using segmented linear regression. The Four Rivers mean and population requirements for isoleucine were 898 ± 71 mg/1,000 kcal ME (mean ± 2 SD) for young adults and 885 ± 91 mg/1,000 kcal ME (mean ± 2 SD) in senior dogs, which is slightly greater than the National Research Council’s minimum requirement. As the pet food industry offers more specialized diets for aging canines, updating the amino acid requirements for such animals is increasingly important.

Exploratory data analysis (EDA) machine learning approaches for ocean world analog mass spectrometry

Many upcoming and proposed missions to ocean worlds such as Europa, Enceladus, and Titan aim to evaluate their habitability and the existence of potential life on these moons. These missions will suffer from communication challenges and technology limitations. We review and investigate the applicability of data science and unsupervised machine learning (ML) techniques on isotope ratio mass spectrometry data (IRMS) from volatile laboratory analogs of Europa and Enceladus seawaters as a case study for development of new strategies for icy ocean world missions. Our driving science goal is to determine whether the mass spectra of volatile gases could contain information about the composition of the seawater and potential biosignatures. We implement data science and ML techniques to investigate what inherent information the spectra contain and determine whether a data science pipeline could be designed to quickly analyze data from future ocean worlds missions. In this study, we focus on the exploratory data analysis (EDA) step in the analytics pipeline. This is a crucial unsupervised learning step that allows us to understand the data in depth before subsequent steps such as predictive/supervised learning. EDA identifies and characterizes recurring patterns, significant correlation structure, and helps determine which variables are redundant and which contribute to significant variation in the lower dimensional space. In addition, EDA helps to identify irregularities such as outliers that might be due to poor data quality. We compared dimensionality reduction methods Uniform Manifold Approximation and Projection (UMAP) and Principal Component Analysis (PCA) for transforming our data from a high-dimensional space to a lower dimension, and we compared clustering algorithms for identifying data-driven groups (“clusters”) in the ocean worlds analog IRMS data and mapping these clusters to experimental conditions such as seawater composition and CO2 concentration. Such data analysis and characterization efforts are the first steps toward the longer-term science autonomy goal where similar automated ML tools could be used onboard a spacecraft to prioritize data transmissions for bandwidth-limited outer Solar System missions.

A laboratory-scale greenhouse for spectroscopic monitoring of plants and associated gas-phase isotopic fractionation

The ability to monitor isotopic fractionation in terrestrial ecosystems is a challenge due to the presence of interacting variables. A laboratory-scale apparatus for controlled experiments could serve as a useful platform to deconvolute the variables that affect isotopic fractionation. Such a device could offer a powerful means to understand fractionation of carbon stocks in terrestrial ecosystems and to probe the effects of photosynthesis or interactions between the soil and plants on carbon fractionation. To this end, an enclosed and artificially-lit benchtop soil and plant chamber was constructed and equipped to monitor atmospheric isotopic composition. Fourier-transform infrared (FTIR) spectroscopy was employed for isotopic sensing since it enables in-situ measurements. The validity of FTIR for isotopic ratio determination was confirmed by comparing FTIR and isotope ratio mass spectrometry data for a series of CO2 gas samples with known quantities of 13C and 12C. The greenhouse chamber was also equipped with an optically-based trace gas analyzer capable of continuously tracking CO2, CH4, and H2O concentrations and a residual gas analyzer mass spectrometer. Reflectance spectroscopy was also incorporated by way of sealed fiber optic feed-throughs coupled to a spectro-radiometer, for quantifying changes in leaf spectra induced by various environmental stressors. The resulting greenhouse chamber can be a useful tool for determining the effects of atmospheric trace gases on plant morphology and physiology as a function of concentration and isotopic composition. Microecosystems can be examined under controlled laboratory conditions and a wide variety of plant species can be accommodated. The bench-scale greenhouse should prove useful in assessing the impact of environmental variables and in guiding the design of field experiments.

Physical model for multi-point normalization of dual-inlet isotope ratio mass spectrometry data.

A simple model is presented for multi-point normalization of dual-inlet isotope ratio mass spectrometry (DI-IRMS) data. The model incorporates the scale contraction coefficient and the normalized working reference gas isotope delta value as its two physical parameters. The model allows the full use of isotope measurement data and outputs the normalized sample isotope delta value along with the mentioned parameters. The model reduces to the expected linear behavior on application to a natural range CO2 isotopic composition sample, under typically observed scale contraction levels. Next, DI-IRMS measurements of the NIST CO2 gas isotopic reference materials (RMs) 8562, 8563, and 8564 are used to construct a three-point linear calibration, spanning 40‰ for the [Formula: see text] and 20‰ for the [Formula: see text] raw data. Accuracy of the regression at the 0.009‰ level for [Formula: see text] and 0.01‰ for [Formula: see text] is observed for the three NIST RMs. The model derived scale contraction term is found to be a more accurate measure of cross-contamination in contrast to its end of day measurements by the enriched sample method. The constructed multi-point normalization model is next used to assign [Formula: see text] and [Formula: see text] isotope delta values on the Vienna PeeDee Belmnite-CO2 (VPDB-CO2) scale, for pure CO2 gas samples in the natural isotopic range. A Monte Carlo analysis of the uncertainty, including estimates for the normalization step, is provided to assist future multi-point normalization with more than three reference points.

Determination of Sucrose Additives and Geographical Origin Markers in Honey Using Isotope Ratio Mass Spectrometry and Ultra High Performance Liquid Chromatography – Evoparative Light Scattering Detection

Abstract Honey can easily be adulterated with various cheaper sweeteners for higher commercial profits. Commonly used adulterants include high fructose maize syrup and refined cane sugar, which origin is C4 plants. Isotope ratio mass spectrometry (IRMS) can be used to determine the adulteration of honey with C4 plants. A significant δ13C value difference between honey and its protein provide valuable information of honey authenticity. The IRMS analysis of honey and its proteins and ultra high performance liquid chromatography – evoparative light scattering detection analysis for adulterated honey were performed to assess honey authenticity and origin. Principal component analysis of the obtained IRMS data was performed in order to determine discrimination between groups and for visualisation of observations. The results showed that isotope ratio values in combination with principal component analysis could be useful for determination of adulterant and discrimination of honey of different geographical origins. The chromatography results show ascending increase of the deliberately added sucrose, but do not fully recover the expected value.

Combination of stable isotope ratio data and chromatographic impurity signatures as a comprehensive concept for the profiling of highly prevalent synthetic cannabinoids and their precursors

In this study, we utilized elemental analyser (EA) and gas-chromatography (GC) isotope ratio mass spectrometry (IRMS) and ultra-high-performance liquid chromatography coupled to mass spectrometry (UHPLC-MS) in a comprehensive profiling approach assessing the chromatographic impurity signatures and δ13C and δ15N isotope ratios of synthetic cannabinoids from police seizures and internet test purchases. Main target of this study was the highly prevalent synthetic cannabinoid MDMB-CHMICA (methyl (2S)-2-([1-(cyclohexylmethyl)-1H-indol-3-yl]formamido)-3,3-dimethylbutaoate). Overall, 61 powder and 118 herbal blend (also called “Spice-Products”) samples were analysed using both analytical techniques and evaluated in a joint model to link samples from a common source. As a key finding, three agglomerates of Spice-product samples with similar dates of purchase were identified in the IRMS data, possibly representing larger shipments of MDMB-CHMICA, each produced with the same precursor material, successively delivered to the European market. The three agglomerates were refined into multiple sub-clusters based on the impurity profiling data, each representing an individual synthesis batch. One of the agglomerates identified in the IRMS data was found to consist two groups of four sub-clusters, respectively, with majorly different impurity profiles, demonstrating the necessity for both analytical techniques to extract the maximum amount of information from a limited sample pool. Additionally, 31 samples containing the recently surfaced synthetic cannabinoid Cumyl-PeGaClone (5-pentyl-2-(2-phenylpropan-2-yl)-2,5-dihydro-1H-pyrido[4,3-b]indol-1-one) were analysed for their and δ13C and δ15N isotope ratios to put the isotopic data recorded for MDMB-CHMNICA in a more global perspective. Three building blocks of precursor chemicals (indole, tert-leucine, cumylamine) potentially used for the synthesis of the two named synthetic cannabinoids were acquired from different global vendors and measured for their δ13C and δ15N isotope ratios to better understand variations in the isotopic composition of the synthetic cannabinoids and to trace their origin.

Fast IRMS screening of pseudoendogenous steroids in doping analyses.

The detection of the abuse of pseudoendogenous steroids (testosterone and/or its precursors) is currently based, when possible, on the application of the steroid module of the World Anti-Doping Agency (WADA), athlete biological passport (ABP), implemented through the global database, ADAMS. When a suspicious sample is detected, the confirmation by isotope ratio mass spectrometry (IRMS) is required. It is well known that this confirmation procedure is time consuming and expensive and can be only applied on a reduced number of samples. In previous studies we have demonstrated that the longitudinal evaluation of the IRMS data is able to detect positive samples that otherwise will be evaluated as negative, improving the efficacy of the fight against doping in sport. This would require the analysis of a much larger volume of samples by IRMS. The aim of the present work is to describe an IRMS screening method allowing to increase the throughput of samples that can be analyzed by IRMS. The detection efficacy of the method is compared with the confirmation method in use, and to assess its robustness and applicability, all the samples of a major cycling stage competition were analyzed, with the agreement of the testing authority, under routine conditions and response times. The results obtained permit to conclude that the IRMS screening method here proposed has adequate selectivity and produces results that overlap with the already validated method currently in use permitting to analyze a much higher volume of samples even during a major event without compromising the detection capacity. Copyright © 2017 John Wiley & Sons, Ltd.

Increasing the linear dynamic range in LC-MS: is it valid to use a less abundant isotopologue?

Liquid chromatography-mass spectrometry (LC-MS) has quickly become the analytical method of choice in forensic toxicology laboratories due to its ability to detect a very wide range of compounds in a single analysis. One of the major limitations of LC-MS however, is a relatively limited linear dynamic range for quantitation. A new approach to combating this problem is to use the [+1 M+H]+ isotope mass peak for quantitation, thereby reducing saturation at the detector and extending the linear range. This is particularly useful in full-scan applications, such as quadrupole-time-of-flight (QTOF) mass spectrometry, where the isotopic mass peaks are acquired as a matter of course. Due to the variation in abundance of naturally occurring isotopes for common elements, especially 13 C, this technique has the potential to lead to additional quantitative error. Through a review of published isotope ratio mass spectrometry data, we have assessed this potential for error and found that it is likely to be less than 2% and unlikely to be more than 4%, although this may not apply to compounds containing high numbers of nitrogen or sulphur atoms. This additional potential error must be considered before using this technique as it may not be appropriate for all applications. We have deemed it fit for purpose for our application and demonstrate the applicability of this technique to a quantitative LC-TOF method. © 2017 Commonwealth of Australia. Drug Testing and Analysis © 2017 John Wiley & Sons, Ltd.

Intranasal delivery of Natesto® testosterone gel and its effects on doping markers.

The laboratory profile of intranasal testosterone gel has not been previously reported from an anti-doping perspective. Because intranasal testosterone gel is newly available as a commercial product, we sought to examine the laboratory parameters following administration of this formulation, with particular attention to anti-doping guidelines. Five healthy and active male subjects were administered testosterone intranasal gel three times daily for four weeks, using a pattern of five consecutive days on, two days off. Urine was collected after each five-day round of drug administration and analyzed using a full steroid screen and isotope ratio mass spectrometry (IRMS). Windows of detection for elevated testosterone/epitestosterone (T/E) and other steroid ratios, World Anti-Doping Agency (WADA) athlete biological passport (ABP) findings, and IRMS results were analyzed in this study. In the 0-24 h window post-administration, 70% of samples were flagged with a suspicious steroid profile and 85% were flagged as atypical passport findings according to the WADA ABP steroid module. In the 24-48 h window, 0% of samples displayed suspicious steroid profiles while 40% resulted in atypical passport findings. IRMS testing confirmed the presence of exogenous testosterone in 90% and 40% of samples in the 0-24 h and 24-48 h windows post-administration, respectively. Additionally, IRMS data were analyzed to determine commonalities in the population changes in δ13 C values of testosterone, androsterone, etiocholanolone, 5αAdiol, and 5βAdiol. Though no discernible metabolic trend of the route of administration was identified, we discovered that intranasal gel testosterone is detectable using conventional anti-doping tests. Copyright © 2016 John Wiley & Sons, Ltd.

Longitudinal evaluation of the isotope ratio mass spectrometric data: towards the 'isotopic module' of the athlete biological passport?

The detection of the abuse of pseudo-endogenous steroids (testosterone and/or its precursors) is currently based on the application of the steroid module of the World Anti-Doping Agency (WADA) Athletes' Biological Passport (ABP), implemented through ADAMS. Diagnostic metabolites are monitored for every athlete and statistically evaluated with a predictive Bayesian approach. In the case of suspicious samples, the data of the ABP are confirmed and the isotope ratio mass spectrometry (IRMS) test is activated. We have previously demonstrated that IRMS enables confirmation of the non-endogenous origin of pseudo-endogenous steroids in otherwise non-suspicious samples, after a longitudinal evaluation of the ABP, even after the inclusion of additional long-term diagnostic hydroxylated metabolites, and that the delta values of the parameters obtained during the IRMS confirmation process presented much less variability compared to the parameters of the ABP. The aim of the present work is to evaluate the application of the same methodology used for the evaluation of the ABP, on the delta values of the pseudo-endogenous steroids monitored. The effectiveness of the proposed model has been assessed on samples obtained after controlled administrations of oral androstenedione and transdermal testosterone. The results support the conclusion that, if applied, the longitudinal evaluation of the IRMS data allows the detection of positive samples that otherwise will be reported as atypical findings (ATF), improving the efficacy of the fight against doping in sport. This approach, by narrowing the individual acceptable range, could possibly improve the detection of the intake of preparations of synthetic origin with delta values close to or overlapping those of endogenously produced steroids. Copyright © 2016 John Wiley & Sons, Ltd.

The Potential of Isotope Ratio Mass Spectrometry (IRMS) and Gas Chromatography-IRMS Analysis of Triacetone Triperoxide in Forensic Explosives Investigations.

Studying links between triacetone triperoxide (TATP) samples from crime scenes and suspects can assist in criminal investigations. Isotope ratio mass spectrometry (IRMS) and gas chromatography (GC)-IRMS were used to measure the isotopic compositions of TATP and its precursors acetone and hydrogen peroxide. In total, 31 TATP samples were synthesized with different raw material combinations and reaction conditions. For carbon, a good differentiation and a linear relationship were observed for acetone-TATP combinations. The extent of negative (δ(13) C) fractionation depended on the reaction yield. Limited enrichment was observed for the hydrogen isotope (δ(2) H) values of the TATP samples probably due to a constant exchange of hydrogen atoms in aqueous solution. For oxygen (δ(18) O), the small isotopic range and excess of water in hydrogen peroxide resulted in poor differentiation. GC-IRMS and IRMS data were comparable except for one TATP sample prepared with high acid concentration demonstrating the potential of compound-specific isotope analysis. Carbon IRMS has practical use in forensic TATP investigations.

Determination of geographical origin of distillers dried grains and solubles using isotope ratio mass spectrometry

In recent years distillers dried grains and solubles (DDGS), co-products of the bio-ethanol and beverages industries, have become globally traded commodity for the animal feed sector. As such it is becoming increasingly important to be able to trace the geographical origin of commodities in case of a contamination incident or authenticity issue arise. In this study, 137 DDGS samples from a range of different geographical origins (China, USA, Canada and European Union) were collected and analyzed. Isotope ratio mass spectrometry (IRMS) was used to analyze the DDGS for 2H/1H, 13C/12C, 15N/14N, 18O/16O and 34S/32S isotope ratios which can vary depending on geographical origin and processing. Univariate and multivariate statistical techniques were employed to investigate the feasibility of using the IRMS data to determine botanical and geographical origin of the DDGS. The results indicated that this commodity could be differentiated according to their place of origin by the analysis of stable isotopes of hydrogen, carbon, nitrogen and oxygen but not with sulfur. By adding data to the models produced in this study, potentially an isotope databank could be set up for traceability procedures for DDGS, similar to the one established already for wine which will help in feed and food security issues arising worldwide.

The use of δ13C isotope ratio mass spectrometry for methamphetamine profiling: Comparison of ephedrine and pseudoephedrine-based samples to P2P-based samples

Differentiating methamphetamine samples produced from ephedrine and pseudoephedrine from phenyl-2-propanone precursors is critical for assigning synthetic route information for methamphetamine profiling. The use of isotope ratio mass spectrometry data is now a key component for tracking precursor information. Recent carbon (δ13C) isotope results from the analysis of numerous methamphetamine samples show clear differentiation for ephedrine and pseudoephedrine-produced samples compared to P2P-produced samples. The carbon isotope differences were confirmed from synthetic route precursor studies.

Organic impurities, stable isotopes, or both: A comparison of instrumental and pattern recognition techniques for the profiling of 3,4-methylenedioxymethamphetamine

In this study, we precisely synthesised 61 3,4-methylenedioxymethamphetamine hydrochloride (MDMA.HCl) samples. The synthetic route, reaction conditions, and batch of starting material used were carefully controlled in order to facilitate the assessment of the sample linkage abilities of: (1) GCMS organic impurity profiling using different sets of target impurities recommended from the published literature, and (2) stable isotope ratio mass spectrometry (IRMS) for δ13C, δ15N, δ2H, and δ18O-values. For GCMS analysis, we utilised the extraction parameters, instrumental conditions, and data analysis techniques recently published. In addition to this, we analysed all MDMA.HCl samples by IRMS for their 13C, 15N, 2H, and 18O isotopic composition. The resulting data sets were subjected to hierarchical cluster analysis, principal component analysis, and discriminant analysis to identify which type of measurement (i.e.GCMS, IRMS, or both), which set of target impurities for GCMS, and which data pre-treatment method offers meaningful discrimination of the samples according to batch of starting material used, synthetic route used, or both. For our data set, discriminant analysis using a combination of the IRMS data and GCMS data (‘Van Deursen’ impurities pre-treated with the fourth root method) provided the most accurate discrimination of the MDMA.HCl samples. Principal component analysis had the second highest success rate, and hierarchical cluster analysis had only limited success at producing meaningful discrimination of the samples into their known groupings.

Simultaneous Identification and δ13C Classification of Drugs Using GC with Concurrent Single Quadrupole and Isotope Ratio Mass Spectrometers*

In this study, δ¹³C values of six cocaine samples were identified and classified using a single quadrupole mass spectrometer and an isotope ratio mass spectrometry (IRMS) as simultaneous gas chromatography detectors. Our instrument modification is simple to use and is useful (i) when the sample is of limited size or can only be injected once, (ii) to help identify peaks in a complicated IRMS chromatogram, and (iii) to help differentiate very simple systems when impurity profiling is not possible. The EI-MS confirmed the identity of cocaine in each sample. The IRMS data distinguished 12 of the 15 possible pair-wise comparisons at the 95% CL. Three samples could not be differentiated by their δ¹³C ratios for cocaine. ANOVA demonstrated that the measurement variance was consistently larger than the sample variance. As the δ¹³C values clearly show, this technique enables the exclusion of a potential common source even when two samples have otherwise identical chemical and physical properties.

Analysis of the hydrogen and oxygen stable isotope ratios of beverage waters without prior water extraction using isotope ratio infrared spectroscopy

Hydrogen (δ(2)H) and oxygen (δ(18)O) stable isotope analysis is useful when tracing the origin of water in beverages, but traditional analytical techniques are limited to pure or extracted waters. We measured the isotopic composition of extracted beverage water using both isotope ratio infrared spectroscopy (IRIS; specifically, wavelength-scanned cavity ring-down spectroscopy) and isotope ratio mass spectrometry (IRMS). We also analyzed beer, sodas, juices, and milk 'as is' using IRIS. For IRIS analysis, four sequential injections of each sample were measured and data were corrected for sample-to-sample memory using injections (a) 1-4, (b) 2-4, and (c) 3-4. The variation between δ(2)H and δ(18)O values calculated using the three correction methods was larger for unextracted (i.e., complex) beverages than for waters. The memory correction was smallest when using injections 3-4. Beverage water δ(2)H and δ(18)O values generally fit the Global Meteoric Water Line, with the exception of water from fruit juices. The beverage water stable isotope ratios measured using IRIS agreed well with the IRMS data and fit 1:1 lines, with the exception of sodas and juices (δ(2)H values) and beers (δ(18)O values). The δ(2)H and δ(18)O values of waters extracted from beer, soda, juice, and milk were correlated with complex beverage δ(2)H and δ(18)O values (r = 0.998 and 0.997, respectively) and generally fit 1:1 lines. We conclude that it is possible to analyze complex beverages, without water extraction, using IRIS although caution is needed when analyzing beverages containing sugars, which can clog the syringe and increase memory, or alcohol, a known spectral interference.

Isotope fractionation during precipitation of methamphetamine HCl and discrimination of seized forensic samples

Methamphetamine is a widely abused illicit drug. Increasingly, studies have focused on stable isotope analysis by isotope ratio mass spectrometry (IRMS) to link samples of methamphetamine synthesized together or from the same source of precursor. For this reason, it is important to understand potential sources of isotope fractionation that could cause variability in forensic data sets. In this study, methamphetamine free base samples were synthesized from (−)-ephedrine HCl using the HI/red phosphorus synthetic route and then precipitated as HCl salts by bubbling with HCl gas. The entire sample did not precipitate when first bubbled with gas, and multiple precipitation steps were required. Fractions of precipitate were individually analyzed for δ 13C, δ 15N and δ 2H by IRMS. Both δ 15N and δ 2H were found to become more negative, with the heavy isotopes depleted, in successive fractions of precipitate. Homogenizing the precipitate fractions together could eliminate this fractionation. However, in a clandestine situation this fractionation could lead to greater than expected δ 15N and δ 2H variability between illicit samples of methamphetamine HCl that have been synthesized from the same sample of ephedrine. This needs to be taken into account when interpreting forensic IRMS data. We also present an analysis of four separate seized case lots of methamphetamine HCl, taking into account the possible sources of fractionation and available intelligence information.

Relative Tropospheric Photolysis Rates of HCHO and HCDO Measured at the European Photoreactor Facility

The relative photolysis rates of HCHO and HCDO have been studied in May 2004 at the European Photoreactor Facility (EUPHORE) in Valencia, Spain. The photolytic loss of HCDO was measured relative to HCHO by long path FT-IR and DOAS detection during the course of the experiment. The isotopic composition of the reaction product H(2) was determined by isotope ratio mass spectrometry (IRMS) on air samples taken during the photolysis experiments. The relative photolysis rate obtained by FTIR is j(HCHO)/j(HCDO) = 1.58 +/- 0.03. The ratios of the photolysis rates for the molecular and the radical channels obtained from the IRMS data, in combination with the quantum yield of the molecular channel in the photolysis of HCHO, Phi(HCHO-->H(2)+CO) (JPL Publication 06-2), are j(HCHO-->H(2)+CO/jHCDO-->HD+CO) = 1.82 +/- 0.07 and j(HCHO-->H+HCO/(jHCDO-->H+DCO + jHCDO-->D+HCO)) = 1.10 +/- 0.06. The atmospheric implications of the large isotope effect in the relative rate of photolysis and quantum yield of the formaldehyde isotopologues are discussed in relation to the global hydrogen budget.

Identification of organically farmed Atlantic salmon by analysis of stable isotopes and fatty acids

Using isotope ratio mass spectrometry (IRMS), the ratios of carbon (δ 13C) and nitrogen (δ 15N) stable isotopes were investigated in raw fillets of differently grown Atlantic salmon (Salmo salar) in order to develop a method for the identification of organically farmed salmon. IRMS allowed to distinguish organically farmed salmon (OS) from wild salmon (WS), with δ 15N-values being higher in OS, but not from conventionally farmed salmon (CS). The gas chromatographic analysis of fatty acids differentiated WS from CS by stearic acid as well as WS from CS and OS by either linoleic acid or α-linolenic acid, but not OS from CS. The combined data were subjected to analysis using an artificial neural network (ANN). The ANN yielded several combinations of input data that allowed to assign all 100 samples from Ireland and Norway correctly to the three different classes. Although the complete assignment could already be achieved using fatty acid data only, it appeared to be more robust with a combination of fatty acid and IRMS data, i.e. with two independent analytical methods. This is also favourable with respect to a possible manipulation using suitable feed components. A good differentiation was established even without an ANN by the δ 15N-value and the content of linoleic acid. The general applicability in the context of consumer protection should be checked with further samples, particularly regarding the variability of feed composition and possible changes in smoked salmon.