| 1. |
- Höjer Holmgren, Karin, et al.
(författare)
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Part 1 : Tracing Russian VX to its synthetic routes by multivariate statistics of chemical attribution signatures
- 2018
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Ingår i: Talanta. - : Elsevier. - 0039-9140 .- 1873-3573. ; 186, s. 586-596
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Tidskriftsartikel (refereegranskat)abstract
- Chemical attribution signatures (CAS) associated with different synthetic routes used for the production of Russian VX (VR) were identified. The goal of the study was to retrospectively determine the production method employed for an unknown VR sample. Six different production methods were evaluated, carefully chosen to include established synthetic routes used in the past for large scale production of the agent, routes involving general phosphorus-sulfur chemistry pathways leading to the agent, and routes whose main characteristic is their innate simplicity in execution. Two laboratories worked in parallel and synthesized a total of 37 batches of VR via the six synthetic routes following predefined synthesis protocols. The chemical composition of impurities and byproducts in each route was analyzed by GC/MS-EI and 49 potential CAS were recognized as important markers in distinguishing these routes using Principal Component Analysis (PCA). The 49 potential CAS included expected species based on knowledge of reaction conditions and pathways but also several novel compounds that were fully identified and characterized by a combined analysis that included MS-CI, MS-EI and HR-MS. The CAS profiles of the calibration set were then analyzed using partial least squares discriminant analysis (PLS-DA) and a cross validated model was constructed. The model allowed the correct classification of an external test set without any misclassifications, demonstrating the utility of this methodology for attributing VR samples to a particular production method. This work is part one of a three-part series in this Forensic VSI issue of a Sweden-United States collaborative effort towards the understanding of the CAS of VR in diverse batches and matrices. This part focuses on the CAS in synthesized batches of crude VR and in the following two parts of the series the influence of food matrices on the CAS profiles are investigated.
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| 2. |
- Höjer Holmgren, Karin
(författare)
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Route attribution of chemical warfare agents : Retrospective classification of unknown threat samples
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although chemical warfare agents (CWAs) are prohibited under international law, there have been numerous crimes that violates the 1997 Chemical Weapons Convention (CWC) during the last decade, especially in the civil war in Syria where sarin, mustard gas and chlorine have all been used. CWAs have also been used in political assassinations and attempts thereof. In such situations, it is important to identify the deployed CWA and to find information on how it was produced, as this information is potentially of considerable value for any ensuing judicial process. The development and use of advanced analytical methods and multivariate data analysis methods are required to produce this kind of robust forensic evidence and intelligence. This thesis describes conducted research that aims at retrospectively tracing the synthesis methods applied in the production of CWAs. In three studies, methods for the determination of the employed synthetic route have been assessed. The relative distribution of the impurities gave a unique profile – in effect a “chemical fingerprint” - that was used for retrospective determination of the production method of a specific CWA. The study in paper I was done on the nerve agent Russian VX, S-[2-(diethylamino)ethyl] O-isobutyl metylphosphonothioate, while paper II and III focused on sulfur mustard, bis(2-chloroethyl)sulfide. This thesis discusses the study set up, the choice of analytical methods, methods for data processing and the manner in which classification methods have been employed. The studies shows that the classification models could clearly separate the six production routes used in paper I and the five routes used in paper II. In paper III, a novel non-targeted approach in combination with high-resolution mass spectrometry allowed detection of additional low-concentration compounds in the sulfur mustard samples. This method produced data with sufficient information for classifying samples according to the production method of the precursor thiodiglycol (TDG). The performance of the classification models was successfully validated with test set samples. All test set samples were correctly assigned in paper I and paper II. The classification of TDG in paper III was more demanding, but still as much as 56-89% of the test set samples were correctly assigned. In addition to the established classification models, compounds with importance for route differentiation were identified, which gave enhanced information on the chemicals formed during the employed synthesis conditions. Their stability has also been investigated, and the results showed that the majority of the chemical attribution signatures (CASs) were stable at room temperature. The fourth study in this thesis (paper IV) is an international inter-laboratory comparison jointly conducted by eight defence research laboratories based in Europe, North America, Asia and Australia respectively. All participating laboratories analysed the same samples prepared at the Swedish Defence Research Agency (FOI). The impurity profiles in nerve agent precursor metylphosphonyl dichloride samples were compared by a gas chromatography mass spectrometry (GC/MS) method using a retention index to facilitate data comparison. Retention indices of 16 CASs were calculated and compared, and this showed that the between-laboratory variation was low. This work is a first step towards a harmonised laboratory method for the profiling of CWA samples. The methods developed in this thesis will enhance accurate source attribution of CWAs and could potentially be used when alleged use of a CWA is being investigated.
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| 3. |
- Höjer Holmgren, Karin, et al.
(författare)
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Route Determination of Sulfur Mustard Using Nontargeted Chemical Attribution Signature Screening
- 2021
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Ingår i: Analytical Chemistry. - : American Chemical Society. - 0003-2700 .- 1520-6882. ; 93:11, s. 4850-4858
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Tidskriftsartikel (refereegranskat)abstract
- Route determination of sulfur mustard was accomplished through comprehensive nontargeted screening of chemical attribution signatures. Sulfur mustard samples prepared via 11 different synthetic routes were analyzed using gas chromatography/high-resolution mass spectrometry. A large number of compounds were detected, and multivariate data analysis of the mass spectrometric results enabled the discovery of route-specific signature profiles. The performance of two supervised machine learning algorithms for retrospective synthetic route attribution, orthogonal partial least squares discriminant analysis (OPLS-DA) and random forest (RF), were compared using external test sets. Complete classification accuracy was achieved for test set samples (2/2 and 9/9) by using classification models to resolve the one-step routes starting from ethylene and the thiodiglycol chlorination methods used in the two-step routes. Retrospective determination of initial thiodiglycol synthesis methods in sulfur mustard samples, following chlorination, was more difficult. Nevertheless, the large number of markers detected using the nontargeted methodology enabled correct assignment of 5/9 test set samples using OPLS-DA and 8/9 using RF. RF was also used to construct an 11-class model with a total classification accuracy of 10/11. The developed methods were further evaluated by classifying sulfur mustard spiked into soil and textile matrix samples. Due to matrix effects and the low spiking level (0.05% w/w), route determination was more challenging in these cases. Nevertheless, acceptable classification performance was achieved during external test set validation: chlorination methods were correctly classified for 12/18 and 11/15 in spiked soil and textile samples, respectively.
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| 4. |
- Höjer Holmgren, Karin, et al.
(författare)
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Synthesis route attribution of sulfur mustard by multivariate data analysis of chemical signatures
- 2018
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Ingår i: Talanta. - : Elsevier BV. - 0039-9140 .- 1873-3573. ; 186, s. 615-621
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Tidskriftsartikel (refereegranskat)abstract
- A multivariate model was developed to attribute samples to a synthetic method used in the production of sulfur mustard (HD). Eleven synthetic methods were used to produce 66 samples for model construction. Three chemists working in both participating laboratories took part in the production, with the aim to introduce variability while reducing the influence of laboratory or chemist specific impurities in multivariate analysis. A gas chromatographic/mass spectrometric data set of peak areas for 103 compounds was subjected to orthogonal partial least squares - discriminant analysis to extract chemical attribution signature profiles and to construct multivariate models for classification of samples. For one- and two-step routes, model quality allowed the classification of an external test set (16/16 samples) according to synthesis conditions in the reaction yielding sulfur mustard. Classification of samples according to first-step methodology was considerably more difficult, given the high purity and uniform quality of the intermediate thiodiglycol produced in the study. Model performance in classification of aged samples was also investigated.
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| 5. |
- Nygren, Yvonne, 1965-, et al.
(författare)
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Hydrophilic interaction liquid chromatography (HILIC) coupled to inductively coupled plasma mass spectrometry (ICPMS) utilizing a mobile phase with a low-volatile organic modifier for the determination of cisplatin, and its monohydrolyzed metabolite
- 2008
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry. - 0267-9477 .- 1364-5544. ; 23:7, s. 948-954
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Tidskriftsartikel (refereegranskat)abstract
- This study demonstrates the on-line coupling of hydrophilic interaction liquid chromatography (HILIC) to inductively coupled plasma mass spectrometry (ICPMS). A low volatile organic solvent, dimethylformamide (DMF), was used as organic modifier of the mobile phase to minimize the solvent loading of the ICP and thereby improve analyte sensitivity and method robustness. The concept was illustrated by the selective determination of cisplatin (cis-DDP), and its mono-hydrolyzed metabolite (MH-DDP). Species were separated on a 2.1 × 150 mm ZIC-HILIC column and detected on-line by selective platinum (m/z 194 and 195) monitoring, giving a detection limit of 2 pg Pt (0.2 ng ml-1). Compared to the use of the conventional solvent acetonitrile (AcN), with DMF, cis-DDP sensitivity was enhanced as much as 36 times and no addition of oxygen to the plasma was needed to avoid carbon depositions on instrumental parts. Furthermore, several non-identified platinum containing compounds were observed when using AcN as a result of unwanted reactions between this solvent and the analytes. No such species were observed when DMF was used. The molecular structures of eluting compounds were verified by electrospray ionization mass spectrometry. Combined with a simple sample treatment protocol, the HILIC-ICPMS system allowed determination of free intracellular cis-DDP in in-vitro grown T289 human malignant melanoma cells up to 60 min after exposure to 50 g ml-1 cis-DDP for 1 h. This work shows that HILIC-ICPMS is a potent hyphenated technique for the analysis of hydrophilic metal compounds and that the use of chromatographic mobile phases with low-volatile organic solvents may be a generic approach to improve analyte sensitivity and system robustness of HPLC-ICPMS when mobile phases with high amount of organic solvent are used.
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| 6. |
- Subramaniam, Raja, et al.
(författare)
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An isomer-specific high-energy collision-induced dissociation MS/MS database for forensic applications : a proof-of-concept on chemical warfare agent markers
- 2011
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Ingår i: Journal of Mass Spectrometry. - : Wiley. - 1076-5174 .- 1096-9888. ; 46:9, s. 917-924
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Tidskriftsartikel (refereegranskat)abstract
- Spectra database search has become the most popular technique for the identification of unknown chemicals, minimizing the need for authentic reference chemicals. In the present study, an isomer-specific high-energy collision-induced dissociation (CID) MS/MS spectra database of 12 isomeric O-hexyl methylphosphonic acids (degradation markers of nerve agents) was created. Phosphonate anions were produced by the electrospray ionization of phosphonic acids or negative-ion chemical ionization of their fluorinated derivatives and were analysed in a hybrid magnetic-sector–time-of-flight tandem massspectrometer. A centre-of-mass energy (Ecom) of 65eV led to an optimal sequential carbon–carbon bond breakage, which was interpreted in terms of charge remote fragmentation. The proposed mechanism is discussed in comparison with the routinely used low-energy CID MS/MS. Even-mass (odd-electron) charge remote fragmentation ion series were diagnostic of the O-alkyl chain structure and can be used to interpret unknown spectra. Together with the odd-mass ion series, they formed highly reproducible, isomer-specific spectra that gave significantly higher database matches and probability factors (by 1.5 times) than did the EI MS spectra of the trimethylsilyl derivatives of the same isomers. In addition, ionization by negative-ion chemical ionization and electrospray ionization resulted in similar spectra, which further highlights the general potential of the high-energy CID MS/MS technique.
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| 7. |
- Subramaniam, Raja, et al.
(författare)
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Combination of solid phase extraction and in vial solid phase derivatization using a strong anion exchange disk for the determination of nerve agent markers
- 2009
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Ingår i: Journal of Chromatography A. - : Elsevier. - 0021-9673. ; 1216:48, s. 8452-9
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Tidskriftsartikel (refereegranskat)abstract
- Alkylphosphonic acids (APAs) are degradation products and chemical markers of organophosphorous (OP) nerve agents (chemical warfare agents). Anion exchange disk-based solid phase extraction (SPE) has been combined with in vial solid phase derivatization (SPD) and GC-MS analysis for the determination of APAs in aqueous samples. The optimization of critical method parameters, such as the SPD reaction, was achieved using statistical experimental design and multivariate data analysis. The optimized method achieved quantitative recoveries in the range from 83% to 101% (n=13, RSD from 4% to 10%). The method was sensitive, with LODs in SIM mode of 0.14ppb, and demonstrated excellent linearity with an average R(2)>/=0.99 over the concentration range of 0.07-1.4ppm in full scan mode and from 0.14ppb to 14ppb in SIM mode. For forensic applications, aqueous samples containing APAs at concentrations exceeding 14ppb were concentrated and target analytes were successfully identified by spectral library and retention index matching. Method robustness was evaluated using aqueous samples from the official OPCW Proficiency Test (round 19) and all APAs present in the sample were conclusively identified. The SPE disk retained the underivatized APAs in a stable condition for extended periods of time. No significant losses of APAs from the disk were observed over a 36-day period. Overall, the method is well suited to the qualitative and quantitative analysis of degradation markers of OP nerve agents in aqueous matrices with simplicity, a low risk of cross-contamination and trace level sensitivity.
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| 8. |
- Subramaniam, Raja, et al.
(författare)
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Determination of S-2-(N,N-diisopropylaminoethyl)- and S-2-(N,N-diethylaminoethyl) methylphosphonothiolate, nerve agent markers, in water samples using strong anion-exchange disk extraction, in vial trimethylsilylation, and gas chromatography-mass spectrometry analysis
- 2012
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier. - 0021-9673 .- 1873-3778. ; 1229, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- Since the establishment of the Chemical Weapons Convention in 1997, the development of analytical methods for unambiguous identification of large numbers of chemicals related to chemical warfare agents has attracted increased interest. The analytically challenging, zwitterionic S-2-(N,N-diisopropylaminoethyl) methylphosphonothiolate (EA-2192), a highly toxic degradation marker of the nerve agent VX, has been reported to resist trimethylsilylation or to result in an unacceptably high limit of detection in GC-MS analysis. In the present study, the problem is demonstrated to be associated with the presence of salt, which hinders trimethysilylation. EA-2192 was extracted from aqueous samples by use of a strong anion-exchange disk, derivatized as a trimethylsilyl derivative via in vial solid-phase trimethylsilylation and identified by GC-MS. The limits of detection were 10ng/mL and 100ng/mL (in a water sample) for SIM and SCAN mode respectively. The analytical method was found to be repeatable with relative standard deviation <10%. The performance of the method was evaluated using a proficiency test sample and environmental samples (spiked river water and Baltic Bay water) and compared with the commonly used evaporation-silylation method. The disk method displayed good tolerance to the presence of salt and the spiked EA-2192 was conclusively identified in all matrices. In addition, the applicability of the method was further demonstrated for other selected hydrolysis products of VX and Russian VX, namely S-2-(N,N-diethylaminoethyl) methylphosphonothiolate, ethyl methylphosphonic acid, methylphosphonic acid, and isobutyl methylphosphonic acid. For the synthesis of reference compounds, EA-2192 and its analog from degradation of the Russian VX isomer, the present methods were improved by using a polymer-bound base, resulting in >90% purity based on (1)H NMR. Based on the current results and earlier work on alkylphosphonic acids using the same method, we conclude that the method is a viable choice for the simultaneous determination of a wide range of degradation products of nerve agents - zwitterionic, monoacid, diacid, and monothioacid chemicals - with excellent performance.
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| 9. |
- Subramaniam, Raja, et al.
(författare)
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Direct derivatization and rapid GC-MS screening of nerve agent markers in aqueous samples
- 2010
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 82:17, s. 7452-7459
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Tidskriftsartikel (refereegranskat)abstract
- A rapid screening and identification method based on derivatization and gas chromatography mass spectrometry (GC-MS) has been developed for the detection of alkylphosphonic acids (APAs), the degradation products of organophosphorus nerve agents. The novel method described involves rapid (5 min) and direct derivatization of 25 muL aqueous sample using highly fluorinated phenyldiazomethane reagents (e.g., 1-(diazomethyl)-3,5-bis(trifluoromethyl)benzene). The APA derivatives are then screened by GC-MS negative ion chemical ionization (NICI) and identified by electron ionization (EI) mode. The conditions for the derivatization were optimized using statistical experimental design and multivariate data analysis. Method robustness was evaluated using aqueous samples from an official OPCW Proficiency Test and all APAs present in the sample were conclusively identified. Limits of detection for rapid screening using SIM NICI were between 5 and 10 ng/mL APA in aqueous sample, and for identification using full scan EI 100 ng/mL.
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