The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Gary Mallard - One of the best experts on this subject based on the ideXlab platform.

  • thermally assisted methylation and subsequent silylation of scheduled acids of Chemical Weapon convention for on site analysis and its comparison with the other methods of methylation
    Journal of Chromatography A, 2011
    Co-Authors: Kanchanavadee Amphaisri, Meehir Palit, Gary Mallard
    Abstract:

    On-site verification of the Chemical Weapon convention (CWC) requires provision for the detection and identification of alkyl phosphonic acids as well as some organic acids that are amenable to GC-MS only after derivatisation. Various derivatisation methods have been used for the identification of these acids and for many cases the methyl derivatives are less prone to artifacts possibly leading to false positive identification. Methylation with diazomethane is widely used but, especially for on-site analysis it has limitation due to the potential explosive and health hazards. Other methylation procedures like trimethylsilyldiazomethane (TMSD), thermally assisted methylation (TAM) by trimethylphenylammonium hydroxide (TMPAH) and trimethylsulfonium hydroxide (TMSH) are evaluated. Data for methylation for the alkyl alkylphosphonic acids, alkylphosphonic acids and benzilic acid are reported. In addition, TAM followed by the silylation in the same sample without any additional sample preparation is also reported. Several parameters such as solvent, temperature, amount of reagents, time, etc. were studied. The two commercially available reagents namely, TMPAH and TMSH for TAM and subsequent silylation were evaluated. The LOD with TMPAH was below 0.5 ng per injection since all of the acids were detected by GC-MS with the S/N of >3 in full scan mode by AMDIS and their inter day relative standard deviation was from 4.7% to 10.8%.

  • fragmentation energy index for universalization of fragmentation energy in ion trap mass spectrometers for the analysis of Chemical Weapon convention related Chemicals by atmospheric pressure ionization tandem mass spectrometry analysis
    Analytical Chemistry, 2009
    Co-Authors: Meehir Palit, Gary Mallard
    Abstract:

    The use of mass spectra generated at 70 eV in electron ionization (EI) as a universal standard for EI has helped in the generation of searchable library databases and had a profound influence on the analytical applications of gas chromatography/mass spectrometry (GC/MS), similarly for liquid chromatography tandem mass spectrometry (LC−MS/MS), suggesting a novel method to normalize the collisional energy for the universalization of fragmentation energy for the analysis of Chemical Weapon Convention (CWC)-related Chemicals by atmospheric pressure ionization-tandem mass spectrometry (API-MSn) using three-dimensional (3D) ion trap instruments. For normalizing fragmentation energy a “fragmentation energy index” (FEI) is proposed which is an arbitrary scale based on the fact of specific MS/MS fragmentation obtained at different collisional energies for the reference Chemicals which are not CWC scheduled compounds. FEI 6 for the generation of an MSn library-searchable mass spectral database is recommended.

Junhua Xiao - One of the best experts on this subject based on the ideXlab platform.

  • forensic signatures of a Chemical Weapon precursor dmpadc for determination of a synthetic route
    Talanta, 2021
    Co-Authors: Zixuan Zhang, Haibo Liu, Hui Tang, Runli Gao, Chengxin Pei, Hongmei Wang, Junhua Xiao
    Abstract:

    Abstract Chemical forensics has been widely recognized as an important tool to investigate alleged use of Chemical Weapons and/or to identify the illicit production of Chemical warfare agents. This paper describes the use of gas chromatography and mass spectrometry (GC-MS) to determine Chemical attribution signatures (CAS) N,N-dimethylphosphoramidic dichloride (DMPADC), a key precursor of tabun, for tracking the production of tabun. Synthetic samples were identified and classified by using GC-MS and chemometrics. Analysis samples (n = 27) were collected from three synthetic DMPADC routes; 20 potential CAS were identified, and the structures of five CAS were assigned. Principal component analysis (PCA) was performed to summarize the distribution trend of the samples and to check for the presence of outliers. A Partial least squares discriminant analysis (PLSDA) model was established to discriminate and classify the synthetic samples. The proposed model in this paper has high predictive ability, and the test set samples can be correctly categorized.

D K Dubey - One of the best experts on this subject based on the ideXlab platform.

  • dispersive solid phase extraction for in sorbent fourier transform infrared detection and identification of nerve agent simulants in analysis for verification of Chemical Weapon convention
    Analytical and Bioanalytical Chemistry, 2011
    Co-Authors: Prabhat Garg, Avik Mazumder, Deepak Pardasani, Ajay Kumar Purohit, D K Dubey
    Abstract:

    The combination of dispersive solid-phase extraction (DSPE) and Fourier-transform infrared (FTIR) spectroscopy is presented for detection and quantification of markers and simulants of nerve agents. Hydrophilic–lipophilic balance (HLB) sorbent was used for extraction and enrichment of organophosphonates from water. When the extraction efficiency of DSPE was compared with that of conventional solid-phase extraction (SPE), DSPE was more efficient. Extraction conditions such as extraction time, and type and quantity of sorbent material were optimized. In DSPE, extracted analytes are detected and quantified on the sorbent using FTIR as analytical technique. Absorbance in FTIR due to P–O–C stretching was used for detection and quantification. Infrared absorbance of different analytes were compared by determining their molar absorptivities (e max). Quantitative analyses were performed employing modified Beer’s law, and relative standard deviations (RSDs) for intraday repeatability and interday reproducibility were found to be in the range 0.30–0.90% and 0.10–0.80% respectively. The limit of detection (LOD) was 5–10 μg mL−1. The applicability of the method was tested with an unknown sample prepared by mimicking the sample obtained in an international official proficiency test.

  • determination of acetonitrile hexane partition coefficient of o o dialkyl methylphosphonates by nmr spectroscopy for the verification analysis of Chemical Weapon convention
    Defence Science Journal, 2010
    Co-Authors: Avik Mazumder, Hemendra K Gupta, R K Srivastava, D K Dubey
    Abstract:

    The extractability of the O,O'-dialkyl methylphosphonates, (the important markers of nerve agents) included in the schedule 2B4 of the Chemical Weapons Convention (CWC) has been studied by NMR, the aim being the optimisation of extraction protocols routinely used for the identification of Convention-related Chemicals (CRCs) during Official Proficiency Tests (OPTs) conducted by the Organization for Prohibition of Chemical Weapons (OPCW) and for the off-site analysis of real field samples. The technique is easy to optimise, fast, nondestructive, and shows excellent reproducibility. Defence Science Journal, 2010, 60(5), pp.502-506 , DOI:http://dx.doi.org/10.14429/dsj.60.573

John L Provis - One of the best experts on this subject based on the ideXlab platform.

Neera Tewarisingh - One of the best experts on this subject based on the ideXlab platform.

  • phosgene oxime injury and associated mechanisms compared to vesicating agents sulfur mustard and lewisite
    Toxicology Letters, 2017
    Co-Authors: Dinesh G Goswami, Rajesh Agarwal, Neera Tewarisingh
    Abstract:

    Abstract Phosgene Oxime (CX, Cl2CNOH), a halogenated oxime, is a potent Chemical Weapon that causes immediate acute injury and systemic effects. CX, grouped together with vesicating agents, is an urticant or nettle agent with highly volatile, reactive, corrosive, and irritating vapor, and has considerably different Chemical properties and toxicity compared to other vesicants. CX is absorbed quickly through clothing with faster cutaneous penetration compared to other vesicating agents causing instantaneous and severe damage. For this reason, it could be produced as a Weaponized mixture with other Chemical warfare agents to enhance their deleterious effects. The immediate devastating effects of CX and easy synthesis makes it a dangerous Chemical with both military and terrorist potentials. Although CX is the most potent vesicating agent, it is one of the least studied Chemical warfare agents and the pathophysiology as well as long term effects are largely unknown. CX exposure results in immediate pain and inflammation, and it mainly affects skin, eye and respiratory system. There are no antidotes available against CX-induced injury and the treatment is only supportive. This review summarizes existing knowledge regarding exposure, toxicity and the probable underlying mechanisms of CX compared to other important vesicants’ exposure.

  • clinically relevant cutaneous lesions by nitrogen mustard useful biomarkers of vesicants skin injury in skh 1 hairless and c57bl 6 mice
    PLOS ONE, 2013
    Co-Authors: Neera Tewarisingh, Carl W White, Anil K. Jain, Swetha Inturi, Rajesh Agarwal
    Abstract:

    A paucity of clinically applicable biomarkers to screen therapies in laboratory is a limitation in the development of countermeasures against cutaneous injuries by Chemical Weapon, sulfur mustard (SM), and its analog nitrogen mustard (NM). Consequently, we assessed NM-caused progression of clinical cutaneous lesions; notably, skin injury with NM is comparable to SM. Exposure of SKH-1 hairless and C57BL/6 (haired) mice to NM (3.2 mg) for 12–120 h caused clinical sequelae of toxicity, including microblister formation, edema, erythema, altered pigmentation, wounding, xerosis and scaly dry skin. These toxic effects of NM were similar in both mouse strains, except that wounding and altered pigmentation at 12–24 h and appearance of dry skin at 24 and 72 h post-NM exposure were more pronounced in C57BL/6 compared to SKH-1 mice. Conversely, edema, erythema and microblister formation were more prominent in SKH-1 than C57BL/6 mice at 24–72 h after NM exposure. In addition, 40–60% mortality was observed following 120 h of NM exposure in the both mouse strains. Overall, these toxic effects of NM are comparable to those reported in humans and other animal species with SM, and thus represent clinically-relevant cutaneous injury endpoints in screening and optimization of therapies for skin injuries by vesicating agents.