Avik Mazumder

Application of high performance liquid chromatography coupled to on-line solid-phase extraction-nuclear magnetic resonance spectroscopy for the analysis of degradation products of V-class nerve agents and nitrogen mustard

The detection and identification of the degradation products of nitrogen mustard and nerve agent VX by high performance liquid chromatography coupled to on-line solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-UV-SPE-NMR) were demonstrated. The analytes selected for the study were N,N-dimethylaminoethanol (DMAE), N,N-diethylaminoethanol (DEAE), N,N-diisopropylaminoethanol (DIAE) and triethanolamine (TEA). Offline solid-phase extraction (SPE) followed by derivatization was applied to eliminate the interferents and make the analytes amenable for UV detection. Thereafter, chromatographically separated derivatives were trapped on on-line SPE cartridges. They were subsequently eluted and 1H NMR and COSY spectra were obtained. The overall detection limits of the LC-UV-SPE-NMR method for the mentioned analytes were found to be 18, 23, 25, and 32 mg/L respectively. Applicability of the method to real samples was demonstrated by the analysis of samples provided during the 22nd OPCW official proficiency test. The method gave reproducible NMR spectra devoid of intense background signals.

On-line high-performance liquid chromatography–ultraviolet–nuclear magnetic resonance method of the markers of nerve agents for verification of the Chemical Weapons Convention

This paper details an on-flow liquid chromatography-ultraviolet-nuclear magnetic resonance (LC-UV-NMR) method for the retrospective detection and identification of alkyl alkylphosphonic acids (AAPAs) and alkylphosphonic acids (APAs), the markers of the toxic nerve agents for verification of the Chemical Weapons Convention (CWC). Initially, the LC-UV-NMR parameters were optimized for benzyl derivatives of the APAs and AAPAs. The optimized parameters include stationary phase C(18), mobile phase methanol:water 78:22 (v/v), UV detection at 268nm and (1)H NMR acquisition conditions. The protocol described herein allowed the detection of analytes through acquisition of high quality NMR spectra from the aqueous solution of the APAs and AAPAs with high concentrations of interfering background chemicals which have been removed by preceding sample preparation. The reported standard deviation for the quantification is related to the UV detector which showed relative standard deviations (RSDs) for quantification within +/-1.1%, while lower limit of detection upto 16mug (in mug absolute) for the NMR detector. Finally the developed LC-UV-NMR method was applied to identify the APAs and AAPAs in real water samples, consequent to solid phase extraction and derivatization. The method is fast (total experiment time approximately 2h), sensitive, rugged and efficient.

A quantitative NMR protocol for the simultaneous analysis of atropine and obidoxime in parenteral injection devices

A rapid selective and accurate quantitative (1)H NMR method was developed for the simultaneous analysis of obidoxime chloride and atropine sulfate, the active components in parenteral injection devices (PID) used for the emergency treatment of poisoning by toxic organophosphates. The spectra were acquired in 90% H(2)O-10% D(2)O using sodium 3-(trimethylsilyl)-1-propane sulfonate hydrate as the internal standard. Both synthetic mixtures and dosage forms were assayed. The results were compared with those obtained from a reported HPLC method.

High resolution 19F{1H} nuclear magnetic resonance spectroscopy and liquid chromatography–solid phase extraction–offline 1H nuclear magnetic resonance spectroscopy for conclusive detection and identification of cyanide in water samples

We report herein a new, sensitive and efficient method for detection, identification and quantification of cyanide in water samples. Cyanide was converted (>95% yield) to its versatile and stable derivative, 1-cyano-2,2,2-trifluoro-1-phenylethyl acetate (CTPA).The crude reaction mixture was directly subjected to high resolution fluorine-19 nuclear magnetic resonance ((19)F{(1)H} NMR) spectroscopy. In order to do away with signal overlap and dynamic range problems associated with (1)H NMR spectroscopy, liquid chromatography with UV detection hyphenated to online solid phase extraction (LC-UV-SPE) was performed. The trapped and enriched CTPA was thereafter subjected to offline (1)H NMR spectroscopy. In this way the δ(1)H, δ(19)F spectral signatures and LC-UV retention time were used for specific detection and identification and quantification of cyanide. The three techniques (viz. LC-UV and LC-UV-SPE followed by offline (1)H NMR and (19)F{(1)H} NMR spectroscopy) demonstrated good linearity (r(2)>0.99), reproducibility (inter-day RSD: 1.43-1.89%, 2.60-2.80%, 1.42-1.60; intra-day: RSD 1.20-1.38%, 3.21-3.25%, 1.00-1.19%), accuracy (recoveries: 95.1-97.2%, 77.5-82.8%, 96.8-98.9%) and LODs (1.31 μg/mL, 4.24 μg/mL, and 2.14 μg/mL) respectively. Total time required for the analysis was ∼3 h. Utility of the method was demonstrated by the detection and identification of spiked water samples. Since the derivative CTPA was volatile, could also be analyzed by GC-MS and GC-FTIR instruments.

Gas chromatography-mass spectrometric analysis of trimethylsilyl derivatives of toxic hydrolyzed products of nerve agent VX and its analogues for verification of Chemical Weapons Convention

The formation of trimethylsilyl (TMS) derivative of hydrolyzed product of nerve agent VX, namely S-2-(N,N-diisopropylaminoethyl) methylphosphonothiolate (EA-2192), was reported to be hampered due to its zwiterionic character. Contrary to this assumption, we have synthesized and analyzed the TMS derivative of EA-2192 and its analogues. Initially, the problem of non-detectability in GC-MS analysis was found to be due to their condensation followed by decomposition on GC column. An optimized temperature program, starting from 175 °C column temperature, favours partitioning of TMS derivatives of EA-2192 and its analogues into mobile phase, which facilitates their detection. It reduces their on-column condensation and decomposition. Excellent reproducibility (<1% RSD) of TMS derivatives of S-2-(N,N-dialkylaminoethyl) alkylphosphonothiolates was achieved by GC-MS analysis with temperature program of 175 °C (2 min)–10 °C min−1– 300 °C (5 min). Under the optimized conditions LODs ranged from 8–10 μg mL−1 for different analytes at a split ratio of 1 : 10.

Gas chromatography electron ionization mass spectrometric analysis of O -alkyl methylphosphinates for verification of Chemical Weapons Convention

We describe the gas chromatography/mass spectrometric (GC/MS) analysis of O-alkyl methylphosphinates (AMPs), which are included in Schedule 2B4 chemicals in the Chemical Weapons Convention (CWC). GC/MS analysis of a variety of AMPs and their deuterated analogs revealed that their fragmentations were determined by α-cleavages, McLafferty +1 and hydrogen rearrangement. Based on the obtained electron ionization mass spectra of AMPs, the fragmentation routes were rationalized, which were substantiated by the GC/MS analysis of deuterated analogs.

Polymer supported N-benzyl-N-nitroso-4-toluenesulfonamide: An improved reagent for the derivatization of the acidic markers of nerve agents

We report herein the synthesis, characterization, stability study of a new solid supported derivatizing agent, N-benzyl-N-nitroso-4-poly(styrene-co-divinylbenzene)sulfonamide beads, for the preparation of phenyldiazomethane (PDM). The active component loading was found to be 2.0 ± 0.1 mmol g−1. This derivatizing agent is easy to synthesize and purify. The impurities and byproducts generated during the formation of PDM remain bound to the polymer backbone. These byproducts can be easily removed by filtration. Thus, pure PDM is obtained without the need for further purification. Due to the formation of a dilute solution of PDM, the chances of explosion and intoxication are minimized. The PDM from this derivatizing agent was used for the benzylation of a variety of acids. We have evaluated this derivatizing agent for the benzylation of alkylphosphonic acids (APAs) and alkyl alkylphosphonic acids (AAPAs). Subsequently, this reagent was applied for analysis of a real sample containing pinacolyl methylphosphonic acid by onflow LC-UV-1H NMR analysis.

Oxidative decontamination of chemical warfare agent VX and its simulant using N,N-dichlorovaleramide

The optimized conditions have been reported for efficient, operationally simple and safe oxidative decontamination of chemical warfare agent O-ethyl-S-2-(N,N-diisopropylaminoethyl)methylphosphonothioate (VX) and its non-toxic simulant O,S-diethyl methylphosphonothioate (OSDEMP). A positive chlorine bearing reagent N,N-dichlorovaleramide (NCV) was tested successfully to effect decontamination of these compounds. These compounds were found to undergo instantaneous reaction with NCV in acetonitrile–water medium to form non-toxic products. The reaction was monitored by gas chromatography (GC) and the products were identified by gas chromatography coupled with mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy. The advantages of using this reagent are its low cost of production, ease of synthesis from commercially available raw materials and good shelf life (of more than one year).

Microwave Induced Synthesis of O,O-Dialkyl Dialkylpyrophosphonates under Solvent Free Conditions: Markers of Nerve Agents

This article describes a one pot, solvent free, microwave assisted synthesis of O,O-dialkyl dialkylpyrophosphonates (DADAPP) from O-alkyl alkylphosphonic chlorides 2a–j with 4-dimethylaminopyridine (DMAP) in the presence of water under microwave irradiation. The reaction takes place by the phosphonium salts, which are converted into the DADAPPs 4a–j. These DADAPPs are important markers of chemical warfare agents sarin, soman, and VX and their analogues. The method has several advantages over the conventional methods such as operational simplicity, high yield, and reduced reaction time.

A derivatization strategy for the detection and identification of volatile trialkylphosphites using liquid chromatography-online solid phase extraction and offline nuclear magnetic resonance spectroscopy

We demonstrate herein the application of selective derivatization method that converts volatile and labile trialkylphosphites (TAPs) into virtually non-volatile, thermally stable, and UV absorbing derivatives. After simple sample preparation, purification/enrichment of the derivatives was achieved by using high performance liquid chromatography (HPLC) coupled to on-line post column solid phase extraction (SPE) system. These derivatives were subjected to (31)P{(1)H} NMR and 1D-selTOCSY experiments. Conclusive identification was achieved on the basis of their HPLC retention time and NMR spectral signatures ( [Formula: see text] , (n)JH-H, and (3)JP-H). This method was tested for the unambiguous identification of a mixture containing low concentrations (∼10μgmL(-1)) of trimethylphosphite (TMP), triethylphosphite (TEP), triisopropylphosphite (TIP), and tributylphosphite (TBP) along with a high concentration of irrelevant background chemicals. It offered a high dynamic range and good detection limit and recovery (>75%) without the need for special NMR probe heads or exotic NMR experiments.