Paul A. D'Agostino

Determination of chemical warfare agents, their hydrolysis products and related compounds in soil

Abstract A procedure based on sequential hexane and dichloromethane extraction followed by trimethylsilyl derivatization and capillary column gas chromatographic-mass spectrometric (GC-MS) confirmation was developed for the verification of chemical warfare agents, their hydrolysis products and related compounds in soil. The chemical warfare agents sarin, soman and mustard and the simulant triethyl phosphate were added to four different soil types at the 50 and 5 μg/g levels and recovered with efficiencies varying from nearly 100% to about 5%. The recovery efficiencies were in the range 50–90% for most soil types contaminated with soman, mustard and triethyl phosphate. Sarin recovery was generally the lowest (5–30%). Hydrolysis products, due to degradation of the spiked chemical warfare agents during the course of the experiments, were detected and confirmed as trimethylsilyl derivatives. The developed sample handling and analysis procedure was applied to soil samples in support of range clearance operations. The chemical warfare agent tabun and sixteen related components and their hydrolysis products were identified during capillary column GC-MS analysis of soil extracts.

Desorption electrospray ionization mass spectrometric analysis of organophosphorus chemical warfare agents using ion mobility and tandem mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) has been applied to the direct analysis of sample media for target chemicals, including chemical warfare agents (CWA), without the need for additional sample handling. During the present study, solid-phase microextraction (SPME) fibers were used to sample the headspace above five organophosphorus CWA, O-isopropyl methylphosphonofluoridate (sarin, GB), O-pinacolyl methylphosphonofluoridate (soman, GD), O-ethyl N,N-dimethyl phosphoramidocyanidate (tabun, GA), O-cyclohexyl methylphosphonofluoridate (cyclohexyl sarin, GF) and O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate (VX) spiked into glass headspace sampling vials. Following sampling, the SPME fibers were introduced directly into a modified ESI source, enabling rapid and safe DESI of the toxic compounds. A SYNAPT HDMS instrument was used to acquire time-aligned parallel (TAP) fragmentation data, which provided both ion mobility and MS(n) (n = 2 or 3) data useful for the confirmation of CWA. Unique ion mobility profiles were acquired for each compound and characteristic product ions of the ion mobility separated ions were produced in the Triwave transfer collision region. Up to six full scanning MS(n) spectra, containing the [M + H](+) ion and up to seven diagnostic product ions, were acquired for each CWA during SPME fiber analysis. A rapid screening approach, based on the developed methodology, was applied to several typical forensic media, including Dacron sampling swabs spiked with 5 microg of CWA. Background interference was minimal and the spiked CWA were readily identified within one minute on the basis of the acquired ion mobility and mass spectrometric data.

Mass spectrometric analysis of chemical warfare agents and their degradation products in soil and synthetic samples.

A packed capillary liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed for the identification of chemical warfare agents, their degradation products and related compounds in synthetic tabun samples and in soil samples collected from a former mustard storage site. A number of organophosphorus and organosulfur compounds that had not been previously characterized were identified, based on acquired high-resolution ESI-MS data. At lower sampling cone voltages, the ESI mass spectra were dominated by protonated, sodiated and protonated acetonitrile adducts and/or their dimers that could be used to confirm the molecular mass of each compound. Structural information was obtained by inducing product ion formation in the ESI interface at higher sampling cone voltages. Representative ESI-MS mass spectra for previously uncharacterized compounds were incorporated into a database as part of an on-going effort in chemical warfare agent detection and identification. The same samples were also analyzed by capillary column gas chromatography (GC)-MS in order to compare an established method with LC-ESI-MS for chemical warfare agent identification. Analysis times and full-scanning sensitivities were similar for both methods, with differences being associated with sample matrix, ease of ionization and compound volatility. GC-MS would be preferred for organic extracts and must be used for the determination of mustard and relatively non-polar organosulfur degradation products, including 1,4-thioxane and 1,4-dithiane, as these compounds do not ionize during ESI-MS. Diols, formed following hydrolysis of mustard and longer-chain sulfur vesicants, may be analyzed using both methods with LC-ESI-MS providing improved chromatographic peak shape. Aqueous samples and extracts would, typically, be analyzed by LC-ESI-MS, since these analyses may be conducted directly without the need for additional sample handling and/or derivatization associated with GC-MS determinations. Organophosphorus compounds, including chemical warfare agents, related compounds and lower volatility hydrolysis products may all be determined during a single LC-ESI-MS analysis. Derivatization of chemical warfare agent hydrolysis products and other compounds with hydroxyl substitution would be required prior to GC-MS analysis, giving LC-ESI-MS a definite advantage over GC-MS for the analysis of samples containing chemical warfare agents and/or their hydrolysis products.

Analysis of bioactive peptides by liquid chromatography-high-resolution electrospray mass spectrometry.

LC-high-resolution electrospray ionization (ESI)-MS data for a number of bioactive peptides, including substance P and bradykinins were acquired over a wide mass range by scanning the magnetic sector and calibrating externally with polyethylene glycol standards. Multiply charged ions were observed and errors between observed and theoretical monoisotopic molecular masses were typically in the 5 to 30 ppm range for the peptides during LC-ESI-MS and ESI-MS operation with magnetic sector resolutions between 2500 and 6000 (10% valley definition). Under collisionally activated dissociation conditions bn- and yn-series sequence ions were generally observed, enabling amino acid sequencing and the differentiation of lysine from glutamine, two amino acids differing in residue mass by only 0.0364 u. Mass accuracy was evaluated during an international round robin analytical exercise where the molecular masses of five unknown peptides were to be accurately determined. Isotopic clusters for charge states of up to +6 were fully resolved, facilitating the rapid and unambiguous assignment of charge states and calculation of monoisotopic molecular masses. Errors between theoretical and observed monoisotopic molecular masses were in the 2 to 18 ppm range for the five unknown peptides.

Liquid chromatographic–high-resolution mass spectrometric and tandem mass spectrometric identification of synthetic peptides using electrospray ionization

Liquid chromatography-high-resolution electrospray mass spectrometry (LC-ESI-MS) was investigated for the identification of known and unknown synthetic peptides in a research effort designed to evaluate the applicability of this and complementary MS techniques for peptide characterization and identification. The monoisotopic molecular masses of five related peptides with molecular masses between 2000 and 2500 u were acquired with a resolution of 3000 (10% valley). Under narrow and wide mass range magnetic sector scanning conditions monoisotopic molecular mass errors were typically in the 10-20 and 30-40 ppm range, respectively. Tryptic maps were generated for each peptide following LC-ESI-MS analysis and collisionally activated dissociation (CAD) in the ESI interface resulted in the production of characteristic product ions that enabled amino acid sequencing of the tryptic fragments. Unknown identification was demonstrated during analysis of an incomplete synthetic peptide reaction mixture. The synthesis of an 18 amino acid peptide, LTTAVKKVLTTGLPALIS, was not successful. In its place were six unknown peptides that were identified on the basis of monoisotopic molecular mass and amino acid sequence data. The monoisotopic molecular masses of these unknowns were determined to within 10-20 ppm with a resolution of 3500 (10% valley). Amino acid sequences for the six peptides were generated during ESI-MS-MS analysis. Finally two synthetic peptides differing only by the incorporation of a 13C at leucine were analysed with a resolution of 6000 (10% valley) to confirm that the isotopic distributions were consistent with theoretical expectations.

Analysis of irritants by capillary column gas chromatography-tandem mass spectrometry

Abstract Daughter spectra were obtained for the molecular and principal electron impact fragmentation ions of four irritants, 1-methoxycycloheptatriene, 2-chloroacetophenone, o -chlorobenzylidenemalononitrile and dibenz[ b , f ]-1,4-oxazepin, during capillary column GC-MS/MS analysis. The use of standardized collisional activated dissociation cell conditions resulted in the acquisition of daughter spectra suitable for identification and data-base generation purposes. Daughter operation detection limits of 100 pg ( S N > 10:1 ), for the highest molecular mass irritant, dibenz[ b , f ]-1,4-oxazepin, were obtained. This level of sensitivity was approximately the same as that routinely obtained for chemical warfare agents during capillary column GC-MS analysis under electro impact ionization conditions. The specificity of GC-MS/MS was demonstrated by spiking a complex diesel exhaust extract, with 1-methoxycycloheptatriene.

Capillary column gas chromatographic-tandem mass spectrometric analysis of phosphate esters in the presence of interfering hydrocarbons

Abstract Daughter, parent and constant neutral loss spectra, and multiple reaction ion monitoring data were all evaluated for the detection and confirmation of phosphate esters during capillary column GC-MS-MS analysis with a hybrid tandem mass spectrometer. Constant neutral loss and parent modes involve scanning of the sector, thus reducing the benefits of higher sector resolution, while daughter and multiple reaction ion monitoring data may be acquired with higher sector resolution. The benefit of higher sector resolution was demonstrated for the detection and confirmation of phosphate esters in the presence of diesel exhaust extract components at levels several orders of magnitude above that of the phosphate esters. Detection limits for daughter operation were approximately the same as those obtained during capillary column GC-MS analysis of standards under electron impact ionization, and S/N ratios in excess of 100:1 were observed during multiple reaction ion monitoring of the diesel exhaust extract spiked at the 200 pg level with phosphate esters.

Electrospray Mass Spectrometric Characterization of Six Therapeutic Oximes: HI-6, HS-6, Obidoxime, 2-PAM, TMB-4 and HLö-7

Pyridinium and bis-pyridinium oxime salts are currently in use or under development for treatment of patients exposed to organophosphorus nerve agents. The low volatility and thermal lability of these compounds limits the number of mass spectrometric approaches that may be used to characterize them. Electrospray mass spectrometry (ESI-MS), a relatively new ionization approach, was investigated as a possible technique for the characterization and identification of these oximes and their degradation products. Six therapeutic oxime salts, the bis-pyridinium oximes, HI-6, HS-6, obidoxime, TMB-4 and HLo-7, and the pyridinium oxime, 2-PAM, were analysed by ESI-MS, making use of collisionally-activated dissociation (CAD) in the ESI interface. The CAD mass spectrum of each oxime was acquired with two different sampling cone voltage settings and the quadrupole mass analyser associated with a hybrid tandem mass spectrometer was utilized for tandem mass spectrometry (MS/MS) and CAD-MS/MS applications including the reliable differentiation of similar bis-pyridinium oximes and the identification of a HI-6 decomposition product.