Philip A. Smith

Detection of gas-phase chemical warfare agents using field-portable gas chromatography–mass spectrometry systems: instrument and sampling strategy considerations

Abstract Selection of sampling methods and GC–MS instrumentation for field analysis of dangerous chemicals should be based on desired performance. Using a combined, man-portable, GC–MS sampler, volatile compounds may be analyzed while in a contaminated atmosphere. Alternatively, a small solid-phase microextraction sampler allows analysis in a nearby clean area with stationary GC–MS instrumentation that offers advantages in sample throughput and the range of samples that may be analyzed.

Detection of VX contamination in soil through solid-phase microextraction sampling and gas chromatography/mass spectrometry of the VX degradation product bis(diisopropylaminoethyl)disulfide

A solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) sampling and analysis method was developed for bis(diisopropylaminoethyl)disulfide (a degradation product of the nerve agent VX) in soil. A 30-min sampling time with a polydimethylsiloxane-coated fiber and high temperature alkaline hydrolysis allowed detection with 1.0 microg of VX spiked per g of agricultural soil. The method was successfully used in the field with portable GC-MS instrumentation. This method is relatively rapid (less than 1 h), avoids the use of complex preparation steps, and enhances analyst safety through limited use of solvents and decontamination of the soil before sampling.

Application of headspace solid-phase microextraction and gas chromatography-mass spectrometry for detection of the chemical warfare agent bis(2-chloroethyl) sulfide in soil.

A field expedient analytical method for detecting the chemical warfare agent (CWA) sulfur mustard as a soil contaminant was developed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). Five commercially available SPME fibers were investigated to determine the optimal fiber, and extraction conditions. Polyacrylate and carbowax-divinylbenzene fiber coatings gave a statistically indistinguishable and best response compared to the other three types examined in a simple system studied without soil. The polyacrylate fiber coating was selected for study of a system in which sulfur mustard was spiked to an agricultural soil (Standard Reference Material 2709, San Joaquin type). With soil samples, the greatest sensitivity occurred by the addition of deionized water to spiked soil and extraction at ambient temperature for 20 min or longer. SPME sampling with GC-MS analyses afforded good reproducibility (relative standard deviation between 2 and 10%), and analyte concentrations as low as 237 ng/g were detected in soil (total ion chromatograms). As completed here, total time for sampling and analysis was just under 1 h, and use of organic solvents or special sample introduction equipment was avoided.

Solid-phase microextraction (SPME) for rapid field sampling and analysis by gas chromatography-mass spectrometry (GC-MS)

Modern gas chromatography-mass spectrometry (GC-MS) methods and equipment, with the sensitivity and structural information these methods provide, make GC-MS an excellent choice for field detection and identification of a range of organic chemicals. Numerous sampling techniques allow detection of GC-MS analytes in environmental matrices, although multiple sample-handling steps and use of extraction solvents increase the complexity and time needed to complete analyses. Solid-phase microextraction (SPME) has been shown to be suitable for sampling environmental contaminants from air, water and soil for GC-MS analysis. We provide applied examples of environmental samples collected and analyzed in the field using SPME-GC-MS for qualitative identification of workplace air contaminants from a poorly characterized paint and of gas-phase contaminants present during forensic and clean-up operations following a large fire involving aircraft fuel. In both instances, passive SPME sampling concentrated analytes from the air following short sampling periods and was followed immediately by GC-MS analysis in the field, without further sample preparation. The SPME sampling method is attractive for field use because of its portability, simplicity, broad applications, sensitivity, and favorable attributes as a sample-introduction method for GC-MS analyses.

Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX)

The chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H](+)) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H](+) ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine-d(15) provided evidence that [M+H](+) production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H](+) ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.

Identifying the effective concentration for spatial repellency of the dengue vector Aedes aegypti

BackgroundCurrent efforts are underway to quantify the chemical concentration in a treated air space that elicits a spatial repellent (deterrent) response in a vector population. Such information will facilitate identifying the optimum active ingredient (AI) dosage and intervention coverage important for the development of spatial repellent tools – one of several novel strategies being evaluated for vector-borne disease control. This study reports initial findings from air sampling experiments conducted under field conditions to describe the relationship between air concentrations of repellent AIs and deterrent behavior in the dengue vector, Aedes aegypti.MethodsAir samples were taken inside and outdoors of experimental huts located in Pu Tuey Village, Kanchanaburi Province, Thailand in conjunction with mosquito behavioral evaluations. A mark-release-recapture study design using interception traps was used to measure deterrency of Ae. aegypti against 0.00625% metofluthrin coils and DDT-treated fabric (2g/m2) within separate experimental trials. Sentinel mosquito cohorts were positioned adjacent to air sampling locations to monitor knock down responses to AI within the treated air space. Air samples were analyzed using two techniques: the U.S. Environmental Protection Agency (USEPA) Compendium Method TO-10A and thermal desorption (TD).ResultsBoth the USEPA TO-10A and TD air sampling methods were able to detect and quantify volatized AIs under field conditions. Air samples indicated concentrations of both repellent chemicals below thresholds required for toxic responses (mortality) in mosquitoes. These concentrations elicited up to a 58% and 70% reduction in Ae. aegypti entry (i.e., deterrency) into treated experimental huts using metofluthrin coils and DDT-treated fabric, respectively. Minimal knock down was observed in sentinel mosquito cohorts positioned adjacent to air sampling locations during both chemical evaluations.ConclusionsThis study is the first to describe two air sampling methodologies that are appropriate for detecting and quantifying repellent chemicals within a treated air space during mosquito behavior evaluations. Results demonstrate that the quantity of AI detected by the mosquito vector, Ae. aegypti, that elicits repellency is far lower than that needed for toxicity. These findings have important implications for evaluation and optimization of new vector control tools that function through mosquito behavior modification as opposed to mortality.

Solvating gas chromatography with chemiluminescence detection of nitroglycerine and other explosives

A separation technique known as solvating gas chromatography (SGC), which utilizes packed capillary columns and neat carbon dioxide as mobile phase, was used for the separation of nitroglycerine (NG) and other nitrogen-containing explosives including 2,6-dinitrotoluene (2,6-DNT), 2,4-dinitrotolulene (2,4-DNT), 2,4,6-trinitrotoluene (2,4,6-TNT), and pentaerythritol tetranitrate (PETN). SGC was coupled for the first time to a selective chemiluminescence thermal energy analyzer (TEA) detector for nitro-functional group specificity and sensitive detection of these compounds. TEA calibration curve for NG showed linearity in the sub-microg ml(-1) range. Soil samples containing NG were used to test the validity of the technique. Detector response of SGC-TEA versus SGC-flame ionization detection for NG was also evaluated.

Hand-Held Photoionization Instruments for Quantitative Detection of Sarin Vapor and for Rapid Qualitative Screening of Contaminated Objects

Suitable detectors are needed to support survey needs of incident responders and health care personnel who may receive patients from an incident with exposures to hazardous chemicals. In the health care setting, such a detector would avoid cross-contamination to workers, patients, and to the treatment facility and associated equipment. An ideal survey detector would be sensitive, hand-held, capable of extended battery operation, and would provide a nearly immediate detector response on exposure to a broad range of high-concern chemicals. For responders, important capabilities would include quantitative measurement of gas/vapor contamination, and for both response and health care settings, qualitative detection of contaminated people and objects. In this study, the operating characteristics of photoionization detector (PID) instruments were examined using O-isopropyl methylphosphonofluoridate (sarin) in a laboratory setting. Instrument response factors were calculated for quantitation of airborne sarin, and speed of detector response and recovery were examined with point-contaminated cloth material. By sampling a range of sarin-contaminated air, calculated isobutylene unit response factors for high-and moderate-sensitivity commercial PID instrument types were 11.3 and 14.0 (dry air) and 20.1 and 44.4 (50% relative humidity), respectively. Response of the PID systems was highly correlated to concentration sampled, with R2 values greater than or equal to 0.997 for all combinations of PID detector type and humidity. While not sensitive enough to warn the unprotected public against a chemical with an extremely low “safe” exposure concentration, quantitation with available PID instruments could be useful to quickly prioritize corrective measures for a PID-detectable chemical. Qualitative survey characteristics were examined for the more sensitive PID tested using a piece of cloth material contaminated by a 1.0 μ L droplet of liquid sarin. Rapid response and recovery times (seconds) were observed when the sampling inlet was moved close to and away from the point of contamination. Within the health care setting, hand-held PID instruments could fill an important and currently unmet need as a point source detector for liquid contamination from extremely dangerous chemicals to help identify contaminated surfaces and limit secondary contamination and exposures.

Directly Heated High Surface Area Solid Phase Microextraction Sampler for Rapid Field Forensic Analyses

A high-surface area solid phase microextraction (HSA-SPME) sampler is described for dynamic sampling at high air velocities (up to several hundred centimeters per second). The sampling device consists of a thin wire coated with carboxen/polydimethylsiloxane (carboxen/PDMS) material, wound in the annular space between two concentric glass tubes, providing a large trapping surface from which analytes may then be thermally desorbed with little power consumption upon resistive heating of the wire. Desorbed analytes are focused and reconcentrated on a microtrap that is subsequently resistively heated to introduce analytes for GC or GC/MS analysis. Benzene, toluene, ethylbenzene, and xylenes (BTEX) included in a 39-component toxic organics (TO-14) gas mixture were used to evaluate the efficiency of the HSA-SPME sampler. Quantitation of trace-level BTEX compounds present during weapons cleaning was completed using stepwise calibration. Detection limits of 0.2-6.9 pptr(v) were observed for these analytes using single ion monitoring GC/MS analysis, and an improvement in sensitivity of several orders of magnitude was achieved when compared to standard dynamic flow SPME with a commercially available 10 mm carboxen/PDMS fiber. The potential for rapid analyte uptake and improved sensitivity using the HSA-SPME design will make it possible to rapidly collect and analyze VOC samples in field settings using a portable hand-held pump and a small, low power GC/MS instrument. This system will be especially useful for situations involving forensics, public safety, and military defensive or intelligence needs where rapid, sensitive detection of airborne analytes is required.

Liberation of Hydrogen Cyanide and Hydrogen Chloride During High-Temperature Dispersion of CS Riot Control Agent

High temperature dispersion (greater than 700 degrees C) of the riot control agent orthochlorobenzylidenemalononitrile (CS) has previously been shown to produce a number of organic thermal degradation products through rearrangements and loss of cyano and chlorine substituents present on the parent CS compound. Until now the possibility that HCN and HCl might also be air contaminants produced during high temperature CS dispersion has not been examined. Air samples were collected to detect HCN and HCl as air contaminants released during high-temperature CS dispersion indoors. Sampling and analysis based on National Institute of Occupational Safety and Health methods 7904 and 6010 for HCN, and 7903 for HCl, showed evidence that both compounds were present in air samples collected. A reassessment of human health risks associated with exposure to CS riot control agent dispersed at high temperature should be conducted, and should consider the full range of contaminants produced during the dispersion process.