Assessment of Agent Monitoring Strategies for the Blue Grass and Pueblo Chemical Agent Destruction Pilot Plants (2012) / Chapter Skim
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4 Current Status of Surface Measurement Technologies and Potential ACWA Site Applications
4 Current Status of Surface Measurement Technologies and Potential ACWA Site Applications
Pages 59-94
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From page 59... ...
. Distinguishing the degree to which various analytical systems can provide these capabilities for chemical agents on or within specific matrices depends on the ability of the analytical system to characterize different phases of the target species (i.e., gas, liquid, and solid)
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Two recently developed surface measurement technologies based on mass spectrometry ambient ionization techniques have been commercialized and found widespread application: direct analysis in real time (DART)
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The heated gas exits the source heading toward the atmospheric pressure inlet of the mass spectrometer. The ions produced in the vapor phase between the DART insulator cap and the mass spectrometer inlet are formed by interaction of the electronic excited-state species of helium or neon or vibronically excited nitrogen with the sample.
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From page 62... ...
. PROPERTIES OF THE TARGET MOLECULES RELEVANT TO THEIR DETECTION BY AMBIENT MASS SPECTROMETRY Before examining details of recent advances in ambient mass spectrometry, it is useful to review the ionization schemes and mass spectrometer configurations that are generally used to detect chemical agents.
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From page 63... ...
In this case, reaction 4.1b occurs if the electron affinity of the chemical agent is greater than that of the reagent ion A Proton donors are the most commonly used ionization reagents in ambient ionization mass spectrometry.
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A common one in the atmospheric community involves F transfer from an appropriate fluoride donor reagent ion. In a prior NRC report on chemical agent monitoring, it was suggested that this class of reaction might be extended to detect chemical agents (NRC, 2005a)
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The ion energetics properties shown in Table 4-1 indicate that a number of positive chemical ionization reagents should readily ionize the target chemical agents. Electron transfer from an agent molecule to the reagent ion will occur for the common reagent NO+ for VX and H agents since their IPs are lower than that of NO (IP = 9.26 eV)
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Proton affinity 857 1,039 796 N/A (kJ/mol) Fluoride affinity 152 111 104 N/A (kJ/mol)
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. Published chemical ionization measurements of chemical agents confirm the ion reaction mechanisms discussed above.
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These technologies have been coupled to a variety of mass spectrometers equipped with atmospheric pressure interfaces with only minor modifications, enabling the identification of unknowns by fragmentation pattern matching to databases, elemental formula determination via accurate mass measurements, multianalyte quantitation, spatially resolved measurements, and selective ionization enhancement for target compounds of interest. Ambient MS sampling/ionization techniques such as DART and DESI have grown in popularity because they: Enable the sampling of analyte under atmospheric pressure conditions from both liquid and solid states remotely from the mass analyzer.
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From page 69... ...
STATUS OF SURFACE MEASUREMENT TECHNOLOGIES AND POTENTIAL APPLICATIONS 69 TABLE 4-2 List of Acronyms (Ordered Alphabetically) and Relevant References Describing Various Ambient Surface Sampling Techniques Acronym Name First Report Spray and solid-liquid extraction based DAPPI Desorption Atmospheric Pressure Photo Ionization Haapala et al., 2007 DESI Desorption Electrospray Ionization Takáts et al., 2004 DICE Desorption Ionization by Charge Exchange Chan et al., 2010 EASI Easy Ambient Sonicspray Ionization Haddad et al., 2006 LESA Liquid Extraction Surface Analysis Kertesz and Van Berkel, 2010 LMJ-SSP Liquid Micro Junction-Surface Sampling Probe Wachs and Henion, 2001 ND-EESI Neutral Desorption Extractive Electrospray Ionization Chen et al., 2007 PESI Probe Electrospray Ionization Hiraoka et al., 2007 Plasma-based DAPCI Desorption Atmospheric Pressure Chemical Ionization Takáts et al., 2005a DART Direct Analysis in Real Time Cody et al., 2005 DBDI Dielectric Barrier Discharge Ionization Na et al., 2007 DCBI Desorption Corona Beam Ionization Wang et al., 2010 FAPA Flowing Atmospheric Pressure Afterglow Andrade et al., 2008 LTP Low-Temperature Plasma probe Harper et al., 2008 Laser desorption/ablation based ELDI Electrospray-assisted Laser Desorption Ionization Shiea et al., 2005 IR-LAMICI Infrared Laser Ablation Metastable-induced Chemical Galhena et al., 2010 Ionization LADESI Laser-Assisted Desorption Electrospray Ionization Rezenom et al., 2008 LAESI Laser Ablation Electrospray Ionization Mass Spectrometry Nemes and Vertes, 2007 LDESI Laser Desorption Electrospray Ionization Sampson and Muddiman, 2009 MALDESI Matrix-Assisted Laser Desorption Electrospray Ionization Sampson et al., 2006 Acoustic-based LIAD-ESI Laser-Induced Acoustic Desorption-Electrospray Ionization Cheng et al., 2009 RADIO Radio-frequency Acoustic Desorption and Ionization Dixon et al., 2009 Other AP-TD/SI Atmospheric Pressure Thermal Desorption/Secondary Basile et al., 2010 Ionization BADCI Beta electron-assisted Direct Chemical Ionization Steeb et al., 2009 DEMI Desorption Electrospray/Metastable-Induced Ionization Nyadong et al., 2009 REIMS Rapid Evaporative Ionization Mass Spectrometry Schäfer et al., 2009 SwiFerr Switched Ferroelectric Plasma Ionizer Neidholdt and Beauchamp, 2011 SOURCE: Adapted from Harris et al., 2011.
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From page 70... ...
Plasma-based ambient MS instrumentation tends to be fairly simple and rugged and can be coupled to a variety of mass spectrometers, including, most commonly, quadrupole ion traps, linear quadrupole ion traps, and quadrupole time-of-flight analyzers, providing MS/MS and/or accurate mass-determining capabilities for DART-produced ions. Plasma source mass spectra tend to be relatively simple, because most of the time the analytes are ionized, as described in the previous section, as one or two adduct types, simplifying peak assignment in the case of unknowns.
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FIGURE 4-3 Schematic illustrations showing the operation of several different ion sources and sampling schemes for ambient mass spectrometry. NOTE: HV = high voltage.
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Reactant is vaporized generating reactive species. ·Plasma-desorbed neutrals ionize by various mechanisms FIGURE 4-4 Additional illustrations showing the operation of several different ion sources and sampling schemes for ambient mass spectrometry.
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electrospray liquid. FIGURE 4-5 Laser-based ambient ionization techniques: (left)
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Analytes in droplets ·Sample is positioned to avoid direct interaction with ionize through ESI mechanisms. electrospray liquid.
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showing the operation of several different ion sources and sampling schemes for ambient mass spectrometry. SOURCE: Harris et al., 2011.
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Solvent molecular ions produced by reactions of neutral solvent molecules with metastables can also act as reagent ions, leading to both protonated analytes and analyte molecular ions. In the case of negative ion mode experiments, electron capture, dissociative electron capture, proton transfer, and anion attachment were hypothesized to be prevalent reaction pathways (Song et al., 2009a)
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Structures of the neutral molecules along with the exact masses of the detected quasimolecular ions are displayed in Figure 4-8. The production of oxidizing species is a mitigating issue in many of the plasma-based ambient ionization methods.
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A follow-up article by the same team demonstrated the possibility of performing rapid separations within the DART ionization region by ramping the DART gas temperature, which made it possible to distinguish the [M + NH4] + ion of GB from isobaric analytes that could otherwise only be resolved via high-resolution mass measurements or tandem mass spectrometric experiments (Nilles et al., 2010)
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Copyright 2009 American Chemical Society. FIGURE 4-9 High-resolution mass spectra obtained by DART for 800 ng VX on aluminum, concrete, and a bird feather.
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in the m/z region appropriate for the agents investigated. Desorption Electrospray Ionization (DESI)
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The desorption and ionization steps occurring simultaneously in DESI can be spatially and temporally separated for further control and optimization of the experimental parameters. This is the case in a technique known as laser ablation/desorption electrospray ionization (LADESI)
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. Nonproximate Analysis by Ambient Mass Spectrometry The need for field-portable nonproximate detection is apparent for compounds harmful to health or the environment, such as toxic industrial species, explosives, CWA and environmental toxins (Badman and Cooks, 2000; Gao et al., 2006; Mulligan et al., 2006; Chaudhary et al., 2006)
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From page 83... ...
For example, the Bruker Scanning Infrared Gas Imaging System 2 is a sensing system for remote infrared detection of hazardous gases in industrial, environmental, and homeland security applications.2 In traditional MS analysis of field samples with ambient mass spectrometry techniques, the ionization source is located close to the atmospheric pressure inlet of the mass spectrometer, limiting the analysis to small, well-defined sample substrates (Dixon et al., 2007)
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The DESI source is remotely located from the mass spectrometer, with ions transported over distances up to 3 m through a flexible stainless steel tube. SOURCE: Cotte-Rodriguez and Cooks, 2006.
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interfaced to a linear quadrople ion trap-MS with an ESI or DESI ion source; the inset photograph shows the actual injector. SOURCE: Dixon et al., 2007.
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. These large-area nonproximate analysis modes, which have been particularly well implemented with DESI, could find uses in mapping chemical agent contamination on equipment or building surfaces.
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Army Program Manager for Chemical Demilitarization, in which an atmospheric pressure ionization tandem quadrupole mass spectrometer system was used to directly detect GB and VX in air with a 15-sec response time and with detection limits of 7.2 ppt for GB and 6 ppt for VX (Ketkar et al., 1991b)
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Finally, because most of the published applications of both DESI and DART, including the chemical warfare agent and agent simulant studies described above, are laboratory-scale experiments performed under carefully controlled conditions, in which very small amounts of the target species are present on sample substrates of modest extent, the mobilization and dispersion of target species were seldom either a scientific or a safety issue and were not generally considered or commented on in those studies. However, the potential ACWA applications defined in this report may involve much higher levels of chemical agent contamination where target species dispersion is potentially much more serious.
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directly with action protocols Ability to track agent concentration gradients False positive rates reasonably well in the vapor phase (only DART) characterized through long record of Ability to remotely sample through wands utilization Simultaneous measurement of multiple Agent calibration reference standards agents during changeover and are readily available and utilized with decommissioning with high selectivity regular frequency through analytical and confirmatory signals Established regulatory guidelines are Potential for rapid changeover of multiple available for vapor and vapor headspace types of ion sources for enhanced selectivity analyses and spatial resolution Potentially easier instrumental clean-up Potential for validation through monitoring from contamination by analyzing both agent ions and product degradation concentrated samples fragmentation ions Analysis in near real time (msec or sec)
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When compared to existing vapor monitoring (DAAMS and MINICAMS) measurement strategies, ambient ionization mass spectrometry provides the following capabilities for detection and quantitation of chemical agents and their degradation products (see also Table 4-3)
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The platform configuration most likely to satisfy the analytical needs put forward in the various scenarios in Chapter 3 for different waste streams consists of a cart-mounted or handheld mass spectrometer equipped with a modified interface to accommodate a special remote sampling wand, a surface ambient ionization source combined with a vapor ambient ionization source, and any sampling accessories. Ambient ionization mass spectrometry systems backed by an uninterrupted power supply will allow portability between different rooms or site areas without breaking vacuum.
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From page 92... ...
Suggested mass analyzers are either triple quadrupole or linear ion trap, because both can be operated in selective reaction monitoring modes for validation of agent identification and reduction of false positives without requiring high mass resolution. The instrument's atmospheric pressure interface should be fitted with an optionally heated transfer line designed to serve as a multifunction sampling wand.
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From page 93... ...
Recommendation 4-4. Procedures developed and optimized in laboratory environments for the real-time detection of chemical agents using ambient ionization mass spectrometry should be verified in all working environments where they are likely to be deployed, using actual sample materials (e.g., activated charcoal from filter beds and worker masks, DPE suit material, and polymer-coated concrete)
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From page 94... ...
94 ASSESSMENT OF AGENT MONITORING STRATEGIES FOR BGCAPP AND PCAPP both to quantify measurements and to verify acceptable performance during critical operations. Even though they may be less reliable for quantitative analysis, calibration standards and procedures should also be developed that ensure acceptable sensitivity for detection of trace amounts of agents on relevant surfaces.
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