Rapid Detection of Chemical Agent Residues on Environmental Surfaces Using an Ion Trap Sims

Technology for the rapid detection and identification of chemical agent (CA) residues on solid sample surfaces is being developed at the Idaho National Engineering and Environmental Laboratory (INEEL). The development effort is being undertaken because of the critical need for rapid and specific characterization of suspect environmental samples, preferably on-site. Secondary ion mass spectrometry (SIMS) is being pursued for these applications because SIMS combines rapid, specific, and sensitive surface analyses with the potential for small instrument size. This latter attribute suggests that field characterization using SIMS is possible; this avenue is being supported by the Department of Defense at the INEEL. This paper describes ongoing development and scientific efforts focused on the development of smallscale, transportable SIMS instrumentation and adsorbate detection on environmental surfaces. INTRODUCTION The Chemical Weapons Convention (CWC) prohibits the development, production, acquisition, stockpiling, transfer, and use of chemical weapons. Related chemical weapons agreements seek to ban chemical weapons and further monitor the production, consumption, processing, import, and export of chemical agents (CA) and scheduled chemicals. A critical aspect of investigating suspected cases of non-compliance is the detection and identification of CA, their precursors, and degradation products on environmental samples associated with the challenge inspection. This problem is substantial because of the high toxicity of the compounds and represents a significant safety hazard to inspection personnel working in the area. The prime requirement in analytical investigations for the use of CA is for the unequivocal detection and identification of the agent or scheduled compound. In order to achieve adequate verification, reliable and sensitive procedures are necessary. Most of these procedures are based on instrumental methods such as gas or liquid chromatography coupled with mass spectrometric techniques. These techniques are capable of ppb sensitivity, but solid samples, soils, paint surfaces, botanical materials, etc. must be extracted prior to analysis; this process is very labor intensive and can take several minutes to hours per sample. These lengthy extraction procedures severely limit the number of samples that can be analyzed on-site; therefore, sample screening is critical for selecting those samples that have the highest probability for positive detection. Additionally, screening for CA in complex environments is complicated because the most significant CA compounds readily undergo degradation reactions under environmental conditions, and the degradation products can strongly adsorb to soil surfaces. Consequently, thermal desorption and solvent extraction techniques for analysis are frequently ineffective or biased. These limitations suggest the need for development of alternative analytical procedures to facilitate investigations. Secondary ion mass spectrometry (SIMS) is a technique, which is particularly amenable to the detection of CA and their degradation products, because it interrogates soil and environmental surfaces where the adsorbate residues reside. SIMS operates by bombarding the surface of a small (3-4 mg) environmental sample with an energetic particle beam (Figure 1). This event causes sputtering of charged parent and fragment ions that are indicative of the identity of the CA adsorbed onto the sample surface. Initial demonstrations of this technique showed that approximately 0.1 monolayer of nerve agent and blister agent residues could be detected on soil surfaces. However, detection of smaller quantities was hindered by the presence of ubiquitous background chemicals that reside on every surface in the ambient environment; these chemicals served to obfuscate the adsorbate signature. The chemical background can be ejected from the SIMS analysis using an ion trap mass spectrometer (IT-SIMS), which can also be used for identification of the CA residues by specific fragmentation reactions. This approach has improved the detection limit by two orders of magnitude (0.001 monolayer) and improved the specificity of the analysis. Further, the development of the ITSIMS has also resulted in instrumentation that is smaller, more rugged, and more transportable. This paper describes the progress in instrument development and gives specific examples of applications.