Jani C. Ingram

Detection of 2-chloroethyl ethyl sulfide and sulfonium ion degradation products on environmental surfaces using static SIMS

2-Chloroethyl ethyl sulfide (CEES) is a simultant for the chemical warfare agent bis(2-chloroethyl)sulfide (also known as HD or mustard), and both molecules undergo hydrolysis and subsequent condensation in aqueous solution to form stable sulfonium ions. The sulfonium ions derived from CEES are directly detected on quartzic surfaces using static SIMS instrumentation, which employs a molecular ReO 4 - (250 D) primary ion and pulsed secondary ion extraction. Pulsed extraction mitigates surface charging, and the ReO 4 - primary particle is efficient at sputtering molecular surface species into the gas phase. CEES eliminates Cl - to form an ethyl thiiranium intermediate, which is susceptible to nucleophilic attack by water and methanol to form 2-hydroxyethyl ethyl sulfide and 2-methoxyethyl ethyl sulfide. These two products and unhydrolyzed CEES also function as nucleophiles that condense with the ethyl thiiranium intermediate, resulting in the formation of sulfonium ion aggregates that are observable using SIMS. The previously unreported methoxy-substituted sulfonium ion suggests that a variety of derivatives are possible if different nucleophiles are present in the vicinity of the ethyl thiiranium intermediate. This work demonstrates that the sulfonium ion aggregates are stable on mineral surfaces and also demonstrates the potential value of SIMS for the detection of unanticipated ionic species in monitoring applications where mustard and its degradation products are suspected.

Cs+ speciation on soil particles by TOF-SIMS imaging

Soil particles exposed to CsI solutions were analyzed by imaging time-of-flight secondary ion mass spectrometry and also by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS). The results showed that Cs(+) could be detected and imaged on the surface of the soil particles readily at concentrations down to 160 ppm, which corresponds to 0.04 monolayer. Imaging revealed that most of the soil surface consisted of aluminosilicate material. However, some of the surface was more quartzic in composition, primarily SiO(2) with little Al. It was observed that adsorbed Cs(+) was associated with the presence of Al on the surface of the soil particles. In contrast, in high SiO(2) areas of the soil particle where little Al was observed, little adsorbed Cs(+) was observed on the surface of the soil particle. Using EDS, Cs(+) was observed only in the most concentrated Cs(+)-soil system, and Cs(+) was clearly correlated with the presence of Al and I. These results are interpreted in terms of multiple layers of CsI forming over areas of the soil surface that contain substantial Al. These observations are consistent with the hypothesis that the insertion of Al into the SiO(2) lattice results in the formation of anionic sites, which are then capable of binding cations.

Secondary ion mass spectrometric characterization of nail polishes and paint surfaces.

A variety of paint and fingernail polish samples, which were visually similar, but had different chemical compositions and formulations, was analyzed using quadrupole static secondary ion mass spectrometry (SIMS). Coating distinction was easily achieved in many cases because of the presence of dominant ions derived from the components of the coating, which could be observed in the SIMS spectra. In other instances, coating distinction was difficult within a product line because of spectral complexity; for this reason and because of the large numbers of spectra generated in this study, multivariate statistical techniques were employed, which allowed the meaningful classification and comparison of spectra. Partial Least Squares (PLS) and Principal Component Analysis (PCA) were applied to quadrupole SIMS data. PCA showed distinct spectral differences between most spectral groups, and also emphasized the reproducibility of the SIMS spectra. When using PLS analysis, reasonably accurate coating identification was achieved with the data. Overall, the PLS model is more than 90% effective in identifying the spectrum of a particular coating, and nearly 100% effective at telling which coating components represented in the PLS models are not present in a spectrum. The level of spectral variation caused by sample bombardment in the SIMS analysis was investigated using Fourier transform infrared spectroscopy (FT-IR) and quadrupole static SIMS. Changes in the FT-IR spectra were observed and were most likely a result of a number of factors involving the static SIMS analysis. However, the bulk of the sample is unaltered and may be used for further testing.

Detection of 2-chloroethylethyl sulfide on soil particles using ion trap-secondary ion mass spectrometry.

2-Chloroethylethyl sulfide (CEES) is used as a simulant for mustard (HD) in a study to develop secondary ion mass spectrometry (SIMS) for rapid, semi-quantitative detection of mustard on soil. Selectivity and sensitivity are markedly improved employing multiple-stage mass spectrometry (MS(n)) using an ion trap SIMS. C(2)H(5)SC(2)H(4)(+) from CEES eliminates C(2)H(4) and H(2)S, which are highly diagnostic. CEES was detectable at 0.0012 monolayer on soil. This corresponds to approximately 15 ppm (mass/mass) for a soil having a surface area of 12 m(2) g(-1). A single analysis could be conducted using only 2 mg of soil in under 5 min.

Characterization of bis(alkylamine)mercury cations from mercury nitrate surfaces by using an ion trap secondary ion mass spectrometer

Mercury-cyclohexylamine (R-NH2, where R = c-C6H11) ions having the composition Hg(R-NH)2H+ can be formed by exposing the surface of Hg(NO3)n = 1,2 salts to gaseous primary amines and then sputtering the surface with a primary ion beam (ReO4−). The resultant ions can be stabilized and detected using an ion trap secondary ion mass spectrometer (IT-SIMS) instrument, which provides collisional stabilization that facilitates their observation. Isolation of the Hg(R-NH)2H+ ions followed by collisional activation produces daughter ions corresponding to (C6H10NH2)+ and Hg(R-NH)+. These assignments were supported by deuterium labeling experiments, which resulted in the formation of Hg(R-NH)(R-NH-d11)H+ and Hg(R-NH)2H+. The existence of the Hg(R-NH)2 compounds on the surface was verified using Raman spectroscopy, which showed a strong absorption at 590 cm−1 that corresponded to Hg-N stretching. Analogous ions could be formed with n-hexylamine, but no Hg-bearing ions were formed when starting with a secondary or a tertiary amine. This indicates that only primary amines will react with Hg-nitrate surfaces in this manner. Hg-amine ions could not be formed starting with other Hg salts: chloride, iodide, thiocyanate, sulfate, and oxide. These results suggest that surface derivatization using amines, coupled with an IT-SIMS instrument, may offer an approach for determining inorganic metal speciation on surfaces.

Static secondary ionization mass spectrometry analysis of tributyl phosphate on mineral surfaces: Effect of Fe(II)

The static secondary ionization mass spectrometry (SIMS) spectrum of tri-n-butyl phosphate (TBP) on a variety of basalt and quartz samples is affected by the chemical composition of the mineral surface. When TBP is adsorbed on Fe(II)-bearing surfaces, the compound undergoes concomitant H− abstraction and reduction, followed by the elimination of two C4H8 molecules to form an ion at m/z 137+. When TBP is adsorbed to quartz or other nonreducing surfaces, it merely undergoes protonation and elimination of three C4H8 molecules to form H4PO4+. When TBP is adsorbed to Fe(III)-bearing surfaces, it undergoes H− abstraction and elimination of two C4H8 molecules, to form an ion at m/z 153+. These conclusions are supported by model studies that employed FeO, Fe203, TBP, and tributyl phosphite. The results show that the SIMS spectrum is very sensitive to the mode of TBP adsorption on the mineral surface.

Identification of mineral phases on basalt surfaces by imaging SIMS

A method for the identification of mineral phases on basalt surfaces utilizing secondary ion mass spectrometry (SIMS) with imaging capability is described. The goal of this work is to establish the use of imaging SIMS for characterization of the surface of basalt. The basalt surfaces were examined by interrogating the intact basalt (heterogeneous mix of mineral phases) as well as mineral phases that have been separated from the basalt samples. Mineral separates from the basalt were used to establish reference spectra for the specific mineral phases. Electron microprobe and X-ray photoelectron spectroscopy were used as supplemental techniques for providing additional characterization of the basalt. Mineral phases that make up the composition of the basalt were identified from single-ion images which were statistically grouped. The statistical grouping is performed by utilizing a program that employs a generalized learning vector quantization technique. Identification of the mineral phases on the basalt surface is achieved by comparing the mass spectra from the statistically grouped regions of the basalt to the mass spectral results from the mineral separates. The results of this work illustrate the potential for using imaging SIMS to study adsorption chemistry at the top surface of heterogeneous mineral samples.

Preservation of yeast cell morphology for scanning electron microscopy using 3.28-μm IR laser irradiation

As an alternative to conventional fixation procedures for scanning electron microscopy (SEM) analysis, yeast cells (Saccharomyces cerevisiae) were irradiated in ambient air, with an intense 3.28-micro m IR laser pulse. The morphology of the irradiated cells was well preserved, while nonirradiated control cells were severely shriveled.

Rapid detection of tri-n-butyl phosphate on environmental surfaces using static SIMS

Abstract Static secondary ion mass spectrometry (SIMS) is an analytical method that can be used to detect the presence of tri-n-butyl phosphate (TBP) on environmental surfaces including minerals (e.g., basalts, quartz) and vegetation. Static SIMS instrumentation equipped with pulsed secondary ion extraction and a ReO4− primary ion gun permits the rapid acquisition of cation and anion mass spectra of samples surfaces with virtually no sample preparation: samples are merely attached to a sample holder using double-stick tape. SIM spectra were demonstrated to be sensitive to the mode of TBP adsorption to mineral surfaces: TBP adsorbed to Fe(II)-bearing phases, Fe(III)-bearing phases, silicate, and vegetation surfaces could be distinguished from one another. These results indicate that SIMS has broad applicability for the rapid characterization of environmental surfaces, and in some cases, is capable of identifying the mode of contaminant-surface interactions. The technique is also attractive because it can analyze milligram-size samples, and no waste is generated during analysis.

Calcite Precipitation and Trace Metal Partitioning in Groundwater and the Vadose Zone: Remediation of Strontium -90 and Other Divalent Metals and Radionuclides in Arid Western Environments

Radionuclide and metal contaminants are present in the vadose zone and groundwater throughout the U.S. Department of Energy (DOE) weapons complex. Demonstrating in situ immobilization of these contaminants in vadose zones or groundwater plumes is a cost-effective remediation strategy. However, the implementation of in situ remediation requires definition of the mechanism that controls sequestration of the contaminants. One such mechanism for metals and radionuclides is co-precipitation of these elements in authigenic calcite and calcite overgrowths. Calcite, a common mineral in many aquifers and vadose zones in the arid western U.S., can incorporate divalent metals such as strontium, cadmium, lead, and cobalt into its crystal structure by the formation of solid solutions. The rate at which trace metals are incorporated into calcite is a function of calcite precipitation kinetics, adsorption interactions between the calcite surface and the trace metal in solution, solid solution properties of the trace metal in calcite, and also the surfaces upon which the calcite is precipitating. A fundamental understanding of the coupling of calcite precipitation and trace metal partitioning and how this may occur in aquifers and vadose environments is lacking. The focus of the research proposed here is to investigate the facilitated partitioning of metal and radionuclides by their coprecipitation with calcium carbonate. Our specific research objectives include: (1) Elucidating the mechanisms and rates of microbially facilitated calcite precipitation and divalent cation adsorption/co-precipitation occurring in a natural aquifer as a result of the introduction of urea. (2) Assessing the effects of spatial variability in aquifer host rock and the associated hydro/biogeochemical processes on calcite precipitation rates and mineral phases within an aquifer.