Research Areas

Chemical Hazards

Dynamic Workplans and Adaptive Sampling and Analysis Programs
The ability to rapidly assess the presence/absence of environmental contaminants is an essential component of the nation's environmental restoration program. Each site, whether owned by the public or private sector, must be evaluated to determine whether risk to human health or the environment exists. If the data obtained supports the fact that an acceptable level or no risk exists at the site for the intended use, no further action is required. If, on the other hand, sufficient risk exists to require a full site characterization, the site investigation effort must delineate the nature, extent, direction, concentration, and rate of contaminant movement. Field analytics plays a key role in this process when data are produced quickly enough to make decisions in the field. This requires that neither sample collectors nor analysts sit idle waiting for one another. 

Dynamic workplans rely on an initial conceptual model and an adaptive sampling and analysis strategy.  Rather than dictate the details of the type of sample analysis to be performed and the location and number of samples to be collected, dynamic workplans specify the decision-making logic that will be used in the field to determine which analytes to analyze, where to collect the samples, and when to stop sampling. Adaptive sampling and analysis programs change as the conceptual model for the site is refined based on the results obtained in the field. The conceptual model is dynamic in nature; it changes as on-site activities proceed and reflects the "new" knowledge gained through field studies.  A successful adaptive sampling and analysis program requires analytical instrumentation and methods that are field-practical and can produce verifiable data fast enough to support the on-site decision making process.  Performance-based measurement systems meet this challenge
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Subsurface Detection of Organics
A real-time chemical sensor is being developed for detection of environmental pollutants as the sensor is advanced into the subsurface.  Soil-bound organics are thermally desorbed, collected, transferred to the surface, where aromatics and chlorinated compounds are detected by a photoionization or electron impact detector, respectively.  Upon detection, organics are transferred through a heated valve to a freeze-trap where they are concentrated prior to thermal desorption GC/MS analysis.  Research shows when moisture content is < 15%, recoveries are between 50 and 100% for most pollutants.  For groundwater, a membrane is used, which retards water from passing through the membrane but allows organics through.  Although extraction efficiency is lower, the sensor provides the best means to find dense nonaqueous liquids in groundwater.  Research is in progress to identify or make a high temperature membrane or solid material that can be heated to 400 ⁰C so that the same collection system can be used for soil and groundwater.

Real-time depth profiling of the subsurface provides continuous information as to the presence/absence of contaminants.  When coupled with dynamic workplan strategies and EPA’s TRIAD process, site and remedial investigations can be accomplished faster, cheaper, but most importantly, with data density sufficient to reduce decision uncertainties. New transfer lines and direct reading mass spectrometers are being interfaced to address homeland security and sick building applications.
Forensic Chemistry
Forensic studies rely on quantitative measurements of specific chemicals or families of chemically related compounds.  For coal tar, petroleum, combustion/explosion, and fire-related investigations, gas chromatography/mass spectrometry (GC/MS) data of benzothiophenes, polycyclic aromatic hydrocarbons (PAH), and their alkylated analogs (the C₁-C₄, saturated side chains) are used to distinguish contaminant source(s), assign blame, and proportion liability as well as determine degradation, evaporation, and washing rates due to interactions with the environment.

Quantitative identification by GC/MS is only possible when target compound mass spectra are unencumbered by coeluting compounds, which is not the case.  Chemical noise from the matrix masks target compound spectra making full scan (sample vs. library) spectral matching impossible to validate.  Selected ion monitoring (SIM), whether by molecular or multiple ions per homolog, has evolved into the technique of choice based on the false presumption that matrix interferences are minimized.

Research is aimed at developing methods based on spectral deconvolution to more accurately estimate homolog and degradation products of interest in environmental and crime scene investigations as well as drugs and drug breakdown products at trace levels in complex matrixes such as urine and tissue extracts.

Pesticides in Food
Rapid, accurate, and inexpensive analysis of pesticides in food and beverages is of primary importance, especially since governments continue to increase the number of compounds to be screened as well as measurement sensitivity.  The analysis of foods and beverages is complicated by the number (hundreds) of interfering compounds present in the sample.  Toward this end, we have made libraries of pesticides and analyzed them both as target compounds and unknowns.  We showed that the pesticides can be analyzed quantitatively independent of retention time information when the Ion Fingerprint^TM deconvolution algorithms are used.  When 112 pesticides at 4 ng per compound were injected on column as a standard or from orange oil-pesticide spiked solution and searched as unknowns, 110 of the 112 compounds were correctly identified, with the average pesticide recovery 101 ± 19%.  No false negatives were found, since ion signals were not acquired by the instrument for the two pesticides not detected in either the standard or fortified mixtures.  No false positives were detected despite the fact more than 750 widely different compounds were included in the library search.

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