Research Areas

Technology

Most food, beverage, fragrance, environmental, or petroleum-based samples contain hundreds of organic compounds.  Based on size and volatility, these chemicals are usually analyzed by gas chromatography (GC) and/or liquid chromatography (LC).  Unambiguous quantitative identification can only be provided when a mass spectrometer (MS) is used as the detector and only when fragmentation patterns produced by the MS are different.  For complex mixtures, where hundreds of compounds are present in the sample, coelution occurs making it extremely difficult, if not impossible, to distinguish one compound’s pattern from another.

Spectral Deconvolution
Mathematical algorithms have been developed to deconvolve mass spectral information when multiple compounds coelute.  Our process, called Ion Fingerprint Detection^TM, is patented and is capable of providing quantitative analysis.  It is based on three independent algorithms that extract target compound ions, compare their abundances to library values, and eliminate increased ion signal due to coeluting compounds that have common ions with the target compound.  In addition to deconvolution, we have integrated additional filters that compare the commonality of spectral information for and across each scan in the peak.  We have shown spectral deconvolution can be used to find isomers belonging to homologs of alkylated polycyclic aromatic hydrocarbons (PAH) for which no mass spectral information exists.  We call this process Combinatorial Library Building because we can take advantage of the fact that mechanistically, fragmentation can occur around aromatic rings in only so many ways.  Research is in progress to extend this approach to other benzene and PAH substituents.  A key feature of the deconvolution software is the ability to subtract the complete target compound mass spectrum from the TIC peak in which multiple compounds coelute, thereby, electronically removing interfering spectra and increasing the probability of identifying unknowns correctly.

Fast Gas Chromatography/Mass Spectrometry
Because we can separate spectra from coeluting compounds, we can now run the GC/MS at much faster rates. The technology needed to resistively heat GC columns is patented. Experiments show we can control the heating process from 5 ⁰C/s to 0.08 ⁰C/min and, when the applied voltage is 0, the column reaches ambient temperature in seconds.  The rapid measurement cycle time makes it economically feasible to analyze chemical threats in the field.

Subsurface Detection of Environmental Pollutants
We are developing a real-time chemical sensor to detect chemical threats (environmental pollutants) as the sensor is advanced into the subsurface.  A 400 ⁰C probe extracts vapor phase and soil-bound organics and transfers them to either a photoionization detector (PID) or GC/MS.  The PID provides immediate response and when triggered, a valve switches the gas flow from the PID to a freeze-trap, where sample is concentrated and then thermally desorbed for GC/MS analysis.  Because both detection systems are on-line, loss of analyte is nearly eliminated and both volatile and semivolatile organics (VOCs and SVOCs) are analyzed together.  In contrast to standard EPA methods, where VOCs and SVOCs are analyzed using two different GC/MS instruments, field instrumentation is reduced while sample throughput rates are unmatched.  Combining real-time sensing with fast GC/MS,and spectral deconvolution, hazardous waste sites can now be characterized quickly and economically.  Because site characterization data is rich in information, decision uncertainties are dramatically reduced, which is at the heart of EPA’s TRIAD process (systematic planning, dynamic workplans, and field analytics).

Product Profiling of Extremely Complex Mixtures
Automated sequential two-dimensional chromatography with MS detection is a separation method aimed at increasing separation space by applying chromatographic techniques whose mechanism of separation involves different mobile phases and orthogonal stationary phases.  For extremely complex mixtures in which VOCs and SVOCs make-up the sample different introduction techniques are also required, e.g., static and dynamic head space, twister and large volume injection.  Toward that end, we work with Gerstel to incorporate automated sample preparation and introduction techniques into the following sequential 2D systems: GC-GC, LC-LC, and LC-GC.  Based on these techniques, we can “heart-cut” and find specific compounds or families of compounds of interest.

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