Analytical Chemistry - Environmental and Biomedical Measurements
Our group at the University of St. Thomas pursues research aimed at improving chemical measurements, and utilizes undergraduate students exclusively. Group members range in experience from incoming freshmen to seniors. I encourage students at all levels to contact me if they have any interest in joining the group. If you have interest in helping design and build instruments or in making biomedical and environmental measurements, please come and see me (OWS 461) or email me. Some general information on our studies and links to current and former students are listed below.
Current and Former Students
Publication List of Tony Borgerding
Presentations of the Borgerding Group
Research Summary: Our research is centered on analytical measurements made using various forms of chromatography and mass spectrometry to design and apply new instrumentation that make measurements faster and more selective. In order to make these techniques work efficiently, we design novel injectors, extraction systems, and interfaces at the “front end” of the instruments, usually taking into account specific requirements of the particular measurement we need to do. We are also working on new chromatographic detectors to improve the selectivity of our measurements. For example, in the past we have built systems to measure ethanol and acetaldehyde levels in blood and heart tissue as part of cardiomyopathy studies, and monitored levels of airborne VOCs in a microbial air purification system. Our current work is focussed in three areas: 1) Characterizing and applying microdialysis probes for extraction of volatile analytes from aqueous solutions into the gas phase. 2) Performing environmental measurements of perfluorinated compounds (PFCs) using LC-MS/MS. 3) Characterizing and applying a novel aromatic selective laser ionization detector (ArSLID) for analysis of environmental pollutants.
1. Extractions to the gas phase using microdialysis probes:
General: We construct extraction probes using ~3 mm lengths of 0.2 mm i.d. dialysis membranes. By flowing helium or another gas through the probe (as opposed to aqueous buffers, which is more common) we can selectively extract volatile analytes from aqueous samples. Using microdialysis membranes is advantageous because their small size allows them to be used in very small environments such as those in biological systems, and also results in fast transport of anlytes across the membrane.
Schematic diagram of microprobe extractors
FID signal traces resulting from exposure of the microprobes to samples containing ethanol (solid line), toluene (dashed line) and butanol (dotted line) for different amounts of time. The data show the extremely fast response of the probes in reaching a steady state after exposure.
a. Measuring nitric oxide in neurochemical systems with chemiluminescence detection. Nitric oxide (NO) has been identified as a key messenger molecule various neurochemical pathways that affect brain function. The rapid transport offered by our extraction probes is vital in the measurement of NO, which has a half life of about 15 seconds in biological systems. Extracts of hte microdialysis probe are transported to a chemiluminescence detector, which is very selective and sensitive for NO. In-vivo experiments on animals will be conducted in the laboratory of Dr. Mike Bowser at the University of Minnesota.
b. Monitoring ethanol metabolism. Because alcoholism is so common, it's specific effectt on the body is studied in detail. In particular acetaldehyde, formed by oxidation of ethanol, has been identified as particularly toxic. Using fast GC, we can separate ethanol, acetaldehyde, and acetic acid (to which acehaldehyde is further oxidized) in less than 10 seconds, allowing us to monitor this process with good temporal resolution. Further work is required to characterize this reaction in vitro and in vivo.
c. Improving detection limits. Gas-phase microdialysis extraction is limited by the volatility and hydrophobicity of the analyte (roughly estimated by Henry's Law). As a result, << 1% of analytes that are relatively hydrophilic are extracted, resulting in detection limits that are ~1 mM by GC-FID. In order to improve these detection limits, we are cryogenically concentrating the gas phase extracts and utilizing more sensitive detectors.
2. Environmental Analysis using LC-ESI-MS/MS.
General: Liquid Chromatography with electrospray ionization (ESI) and tandem mass spectrometry is an important analysis tool for many water soluble environmental pollutants due to the high efficiency of the ESI process and the outstanding selectivity and sensitivity of tandem mass spectrometry. Our group is pursuing several studies that utilize our recent acquisitions of a Varian Triple Quadrupole and a Micromass QTof2.
a. Analysis of atrazine in shallow lakes. In collaboration with Kyle Zimmer of UST Biology, we are analyzing the pesticide atrazine in water and sediments from shallow lakes as part of a study to compare the presence of this compound with various biological parameters of the ecosystem.
b. Analysis of known PFCs. We are beginning studies of polyfluorinated compounds in the environment. These compounds, related to the production of stain- and stick-resistant products, are becoming ubiquitous in the environment. Furthermore, their chemical properties present a very difficult challenge in sample handling, pre-concentration, and other sample preparation. Compounds of particular importance are the polyfluorinated sulfonates and carboxylic acids.
c. Analysis of unknown PFCs. As PFCs make their way through various parts of the environment, they may be subject to changes in their chemical composition from photolysis, biodegradation, or some other environmental process. Identifying these degradation products is a very important step toward understanding the overall danger these compounds may present to the environment. The high resolution MS capability of the QTof2 provides a valuable tool for identifying unknown PFCs.
3. Selective analysis of aromatic compounds using the aromatic selective laser ionization detector (ArSLID).
General: the ArSLID is an inexpensive GC detector that we designed and constructed at UST (with collaborators at NDSU for early work). An inexpensive diode pumped laser provides 0.4 uJ of 266 nm light, pulsing at 8kHz. This is sufficient to all resonance-enhanced multiphoton ionization (REMPI), which ionizes only the aromatic compounds that absorb at this wavelength. The ions generated are focussed onto a collector wire, which generates a current that is amplified and recorded. This type of detection is much more selective than a photo-ionization detector (the traditional detector for aromatic analysis).
Schematic diagram of the ArSLID GC-detector
Comparison of ArSLID, PID, and FID for the same sample mixture containing both aromatic and aliphatic components, illustrating the selectivity of the ArSLID.
a. Measuring PAH in environmental samples. Polyaromatic hydrocarbons (PAH) are a group of compounds that are commonly regulated by agencies such as the EPA due to their toxicity, ubiquity, and persistance in the environment. A time-consuming part of typical PAH analysis is pre-treatment of these complex samples to remove compounds that might interfere with the measurement. Because the ArSLID is so selective, we hope to prove that it can simplify this analysis. The ArSLID is also being characterized in terms of how slight differences in the chemistry of the PAH may affect the intensity of their ArSLID signal.
b. Measuring total aromatic content of samples via rapid vaporization. Because the ArSLID does not detect water, analytes can be introduced to th ArSLID from samples by heating them rapidly to vaporize the volatile and semivolatile components. Chromatographic separation is bypassed, sot his analysis gives a rapid measurement of total aromatic content.
Last updated: December, 2008
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