RECENT RESEARCH EFFORTS AND COMPLETED PROJECTS
Overview: My research interests seem to fall in one of 3 areas: 1) Atmospheric Aerosols, 2) Capillary Electrophoresis and 3) Chemical Education.
1) Atmospheric Aerosols: Nanometer to micrometer sized particles that are present in the atmosphere are believed to alter earth's radiative balance by scattering and absorbing solar radiation. If these particles increase the net reflectivity of the planet, they lead to a cooling effect on climate which could offset the greenhouse effect to some extent. Unfortunately, current estimates of exactly how these aerosol particles may affect climate are highly uncertain. A recent estimate suggests aerosols may offset the radiative forcing of greenhouse gases by 20 - 110%. In order to contribute to a broader effort of reducing the uncertainty associated with these estimates we work to develop new analytical methods to measure the light scattering and light absorbing properties of aerosol samples.
2) Capillary Electrophoresis (CE): CE is a microvolume separation technique based on the differential rates of migration of ions under the influence of an electric field. The technique has gained popularity as it can provide highly efficient separations quickly. My interest mainly lies in understanding fundamental factors which lead to broadening of zones in CE separations, new detection schemes, and new applications of the technique.
3) Chemical Education. In recent years many of my projects have fallen in this arena. I enjoy developing simple and inexpensive ways to either modify (improve) or build instrumentation used for chemical analysis. These modifications or instruments are completed using inexpensive, easily obtained components and the resulting publications serve as "how to " manuals to be used by other instructors in high schools / small colleges across the nation.
CAVITY RING-DOWN LOSSMETER USING AN LED.
The SSRP program provided funding for Kyle Myers to work with Prof. Thompson during the Summer of 2006 to develop a new mode of a technique termed cavity ring-down spectroscopy (CRDS). In this technique, light from an LED is introduced between 2 highly reflective mirrors, then the LED is quickly turned off. Several on / off cycles are shown in figure A below. Since the mirrors involved are highly reflective, the light continues to travel between the mirrors for a few microseconds after switching off the LED. A plot of light intensity in time after switching off the LED yields an exponential decay curve as shown in the figure on the lright below. The time constant (tau) of this decay is the measureable variable in a CRDS experiment. While we have initially applied this instrument only to the measurement of absorption by gaseous ozone and molecular iodine, we anticipate the instrument may be of significant insterest commercially. You can learn more about this experiment by reading the manuscript describing this project that appears in the journal Measurement Science & Technology.
This project was featured in a recent issue of Laser Focus World magazine (read about it HERE).
W-ICOS.
During 2005, Heather Spangler and Prof. Thompson worked to develop a new technique termed Tungsten Source Integrated Cavity Output Spectroscopy (W-ICOS). In this technique, light from a tungsten lamp was spectrally filtered and reflected between 2 highly reflective mirrors. On each pass between the mirrors a small fraction of light passes through the mirror and can be detected by a photomultiplier tube. This is the measureable signal in W-ICOS. The intensity of this light is inversely related to the extinction coefficient (kExt) of the sample which is placed between the mirrors. We have used this instrument to monitor the extinction coefficient of ambient air the evening of July 4, 2005 (Figure below). As illustrated, the extinction coefficient increased shortly after sunset. We have attributed this to fireworks displays in the area and / or the qualitative observation of a fog being present in Kearney this evening. This work has recently been published in the journal Applied Optics.
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INEXPENSIVE C.E. INSTRUMENT
We recently developed an instrument for capillary electrophoresis with fluorescence detection that costs approximately $700 to build. Commercial instruments for CE can cost > $20,000 so a significant savings is achieved. Our device was used to perform a separation of two fluorescent compounds: riboflavin and fluorescein inside of a 75 micrometer diameter capillary tube. Limits of detection for these compounds were estimated to be approx. 10 fmol. A manuscript describing this project has been accepted to the Journal of Chemical Education.
MODIFICATIONS TO THE SPECTRONIC 20 SPECTROPHOTOMETER
We have recently published two papers in the Journal of Chemical Education that describe simple modifications to using the Spectronic-20 spectrophotometer. It is my impression that nearly every chemistry major over the past 30 years has at some point used a Spec-20 instrument. These instruments are inexpensive and robust making them a perfect match for the teaching laboratory, however, a common frustration with the instrument is the time required to collect an absorption spectrum. This can take up to an hour of repetitive lab work (blank, measure sample, change wavelength). In a recent paper published in the Journal of Chemical Education we have described a simple modification to this procedure which allows an absorption spectrum to be collected in a matter of minutes.
In a related publication, we developed a water-jacketed cuvette to use with the Spec-20. This cuvette is used to thermostat a sample on which the absorption measurement is made. We applied this cuvette to making measurements of the activation energy (Ea) for the reaction between crystal violet and hydroxide. We accomplished this by measuring the rate constant for the reaction (k) at different temperatures and preparing an Arrhenius plot shown on the right below. The slope of this plot equals - Ea / R where R = 8.3145 J / mol K. This allows us to compute an activation energy of 62 kJ / mol for this reaction.
