Undergraduate Research in Using Fourier Transformations

Doing research Fourier Transforms in the undergraduate environment is not a trivial undertaking. Most undergraduate students will have little or no background in the area until after their senior year. By this time, the junior summer year will be past, and an opportunity for contiguous lab time lost. The computer techniques and instrumentation involved likely will not be understood well past the introductory level, and the basic measurement techniques will be a challenge as well.

Thus, projects that I have offered here have built into them an introductory time period of at least a month while literature is studied, simple programming concepts learned, and basic measurment skills honed. Following this, there is a month of lab work, then two weeks of result analysis and poster presentation. Then the work is handed on to the next student. We work in small, connected steps!

Our initial work in using FT to study instrumental artifacts in Atomic absorption had the desired research feature of being blessed with a largely stable set of light sources (the air/acetylene flame and the hollow cathode) about which a lot was already known (compare this to the expermental horrors of working with a spark discharge train). AA also had a proven analytical track record, while still needing additional work to compensate for variable and unexpected differences between standards and natural samples. The AA instrument also was usually in a fixed lab location, even though natural samples had to be taken in the field and stored in potentially contaminating bottles while being brought to it. These problem areas comprise some of the research goals I explored in the past three summers.

From the purely instrumental perspective, my first ideas were to put an atomic absorption instrument on a cart. Included with the instrument would be a gasoline powered motor generator to run everything, and two gas cylinders, one air and one acetylene, for powering the flame. The purpose for this was to take the instrument, plus water filtration devices, to the field sites where environmental issues were to be studied, thus avoiding the problems of sample storage and transport. A set of first experiments worked nicely when the instrument was taken on the back of a pickup truck to a Sheldahl Co. lab site to follow copper and iron effluents from a disposal line.

Avoiding problems with matrix effects also is a primary research goal, since little or no sample preparation is desired when an instrument is taken into the field. This is where the Fourier Transformation work entered. I suggested that dilution with ultrapure water could be the way to compensate for variable matrices. Nathan Peitersen began this work. He and I explored using Fourier Transforms on the (supposedly) DC output signal from our Buck Scientific instrument. The first goal was to see if noise frequencies could be eliminated by zero filling in the frequency spectrum, lowering the detection limit, and allowing the samples to be diluted to a point where variations in matrix were not an issue between water standards and natural samples. Nathan discovered that here were indeed many components to the FT spectrum of he instrument output. One was a low frequency discrete component that ultimately was traced to the digital readout on the front of the instrument. Another was due to the power line leakage through the DC supplies, and its 60 Hz harmonics(labelled in green), probably due to poor filtering of the supply output. A very interesting one at 285 Hz (labelled in yellow) was due to the incomplete demodulation of the modulated output of the hollow cathode lamp. There were others that we were unable to trace to specific components in the instrument. Some of them changed with the kind of water being nebulized through the flame, making us think that they were present in the flame itself, and might even be useful for analytical work. This was moivation for continuing the project after Nate graduated.
Joe Lohmeyer picked up the research from more of a FT perspecive, and completed developing new LabVIEW Fourier Transform techniques designed to better extract information from the output of the AA instrument, and the departmental NMR instrument. He succeeded in developing an excellent set of LabVIEW Virtual Instruments that the Chemistry 378 lab students can use to explain how quadrature detection is used in the NMR experiment, following demodulation to remove the 300 MHz carrier.

A particularly rewarding aspect of his work was when he was able to acquire FID data from our Varian 300 MHz machine, store it as an Excel text file, and transfer it into his own VI to do the Fourier transformation, phasing, and final expanded scale display. The results for key compounds (i.e., compounds of particular interest in the Instrumental Analysis lab) were lovely. Joe developed a new time model for undergraduate research based on working three full afternoons a week during the second semester of the senior year, instead of (or in addition to) the junior summer session.

Joe graduated this May 28th, and was commissioned to become a degreed officer in the U.S. Marine Corps on May 29th. Here he is, with our friend, Emina Stojkovic, on that day. By any count, this is truly a unique, historic picture. Delightfully Joe came back from his tour in Iraq in one big piece!