Research by Lawrence Potts

Professor Potts and his students have been studying the detection and analysis of organic compounds in rivers and streams in the Saint Peter area. Our major analytical tool has been gas chromatography with a mass-selective detector (GC/MS). We have worked on developing reproducible sampling techniques and clean, loss-free methods of sample isolation and concentration. We are able to work with samples containing 50 parts per trillion pesticides using selected-ion monitoring (SIM) GC/MS.

The following projects are still in progress:

1) SPE and SPME preconcentration and reproducibility studies. We have used SPE (Solid Phase Extraction cartridges), SPME (Solid Phase MicroExtraction fibers), plasticizer-free tubing, sub-micron particle filtering, and ultrapure water to create a reliable system for filtering and preconcentrating pesticides. In our hands, samples at the 300-pptr levels have been reproducible at the 5-10% relative standard deviation level. We continue to work on standard addition method development and the development of suitable surrogates.

Chromatogram SIM GC/MS pesticides isolated from Minnesota River water. (Joseph Katzenmeyer, GAC '04)

2) Agricultural chemicals (herbicides and insecticides) in Minnesota River water.
Rapidly changing agricultural practices, the availability of genetically modified ("Roundup-Ready") crops, the regulation of the use of traditional pesticides, and seasonal and precipitation-variable river flowrates, make this a rapidly changing and challenging analytical system. An example chromatogram is shown below.



Chromatogram (SIM) of PFOA family of compounds, octa- through dodecyl-. (Adam Caulfield, GAC '07)

3) Analysis of PFOS/PFOAs in river water. Perfluorinated organic sulfonates and acids have been attracting attention recently. They are chemically unreactive, and so have a long life in the environment. They have been used in fabric stain guards and in the process for the Teflon coating of utensils for many decades. Most investigators have used liquid chromatographic methods to analyze samples for the family of PFOAs, but we have had some luck detecting low concentrations with SPME and SIM GC/MS. The following chromatogram shows some results (thanks to Prof. Matt Simcik at the U of Minnesota for providing standards).


Portion of chromatogram (Scan mode GC/MS) of Sheep Dip(tm) single malt scotch whiskey. SPME fiber one-minute headspace exposure. (Douglas Schroeder, GAC '08)

4) Headspace analysis of volatiles and flavors. Distilled spirits such as scotch whiskey and tequila are interesting samples containing a large number of flavor volatiles (esters). SPME, activated charcoal chips, and "Microcaps" (5 microliter capillaries) are good sampling devices for headspace analysis of flavor volatiles. We are learning more about the analytical sampling (and taste sampling) of these materials.