Natural Resources and the Environment
College or School
Faculty Research Advisor
Second Faculty Research Advisor
The Grandy Lab is the first laboratory in the United States to adopt an amino acid (AA) pool dilution method to determine the gross rates of AA depolymerization and consumption within soils. These processes are critical in understanding the flux of nitrogen (N) between stable organic matter and biologically available mobile fractions of N. The lab is currently in the process of optimizing sample preparation steps to maximize recovery and processing time. Specifically, inconsistent recovery has been observed between soil extraction and gas chromatography–mass spectrometry (GCMS) analysis. We hypothesize loss is most likely associated with sample extract evaporation and derivatization steps. Two experiments were conducted to assess losses associated with these steps.
The first experiment assessed analyte loss during extract concentration. This technique applies a constant stream of nitrogen gas (with or without heat) to reduce the sample volume and concentrate the analyte. If AA recovery is related to length of time in the heated nitrogen dryer, then reducing drying time will result in increased recovery in the heated samples. To evaluate the correlation between evaporation rate and AA recovery, I controlled the amount of time the samples spent under the nitrogen dryer by consistently checking for completion of drying with a minimum amount of drying time allowed in one experiment and allowed two times the minimum amount of drying time allowed in a second experiment. My control set of samples was evaporated at room temperature under the nitrogen gas stream. Then I added heat to the drying block during the blow down process to increase the rate of evaporation. I controlled the height of the dryer needles, flow of nitrogen, and temperature of dryer block in both trials.
The second experiment assessed analyte loss during derivatization. Sample derivatization applies a reactive derivatizing agent to the sample in order to transform the analyte into a chemical compound that is amenable to GC analysis. This is an extremely exothermic reaction and can potentially lead to sample spatter and spray out of the container. If AA recovery is related to loss of solution from the vessel when a chemical reaction occurs during the blow down and derivatization steps, then using a vessel with greater volume will result in changes to AA recovery in the heated samples. To evaluate the correlation between solution loss and AA recovery, I used a 25ml conical vial during the blow down and derivatization steps to increase surface area and eliminate splash out during the application of nitrogen gas stream and the addition of reactive chemicals in derivatization.
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DeVries, Diane; Greenwood, Scott; and Grandy, Stuart, "Comparing Amino Acid Sample Recovery for Heated vs. Non-heated N2 Reduction (An Amino Acid Method)" (2019). Undergraduate Research Conference (URC) Student Presentations. 433.