In this laboratory experiment, students explore the aquatic photochemical fate of ranitidine and cimetidine, two common pharmaceutical pollutants found in wastewater. It provides an engaging environmental context for students to develop knowledge of reaction kinetics and photochemistry as well as skill in using analytical instrumentation. This versatile experiment consists of two basic modules, three optional advanced modules, and additional add-ons that may be performed in various combinations to meet the unique learning objectives of general, analytical, physical, and environmental chemistry courses and science outreach activities. It may be performed as a traditional lab experiment or as an entirely remote exercise with an increased focus on data analysis and interpretation using provided example data sets. All of the photolysis experiments are carried out by preparing solutions of ranitidine or cimetidine in various matrices, irradiating the samples, and periodically removing subsamples for HPLC analysis of the compound of interest. Pseudo-first order kinetic plots are then generated to determine rate constants that are used to draw conclusions about photolysis pathways or to calculate additional kinetic parameters. In the two basic modules, cimetidine is found to degrade appreciably only when irradiated in the presence natural organic matter (NOM), indicating an indirect, photosensitized degradation pathway. In contrast, ranitidine degrades in pure buffer and in the presence of NOM with comparable rate constants, highlighting the predominant role of direct photolysis. In the advanced modules, students calculate ranitidine direct photolysis quantum yields and examine the significance of singlet oxygen as a photochemically produced reactive intermediate. The two basic modules may be completed in two 3 hour lab periods, while the advanced modules require additional time. This experiment requires only an HPLC instrument, inexpensive chemicals, and common glassware and lab equipment if performed in person and a personal computer if performed remotely.
Bibliographical noteFunding Information:
The initial experiments that form the basis of the experiment were supported by the National Institutes for Water Resources/USGS National Water Quality Competitive Grants Program (W.A.A. and K.M.). The formulation of the outreach protocol was supported by the U.S. National Science Foundation (CBET 0967163 to W.A.A. and K.M.), and the formulation for more advanced students was also supported by the U.S. National Science Foundation (CBET 1434313 and 1434148 to D.E.L. and W.A.A.) and the Swiss National Science Foundation (Grant 200020_188565 to R.O. and S.B.P.). Support for the writing of this article through a J. S. Braun/Braun Intertec Visiting Associate Professorship in the Department of Civil, Environmental, and Geo- Engineering at the University of Minnesota is gratefully acknowledged (J.M.B.). We thank Dr. Kristen J. Skogerboe and Stephanie Remke for implementing initial versions of this experiment and providing useful feedback.
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- Analytical Chemistry
- Distance Learning/Self Instruction
- Environmental Chemistry
- First-Year Undergraduate/General
- Laboratory Instruction
- Physical Chemistry
- Second-Year Undergraduate
- Upper-Division Undergraduate