Kinetics and Pathways of the Aqueous Photolysis of Pharmaceutical Pollutants: A Versatile Laboratory or Remote Learning Investigation

Abstract

In this laboratory experiment, students explore the aquatic photochemical fate of ranitidine and cimetidine, two common wastewater-derived pharmaceutical pollutants. It provides an engaging environmental context for students to develop knowledge of reaction kinetics and photochemistry, as well as skill 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 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 threeto five-hour lab periods while the advanced modules require additional time. This experiment requires only a HPLC, inexpensive chemicals, and common glassware and lab equipment if performed in person, and a personal computer if performed remotely.

Photochemical Reaction Made Simpler for Undergraduate Laboratory

“…Tran et al designed a candid and cost-effective apparatus consisting of a UV–visible absorption spectrometer and a high power UV–visible light emitting diode to demonstrate the chemistry of a light induced reaction in the laboratory . Many other studies like color change of the solutions of ferric chloride, 2,2′-bipyridine, and sodium pyruvate in the presence of light, photochromism by preparing open and closed isomers of a donor–acceptor Stenhouse adduct, and photochemical degradation of pharmaceutical pollutants present in wastewater are reported and planned for undergraduate students in the laboratory. − …”

Multichannel Feeding Module-HPLC Integrated System for Online Species Tracking and Kinetic Analysis

“…To date, the related literature reported by this journal mainly focused on the separation of the mixtures by a commercial HPLC. Just a few reports referred to the determination of kinetic parameters by a standard chromatograph, where manual sampling was needed. − The autofeeding of solution in previous reports mostly concentrated on the optimization of synthesis conditions, or monitoring the biological reactions by having to transfer the sample to a vial before injection by the autosampler. − However, our upgraded system could perform automatic online analysis and kinetic tracking for multiple samples with additional advantages: (1) it ensures nearly isothermal and homogeneous conditions for the reaction solutions; (2) it allows online monitoring of reactions with gas bubbling (such as N 2 , air, and so forth) or light interference; (3) it decreases the possibility of cross-contamination between different solutions; and (4) it makes users acquire plenty of real-time kinetic data under unattended operation. More than that, the integrated equipment can easily be assembled based on an ordinary commercial HPLC by changing the flow path system operated through electronic control technology.…”

Pivoting to Remote Learning: An Inquiry-Based Laboratory Closed Gaps in Self-Efficacy and Science Identity Between Students from Underrepresented Groups and Their Counterparts

“…Even before the pandemic, remote curricula have been on the rise, in conjunction with improvements in instructional technology, but have grown sharply since the widespread closing of in-person courses in the beginning of 2020. Educators from various disciplines in chemistry have made the transition from in-person to remote learning. − The general approaches used in remote laboratory courses also varied widely. Some provided students with information ,, and asked them to interpret the results.…”

“…Educators from various disciplines in chemistry have made the transition from in-person to remote learning. − The general approaches used in remote laboratory courses also varied widely. Some provided students with information ,, and asked them to interpret the results. Others provided the students with modeling software and had students develop theoretical chemistry skills, while others even went as far utilizing virtual reality to give students a more in-person experience during a remote semester .…”