P752: Drugs in the water, parts I and II
Triclosan – how much, how bad, how to make it go away?
From the compound to save us from all harmful bacteria to possibly something causing more problems than it solves, triclosan, the principle ingredient in most antibacterial soaps, has undergone a radical shift in its perception and uses. As part of a larger general chemistry semester long project in the general chemistry lab looking at drugs in the drinking water, a two-week lab has been developed. This looks at not only an assay of triclosan in soaps but follows up by quantifying the toxicity to single cell bacteria (in our integrated chemistry/biology program) or investigating activated charcoal as a means of removal of triclosan from solution. The lab is based around a reaction in which triclosan forms a diazonium ion (illustrated below) and uses UV-Vis spectroscopy for the assay. While the first of the two labs follows a simple quantification model, we have students work in sections preparing common solutions and working as part of a larger team. In the second week, as we move to study the adsorption by charcoal, each of the 8 lab sections form part of a bigger team with work from preceding sections being built upon throughout the week and students designing and implementing their experiments along with sharing the data with their peers. This also requires students to coordinate work within their section to ensure quality data is collected reinforcing concepts such as controls and reproducibility.
Why does it keep changing? Sulfa drugs vs pH
At Concordia College, students undertake a 7 week research project as the culmination of the general chemistry laboratory program looking at ways to degrade sulfa drugs in aqueous solution. While the sulfa drugs display strong absorbances in the UV-region of the spectrum, making UV-Vis spectroscopy a viable measurement technique, this is complicated by a variation in the speciation of the sulfa drug with respect to pH (shown below). Each of the three forms possesses a different spectrum and so students commonly mistake the change in the spectrum of a solution due to minute variations in pH for a real degradation. To combat this problem, we developed a lab which has student groups record spectra for all pH values between 2 and 12 and create a spectral overlay which clearly shows the variation with pH. This lab synchronizes well with the acid-base theory being taught in lecture at the time, provides an introduction to the preparation and handling of solutions of the sulfa drugs and also aids in learning how to prepare and present spectral data. Most importantly, it ensures when students go to start their research project that they are collecting quality data, seeing real degradation where it occurs and not mistaking the artifacts arising from pH change for a false positive.