Charles Abrams (Truman College, USA), Michael Paul Chiarelli (Loyola University, USA), Thomas Higgins (Harold Washington College, USA)
We have developed a new undergraduate experiment on the analysis of halomethanes and other disinfection by-products using GC/MS with negative chemical ionization (NCI). Halomethanes are the largest class of water disinfection by-products, produced during the chlorination of wastewater. Regulated halomethanes include CHCl3, CHBrCl2, CHBr2Cl, and CHBr3. The total concentration of all four must be below 80 mcg/L (US EPA). The detection limit under Negative Chemical Ion (NCI) mass spectrometry is 10-30 ng/L, so students can observe halomethanes at concentrations well below action levels. All four halomethanes are resolved using a 4.5 minute gradient, so samples from an entire class can be analyzed overnight using an autosampler. Students remotely connect to the GC/MS to initiate the analysis and analyze their chromatograms. Undergraduates at Loyola University, Harold Washington College, and Truman College prepared, ran, and analyzed their own samples including bottled water, filtered tap water, natural water from Lake Michigan or the Chicago River, and water from a local treatment plant. Students were asked to judge, based on their results, whether the water was safe to drink.