In this laboratory experiment, students quantitatively determine the concentration of an element (mercury) in an environmental or biological sample while comparing and contrasting the fundamental techniques of atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry (AFS). A mercury analyzer based on sample combustion, concentration of mercury by gold amalgamation, and AAS is coupled to a mercury-specific AFS system, allowing for the same sample to be carried through the two systems. This provides a direct and accurate comparison between the methods that is readily understandable by students. By calculating figures of merit for each technique, including the method detection limit, sensitivity, dynamic range, precision, and accuracy, students gain a better understanding of each quantity, and how they can be used to compare instruments and select the most suitable method under particular circumstances. Following an inquiry-based pedagogy, students determine mercury levels in solid samples (e.g., soil, leaves, fish, hair, tobacco, etc.) that they choose, collect, and analyze directly, without time-consuming and potentially hazardous hot-acid digestions. Overall, the lab promotes critical thinking about performance characteristics of different instruments and environmental analyses and is suitable for an instrumental analysis or environmental chemistry course. (Contains 7 notes, 2 tables, and 7 figures.)