ICP-MS Analysis of Mercury in Fish: Exploration of Method Validation, Matrix Effect, and Kinetic Energy Discrimination

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful analytical technique that can quantify elements of interest at parts-per-trillion concentrations. In this laboratory class, students performed ICP-MS analysis to quantify mercury concentration of standard reference material (SRM) 1947 (Lake Michigan fish tissue) and canned tuna from a local supermarket. These two samples were digested in two different matrices (HNO3/ H2O2 or HNO3/HCl/H2O2) and then analyzed using no-gas mode or helium mode with two different kinetic energy discrimination voltages (2V or 4V). The inclusion of HCl in the matrix produced more accurate results and stabilized mercury over the 8-day period after the digestion. Based on their analysis, the students were asked to draw their own conclusions about what they perceived to be the most accurate representation of the true mercury concentration of the tuna samples. This laboratory class provides students with a wide range of scientific concepts to explore such as method verification with SRM, kinetic energy discrimination, matrix effect, and trace metal stability over time.