We have demonstrated above a significant improvement in selectivity for Trp oxidation over that for Tyr with the optimized MSW (Figure , -0.2 V holding, +0.7 V transition, +1.1 V switching, 2 ms duration of switching potential, 600 V/s scan rate between the transition and switching potentials). We then wanted to assess whether the presence of Tyr in the same solution would affect the Trp signal in any way. Thus, we performed injections of a mixture of 1 μM Trp + 1 μM Tyr into the FIA and compared/contrasted that current density with those of Trp and Tyr alone (Figure ). We observed that while there is a significant drop in Trp current density as a result of the presence of an equivalence concentration of Tyr, the current density is still significantly higher (4-fold) than that for Tyr alone. We hypothesize that this decrease is not due to the oxidation of Tyr at the electrode surface (since it's relatively small) but merely the shielding of Trp from interacting with the electrode by the presence of Tyr. Next, we tested whether other common interferents such as dopamine and serotonin would affect the Trp signal. As seen in Figure , while the presence of dopamine and serotonin did shift the Trp peak slightly, dopamine and serotonin oxidation were observed at a much lower potential than that for Trp oxidation so interference was negligible.