We then assessed how the different waveform parameters above can be utilized to optimize for selectivity of Trp over Tyr signal. This is of particular interest as Trp and Tyr has a maximum oxidation peak at the same potential (~1.0 V) in an FSCV experiment on a CFM vs. Ag/AgCl. We injected boluses of 1 µM Trp and, separately, boluses of 1 µM Tyr into the FIA system and evaluated their respective current densities at 1.0 V vs. Ag/AgCl. Unless otherwise stated we tested 3-5 electrodes per condition. Then the current density from Trp oxidation peak was divided by that for the Tyr oxidation peak from the same conditions to yield a Trp:Tyr selectivity ratio. We observed that a holding potential of -0.2 V yielded the highest selectivity ratio for Trp:Tyr (Figure ). Now this optimal condition for selectivity differed from that for optimal holding potential for sensitivity (vide supra). Because the loss in selectivity (-50%) going from -0.2 V to -0.3 V holding potential was significantly greater than the gain in sensitivity going from -0.2 V to -0.3 V (+3.8%), we decided to select -0.2 V as the optimal holding potential overall. Moreover, we observed that a transition potential of +0.7 V yielded the highest selectivity ratio compared to those of smaller values (Figure ). The optimal transition potential for sensitivity was determined to be +0.6 V (see above). The loss in selectivity (-87%) was significantly greater going from +0.7 to +0.6 V than the gain in sensitivity from +0.7 to +0.6 V (+27%).Thus, the optimal transition potential we selected was +0.7 V.