We present a laboratory experiment, suitable for implementation in analytical chemistry courses at the undergraduate level, that demonstrates the utility of time-based measurements with doublet peaks in flow injection analysis. The measurements are taken with an instrument that incorporates a simple solid-state detector, which has as its source a light-emitting diode (LED) and as its detecting element a photodiode (PD). The system studied here is a simple acid-base titration. The experiment could be adapted to any number of chemical reactions that result in a product that absorbs light of the LED wavelength significantly.