Stopped-flow is a spectroscopic technique used for studying fast reaction mechanisms in solution over timescales of about 1ms up to 100’s seconds. In general, two reagents are rapidly mixed together and then ‘stopped’ in an observation cell. The sample cell is irradiated with (usually) monochromatic light and as the reaction proceeds the change in the recorded signal, usually a fluorescence signal or the absorbance at a specific wavelength, is recorded as a function of time.

Analysis of the resulting kinetic transient can determine reaction rates, complexity of the reaction mechanism, information on short-lived reaction intermediates etc. A series of stopped-flow experiments can be used to show the effect of parameters such as temperature, pH and reagent concentration on the kinetics of the reaction.