Continuous flow assay techniques allow for a reaction’s progression to be captured throughout the reaction. This is through the use of CCD detectors (similar to a camera) and linear observation cells.
Stopped flow assay methods allow a reaction to progress for a defined period of time before adding a quenching agent. This stops the reaction, allowing the progression to be determined, by using a secondary assay (such as spectrophotometry), at that specific moment in time. Multiple assays can be done, allowing different time intervals to be observed and the reaction progression plotted.
A limitation of continuous flow assays is the length of the observation cell. This could limit the window of time able to be studied. Stopped flow assays study the reaction of interest at a specific point in time, so it is not possible to obtain continuous data.
Both reactions have a dead time – the period of time during which no / inaccurate data cannot be obtained. It may be possible to use equilibrium perturbation techniques (such as flash photolysis) to overcome this, and the first millisecond of the reaction needs to also be understood.
Both techniques are suitable for fast reactions, allowing rapid collection of data after starting the reaction. This is through the use of pneumatic rams for the quick mixing of reactants, and computer control.