stopped

Stopped-flow is a lab technique for studying fast chemical reactions.
A stopped-flow instrument is a rapid mixing device used to study the chemical kinetics of fast reactions in solution. The solutions are first forced from syringes into a mixing chamber. After perhaps a few milliseconds the observation cell is filled by a piston linked to a sensing switch that triggers the measuring device and the flow is stopped suddenly. The system is often modeled by conventional kinetic equations.
After two or more solutions containing the reagents are mixed, they are studied by whatever experimental methods are deemed suitable. Different forms of spectroscopy and scattering of radiation are common methods used. The dead time is the time between the end of mixing the two solutions and the beginning of observation of the kinetics of the reaction. The usual dead time of a stopped flow apparatus is 1–2 milliseconds but some new devices have been developed that have dead times of 0.3–0.6 ms.A stopped-flow instrument coupled to either a circular dichroism spectrometer or a fluorescence spectrometer is often used in the field of protein folding, to observe rapid unfolding and/or refolding of proteins.

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