Perhaps the most frequently used rapid kinetics techniques is stopped-flow. Small volumes of solutions are rapidly driven from syringes into a high efficiency mixer to initiate a fast reaction. The resultant reaction volume then displaces the contents of an observation cell thus filling it with freshly mixed reagents. The volume injected is limited by the stop syringe which provides the “stopped-flow”. Just prior to stopping, a steady state flow is achieved. The solution entering the flow cell is only milliseconds old. The age of this reaction volume is also known as the dead time of the stopped-flow system. As the solution fills the stopping syringe, the plunger hits a block, causing the flow to be stopped instantaneously. Using appropriate techniques, the kinetics of the reaction can be measured in the cell.
Traditionally stopped-flow has lent itself to UV/Vis detection methods – both by absorption and fluorescence spectroscopy and these are still the most common methods employed. TgK Scientific offer a comprehensive range of stopped-flow equipment from simple stopped-flow mixing accessories that can be used with existing absorbance and fluorescence spectrometers to complete, self-contained computer controlled stopped-flow systems with dedicated acquisition and analysis software.
Mixing options for stopped-flow include multi-mixing (also known as double mixing or sequential mixing) where more than two solutions are mixed together, variable ratio mixing using different size syringes and micro-volume mixing for applications where only very small quantities of reactants are available.
The environment of the reagents is also extremely important and so equipment is available for anaerobic applications, sub-zero temperature and high pressure stopped-flow applications. An extensive range of software packages is also available for the interpretation and analysis of the kinetic data. In addition to equipment for absorbance and fluorescence measurements, Hi-Tech offers dedicated stopped-flow systems including conductivity and FT-IR measurement.
Research Stopped-Flow instruments include:
Single and Double Mixing Micro Stopped-Flow Spectrometers
Conductivity accessory for a Stopped-Flow instrument
A dedicated standalone conductivity instrument
SFA-20 Rapid mixing accessory for UV-Vis/Flu spectrometers
High Pressure Stopped-Flow Spectrometer
Stopped-flow for FT-IR