The Stopped-Flow Method
KinTek Corporation's instruments are all designed to provide the researcher excellent results in transient state kinetic experiments. KinTek Corporation builds instruments that utilize three main methods: Stopped-Flow, Chemical Quench-Flow, and Optical Photolysis.
An experiment using a basic stopped-flow apparatus is quite simple in principle. This apparatus uses the drive motor to rapidly fire two solutions, contained in separate drive syringes, together into a mixing device. The solutions then flow into the observation cell displacing the previous contents with freshly mixed reactants. A stop syringe is used to limit the volume of solution expended with each experiment and also serves to abruptly stop the flow. The flow of solution into the stop syringe causes the plunger to move back and trigger data collection. The fresh reactants in the observation cell are illuminated by a light source and the change, as a function of time, in many optical properties (Absorbance, Fluorescence, Light Scattering, Turbidity, Fluorescence Anisotropy etc.) can be measured. The measurement of these optical properties is performed by the system's detectors, which can be mounted either perpendicular or parallel to the path of incoming light depending on in which optical property you are interested. The SF-2004 series of stopped-flows allow the mounting of three detectors (two perpendicular to and one in line with) the incident light. Data from all three detectors can be collected simultaneously.
A double mixing stopped-flow system is capable of mixing three reactants in sequential fashion to perform Double Mixing Experiments. In this more advanced system there are three drive syringes. The first two drive syringes drive two solutions together through a mixer and into a delay line. The length of the delay line along with how long it takes the solutions to pass through the delay line determines the length of the first reaction. After passing through the delay line the first two solutions (now mixed) enter a second mixer where they are mixed with a third reactant and then the mixed solutions pass into the flow cell. The reactants displace the previous contents of the observation cell and trigger data collection as described for the basic stopped-flow system. The members of the SF-2004 family of Stopped-Flows are all capable of performing both single and double mixing experiments in their base configuration.
Regardless of which configuration the stopped-flow uses, the time resolution of this method is limited by the the time required for the reactants to flow from the final point of mixing to the observation cell. This time is referred to as the dead time of the instrument. The SF-2004 series of Stopped-Flows have guaranteed dead times of less than 2 milliseconds. For all stopped-flows, the volume of the mixer, observation cell and flow lines all affect the volume of reactants that must be pushed to obtain a satisfactory reaction. The SF-2004 series of stopped-flows utilizes micro volume flow cells, lines and mixers. These micro volume devices allow the SF-2004 series of stopped-flows to push as little as 30 microliters of reactant per shot! If you wish to perform single mixing stopped-flow experiments using your own spectrofluorimeter or spectrophotometer, KinTek Corporation provides the SF-MiniMixer Stopped-Flow.