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EXPERIMENTAL TECHNIQUES TO STUDY KINETICS: THE FLOW METHODS, stopped…
EXPERIMENTAL TECHNIQUES TO STUDY KINETICS: THE FLOW METHODS
EXAMPLE / APPLICATION
protein-protein interactions
fluorescence resonance energy transfer (FRET)
manufacture of detergents
protein folding, as well as enzyme, chemical or coordination reactions.
oil refining
FLOW METHOD DIAGRAM
MECHANISM
CONTINUOUS-FLOW METHOD
• The analysis can be made in the reaction mixture using an optical, thermal, electrical or other method.
• The average time, during which the reaction proceeds before an element of volume and reaches a distance d along the reaction tube, is d/v, where v is the linear velocity.
• The analysis of reaction mixture is made at different points along the observation tube and thus the progress of the reaction at different times can be obtained.
• From the measurements made at various distances, a concentration time plot can be obtained from which the rate constant can be determined.
• In this method, the two fluids (reactant) are forced into a mixing chamber and allowed to flow through a transparent tube called observation tube.
STOPPED FLOW METHOD
• Progress of reaction is monitored by using a method that has a rapid response such as oscilloscopic methods the concentration can again be studied as a function of time after the flow ceases.
• As the time progresses, the reaction mixture present at the point of observation continues to react.
• However, the flow is suddenly stopped and comes to rest (steady-state has attained).
• This method is very economical and takes advantage of rapid mixing of reagents.
• In this method, the rapidly mixed reactants emerge through an observation tube as in continuous flow method.
THERE ARE 2 DIFFICULTIES WITH FAST REACTION UNTILL WE NEED TO USE A SPECIAL TECHNIQUES TO STUDY ABOUT FAST REACTION
The time it takes to measure the amounts of substances may be comparable with the half-life of the reaction
The time takes to mix reactants or to change the temperature of the system may be significant in comparison with the half-life, so that the initial time cannot be measured accurately
ADVANTAGES FLOW METHOD
Improved process safety
Increase product quality and yield
Space saving
ADVANTAGE OF STOPPED FLOW METHOD OVER CONTINUOUS FLOW METHOD
A permanent record of the progress of reaction covering a wide range can be obtained
The method is not affected by rate and character of flow, provided the mixing is proper
A very small quantity of the reactant is required
PRINCPLE KEYS
Others than to speed up the mixing of liquids or gasses, flow techniques are typically used to study reactions occurring on timescales of seconds to milliseconds (fast reaction).
HOW IT WORKS GENERALLY
The reactants are mixed at one end of a flow tube, and the composition of the reaction mixture is monitored at one or more positions further along the tube
If the flow velocity along the tube is known, then measurements at different positions provide information on concentrations at different times after the initiation of reaction.
Introduced by Roughton and Hartridge in 1923. Reactants are mixed within a very short time span, that is why these method also known as ‘mix and shake method’
