Tuning Reactivity of Platinum(II) Complexes

conventional methods are classical methods such as volumetric and gravimetric
techniques that are routinely applied in standardisation of new methods.
The other method is referred to as intermittent sampling where the samples are
quenched immediately after they are withdrawn. This can be accomplished by addition
of a chemical reagent, changing the pH or temperature of the reaction mixture to stop
the reaction. 8 This method is useful for very slow reactions with a half-life in excess of
several minutes. Therefore, Conventional techniques are inadequate for very fast
reactions which take a very short period of time for the reaction to reach completion.
Fast reactions are in the range of 1 minute to 10 -14 seconds. 25 Such reactions require
automated methods such as flow-through and pulse methods. 28,29 Examples of the flow
current methods in use are UV-Vis Spectrophotometry and stopped-flow techniques and
are further discussed below.
2.4.1 Flow Methods
For fast reactions, the period for mixing varies from 10 -3 s to 10 seconds in the flow
methods. As a result, reactions whose half-lives are about 10 -2 seconds are normally
studied by the flow methods, by the continuous flow or the stopped-flow method. 30
In the continuous-flow method, first pioneered by Roughton and Hartridge 29, the two
solutions (A &B) are forced into the mixing chamber-where the reaction is initiated-by
use of pistons (Figure 2.5). The resultant mixture immediately flows out into the
observation chamber, where at some distance (d) a steady-state is attained, allowing
maximum spectroscopic detection. Since the reaction passes through a steady-state, the
observation may be a slow process. The method is also wasteful since large amounts of
solutions are required. These problems were solved by application of the stopped-flow
technique (Figure 2.6).
18