Almost all FI systems use confluence points to add reagents and to mix them with the sample zone (Chapter 1) In order to demonstrate the efficiency of this approach, which is the cornerstone of the success of FI technology, two movie clips are shown here.
In the first clip (A) a sample zone of an indicator (bromothymol blue) in 0.01M borax solution (pH=9.2) is pumped throughout the spiral coil, passing the confluence point, at which no reagent stream is being added.
In the second clip, (B) the same experiment is repeated, while at the confluence point 0.1M acetic acid (pH=3.3) is added, at an equal flow rate. The indicator (pk =7.4) changes the color from yellow to blue, at the rate of mixing, since neutralization reactions are very fast. The following coil could be entirely eliminated as reaction is completed within seconds. Indeed, high throughput FI system operate in this fashion (Ch 1.2.26)