Flow Injection Fluidics
Upon acceleration the injected zone disperses within the carrier stream, forming a parabolic profile  (0.3.6). The thus formed concentration gradient expands axially as it passes through a mixing  coil. This process is  visualized here by injecting a blue dye, which  is shown to form a typical concentration gradient,  as it flows through a coiled tube. A colorimetric monitoring of this concentration gradient yields a response curve, which is the result of axial and radial dispersion of the initial square impulse. Note that this Residence Time Distribution curve (RTD)  does not provide information on underlying mechanism of the dispersion  processes, since it  depicts the flow system as a “black box”.  Note that the tracer dye method is applicable not only  to cFI but also to pFI and SI, since all these techniques share the same underlying fluidic principles.  Consequently the principal parameters such as S1/2, t etc. derived from RTD, are suitable for optimization of the dispersion  process for all flow injection techniques (Chapter 0).