2.1. Flow Injection
Continuous Flow Injection techniques share the same feature: sample zone moves from injection point downstream through a manifold and flow cell by forward and constant flowrate. We open this chapter by examining a single stream configuration, where sample moves through manifold comprising injector, mixing coil, and flow cell. Limitations of this design, caused by inefficient axial mixing, will be discussed and eliminated by including into manifold design confluence point at which sample stream merges with stream of reagent. We shall see why confluence points are the key components of all FI manifolds; they facilitate addition of reagent to sample solution and promote mixing by breaking the laminar flow at a point where merging streams meet head-on.
As we shall review numerous advantages of using FI for automation of a variety of reagent-based assays, we shall also recognize drawbacks of using constant flow of reagents for transport of sample through complex manifolds. This will lead to consideration of advantages of flow programming and will serve as an opening to Chapter 3., where introduction of confluence point also leads to substantial enhancement of performance of the system.