1. Theoretical bases and principles of constant flow analysis

The term Flow Injection Analysis (FIA) was first used in 1975 by Ruzicka and Hansen [2] to designate the operation whereby a sample solution was injected into a moving fluid using a hypodermic syringe; this sample was then drawn towards a detector, a spectrophotometer in the case of a phosphate solution, or a potentiometric detector in the case of an ammonia solution.

An early example of this type of method can be found in the work of Nagy et al. [3] , where a mixing chamber placed in the path of a solution injected into a transport electrolyte enabled rapid and complete homogenization of the solution to be analyzed with the electrolyte.