The most important component of flow injection analysis is a capillary with a diameter <1 mm and a length of about 1–2 m, which is continuously flowed through by a flow medium that has been mixed in advance with a reagent for the detection of the desired analyte. When an analyte solution is then injected into the capillary, during the migration of the analyte through the capillary a chemical reaction occurs between the analyte and the detection reagent; when the (now chemically modified) analyte finally reaches the end of the capillary, it is detected there by an appropriate detector and quantified on the basis of the (physico-)chemical properties of the reaction product. The actual detection/quantification can be