Valves and flow injection manifolds: an excellent marriage with unlimited versatility

An overview of the functions of valves—both injection and selection valves—in flow injection (FI) for manipulating the manifold as a function of both necessities and imagination of the user is reported. The use of single valves for sample or reagent injection, for housing different devices (namely, minicolumns and other separation units, flow-cells, etc.) is discussed. Multiple injection valve arrangements (in-series, in-parallel and inner coupling) that give place to FI modes as merging-zones (both symmetrical and asymmetrical), trapping-zone and nested-loop approaches are exposed. The possible locations of selection valves in the FI manifold are presented and the problems each design can solve are commented.