Flow Injection Analysis in Industrial Biotechnology

Flow injection analysis (FIA) is an analytical chemical continuous-flow (CF) method which in contrast to traditional CF-procedures does not rely on complete physical mixing (homogenisation) of the sample and the reagent(s) or on attaining chemical equilibria of the chemical reactions involved. Exploiting controllable dispersion of the injected sample within the reagent-containing carrier stream and strictly reproducible timing of all events taking place, it is based on measuring transient signals, which not only implies very high sampling rates, but also, and most importantly, permits implementation of a number of novel methodologies which are not feasible when performed under batch conditions or by conventional CF-procedures. Demonstrated for selected bioanalytical and technological applications encompassing cellular and enzymatic assays as well as monitoring of culture media, the principles and operational characteristics of FIA are first outlined, and then its downscaled/miniaturized sequels, that is, sequential injection analysis (SIA) and lab-onvalve (LOV), are detailed. Thus, in SIA the sample and reagents are, via the use of a multiposition valve and an attached syringe pump operated under full programmable control, aspirated sequentially and then propelled forward allowing the sample and reagent(s) to be intermixed and, if called for, subjected to appropriate treatments before analyte detection. This infers that merely minute sample/reagents volumes are consumed, hence leading to generation of small amounts of waste. In LOV this downscaling is taken further by using a small monolithic structure within which all sample manipulations and ultimate analyte detection under programmable control can be effected. Even bead-materials with different surface groups/characteristics, including live cells, can be handled and utilized as demonstrated. Because the syringe pump in SIA and LOV can be used for accurately aspirating, propelling or even stopping the flow, these modi operandi allow fully to exploit the interplay between the kinetics and the thermodynamics of the chemical reactions involved, so that there are no restrictions whatsoever as to the chemistries that can be implemented, even if they entail multi-step reactions. Representative bioanalytical examples of this interplay are presented.