Continuous flow injection is a mature technique for automation of a wide variety of reagent based assays. It has also been used as a “front end” to practically all spectroscopic and electrochemical detectors, of which UV-VIS spectroscopy, Atomic Absorption and Inductively Coupled Plasma Spectroscopy are the most prominent examples.
The chief advantage of cFI is the simplicity of its experimental setup, where sample injection, reagent addition and product detection follow a clear route, travelled by continuous forward flow. That allows automated assays to be carried out even without computer control, since it is the flow generated by the pump provides strict time framework necessary for reproducible reaction conditions. Such control of the mixing and timing allows reagent based assays to be carried out reproducibly, even if the chemical reactions involved do not reach completion.
A manually operated cFI setup is still an economical option for serial assays, when funds for automated instruments are not available. It is also a best tool for teaching the principles of flow analysis in any setting, as such a simple system allows students to focus on the kinetics of physical dispersion and chemical reactions, without distraction of composing software script.
Advances in computerization have enhanced cFI, mainly through automation of data collection, calibration routines and automated sample injection. In this way a routine laboratory, with aid of an auto sampler can assay up to 120s/hour on a single instrument.
Programmable flow injection, while still in its infancy, has documented advantages compared to cFI. Enabled by advances in microfluidics, fluid propulsion and computerization it offers unprecedented versatility in optimizing reagent based assays, without need of physical reconfiguration of the flow system. Compared to cFI, the mini pFI instrument is downscaled in all parameters: it has a footprint of an iPad, uses ten time less of sample and reagents and generates a fraction of waste, since its pumps are idle most of the time. The mini pFI, similar to cFI, is compatible with a wide variety of detectors of which spectrophotometry, fluorescence and chemiluminiscence are integrated into its architecture.
In this Tutorial, pFI method has bee introduced for the first time and applied for reagent based assays. While mini pFI is less reproducible and more complex to implement then miniSI, it offers yet unexplored opportunities for development of analytical techniques that will exploit versatility of advanced microfluidic manipulations. Mini pFI and miniSI can be performed on the same instrument, that is also potentially suitable to perform separations in renewable microcolumn mode (Chapter 3)