Programming the Flow Rate
Since mixing in a radial direction at a confluence point is instantaneous, we now need to consider the residence time available for chemical reactions in norder to produce a desired concentration of species to be monitored by a flow-through detector. Since for serial assays it is desirable to achieve a sampling rate of at least 1 s/min, the residence time of a sample in the flow channel is limited to 60 seconds unless the purpose of the assay is to reach high sensitivity and low detection limit (LOD) – the usual trade off of all chemical assays.
Surprisingly and fortunately, a vast majority of chemical reactions applied to (bio) and chemical assays will convert a sufficient amount of target analyte into a measurable species within 30 seconds or less - even at a room temperature.
This is why almost all FI systems which have been designed so far, operate on a simplest, constant flow rate platform, where the resident time of the sample zone is empirically adjusted by a combination of flow rate and the combined length (and volume) of cdhannel between injector and detector.
Yet constant flow rate is not the most efficient approach, and therefore flow programming is in this Tutorial presented with goal to inspire development and application of pFI based systems, where the length of the channel is minimized, where flow programming focused on the use of very low flow rates with reduce reagent consumption and waste generation.
Another option, stopping the flow, has not much been used in FI format, although its use is prevalent in SI mode, the reason being that FI systems use peristaltic pumps, which are not as suited for stop/flow operation, as syringe pumps used in SI instruments. This may very well change if a more suitable pump will be used.
1.2.20.
