DISPERSION: A Summary
When developing an assay on a given instrument the most important parameter to adjust is the injected sample volume. If the sample volume is larger than 3 S1/2, the D value will approach 1 in a single line FI system, or in a SI system , double-humped will be obtained due to the lack of reagent in the center of the sample zone.
FI systems should be constructed using confluence points, where carrier and reagent streams merge. This avoids the formation of double peaks since reagent is supplied evenly throughout the entire length of the sample zone, while the D value increases in the ratio of flow rates.
In SI systems the radial mixing is promoted by flow geometry and flow rate changes (Chapter 2).
Increasing channel length in order to gain incubation time, is not a good choice in any system (FI or SI), since the sample zone broadens as it travels through the channel. Thus, the gain of reaction time is offset by dilution, while the sampling frequency decreases.
Instead use flow programming, including stop flow.
Sensitivity of an assay can be increased by increasing injected sample volume, but only moderately. Using a long path flow cell, elevated temperature and the use of BI technique are more efficient options.
1.2.19
