Sample Volume & Dispersion Coefficient
Increasing the injected sample volume increases peak height until a steady state plateau is reached.
Peak height increases linearly with the injected sample volume up to D=2 . The sample volume needed to reach 50% of the steady state depends on the volume, geometry and flow rates in the channel between injector and flow cell.
For conventional FI systems, S ½ value is about 50 μL, and for microSI systems, as low as 5 μL.
If the radial mass transfer is incomplete, the resulting peak shape is composed of two exponential parts as shown here. With increasing efficiency of radial mass transfer gradients are
1.2.12.
reshaped and follow an erf function, ultimately approaching Gaussian shape. (see Chapter 0.) Changing the injected sample volume is a versatile and convenient tool for adjusting the dispersion coefficient and for optimizing the sensitivity of flow injection-based assays.
The enclosed recording shows traces obtained by injection of bromothymol blue solution into 0.5 mm I.D. tubing, 20 cm long, at a flow rate of 1.4 mL/min in a single stream system. Spectrophotometry at 620nm.
