Dispersion measurements on conventional and miniaturised HPLC systems

Summary

The volume dispersion produced by a number of commercial detector/injector (DI) system and of laboratory designed detector/injector systems has been measured by three different techniques: (A) by direct connection of injector to detector using a "zero-length" column; (B) by measuring the plate number N as a function of capacity ratio, k′; (C) by placing a 2m × 100µm bore straight open tube between injector and detector, and subtracting the contribution from the tube according to the Taylor-Aris equation. Setting as a criterion of adequate performance that there should be less than a 10% loss in plate efficiency due to the DI system for an unretained solute peak, it is found that in general the commercial systems examined show excessive dispersion in relation to the types of column for which they are claimed to have been designed. A 1µl flow cell designed in our laboratories offers a standard deviation below 1µl and is a possible candidate for use with miniaturised systems. However, extreme precautions to avoid extra-column dispersion must be taken. The column must enter into the detector cell and injection must be by flow splitter. It is considered unlikely that current HPLC technology can be adapted for use with high efficiency columns of bore below 2mm.