4.3 Samples

4.3.1 Sample Introduction

For loading a sample, a stable DC power supply of about 30kV (200-300mA) is required. Instruments are made with the ability to switch polarity to facilitate a variety of methods of operation. Usually, current is monitored and maintained to compensate for some temperature-induced changes in buffer viscosity.

Sample volumes are generally incredibly small. Volumes as low as 5µL can be sufficient for several injections. This can be disadvantageous if the sample is very dilute, because being limited on the loading volume of a dilute sample can reduce sensitivity. Loading too much of a sample can result in bad peak shapes due to field inhomogeneities if the conductivity of the sample is different from that of the buffer. Additionally, if the injection length is greater than the diffusion-controlled zone, peak broadening will occur.