F. Moffatt et al., Capillary electrochromatography. Abnormally high efficiencies for neutral-anionic compounds under reversed-phase conditions, ANALYT CHEM, 71(6), 1999, pp. 1119-1124
Unusually high efficiencies (up to 2.5 million plates m(-1)) during the cap
illary electrochromatographic analysis of partially ionized anionic-neutral
compounds have been observed under reversed-phase conditions using a stand
ard C-18 stationary phase. An explanation has been proposed in terms of non
equilibrium conditions caused by pulses of stronger or weaker solvent that
arise from the sample. The increased efficiencies are observed when the mig
ration time of the analyte is closely matched to the elution time of sample
-induced discontinuities in the mobile phase. Repeatability and hence the f
easibility to control the system have been demonstrated along with the effe
ct that separation parameters such as mobile-phase organic solvent content,
ionic strength, and separation voltage have on peak efficiencies, areas, h
eights, and asymmetry. Van Deemter plots show that the B term (axial molecu
lar diffusion) is the only major contributor to peak dispersion. A reduced
plate height of 0.1 was obtained. The implications of this phenomenon and i
ts ability to cause concurrent electrophoretic effects during the analysis
of charged species, thus leading to even greater efficiencies, are discusse
d.