No abstract

No abstract

Unusually high efficiencies (up to 2.5 million plates m -1 ) during the capillary electrochromatographic analysis of partially ionized anionic-neutral compounds have been observed under reversed-phase conditions using a standard C 18 stationary phase. An explanation has been proposed in terms of nonequilibrium conditions caused by pulses of stronger or weaker solvent that arise from the sample. The increased efficiencies are observed when the migration time of the analyte is closely matched to the elution time of sample-induced discontinuities in the mobile phase. Repeatability and hence the feasibility to control the system have been demonstrated along with the effect that separation parameters such as mobile-phase organic solvent content, ionic strength, and separation voltage have on peak efficiencies, areas, heights, and asymmetry. Van Deemter plots show that the B term (axial molecular diffusion) is the only major contributor to peak dispersion. A reduced plate height of 0.1 was obtained. The implications of this phenomenon and its ability to cause concurrent electrophoretic effects during the analysis of charged species, thus leading to even greater efficiencies, are discussed.

SummaryThe applicability of capillary electrochromatography to the automated analysis of pesticides and phthalate esters that are of environmental concern was assessed. Reversed phase packing materials were compared. Column to column and run to run reproducibility was established. Peak height with an internal standard gave the best reproducibility. Faster analysis than alternative HPLC methods was demonstrated for a mixture of the insecticide pirimicarb and related pyrimidines. The relationship between the concentration of an analyte in a sample and at the detector was determined by the use of radio-labelled 14C-pirimicarb. The volume fraction of the liquid zone was 0.64. The possibility of electroosmosis through the pores is discussed with reference to the Rice-Whitehead model for electroosmotic flow in a capillary. A new parameter, the effective pore size is used in equations for electroosmosis through porous packings.

No abstract