The Dependence of the Sensitivity and Reliability of Contactless Conductivity Detection on the Wall Thickness of Electrophoretic Fused-Silica Capillaries
Abstract
A contactless conductivity detector (C4D) performance has been tested on a simple capillary electrophoretic separation in a standard fused-silica capillary with an external diameter of 360 μm and in a thin-walled capillary (an external diameter of 150 μm); the internal diameters of the two capillaries were identical, equal to 75 μm. Potassium and sodium ions have been separated in a morpholinoethanesulfonic acid/histidine background electrolyte (MES/His), over a wide range of its concentrations (0 - 100 mM).
At low MES/His concentrations, the C4D response, obtained from the height of the potassium peak, is by 100 to 200 per cent higher for the thin-walled capillary and the calibration dependences are linear, in contrast to the thick-walled capillary. These differences between the two capillaries decrease with increasing MES/His concentration, the C4D response in the thin-walled capillary is then higher by mere 20 per cent and the calibration dependences are linear in both the capillaries.
The highest sensitivities have been obtained at a MES/His concentration of 50 mM, with LOD values for potassium ion of 2.0 and 2.6 μM, in the thin- and thick-walled capillaries, respectively. The signal-to-noise ratios and the plate counts are generally similar for the two capillaries.
It follows from the results that special thin-walled capillaries can be advantageous when background electrolytes with very low conductivities must be employed