Counterflow Isotachophoresis−Capillary Zone Electrophoresis on Directly Coupled Columns of Different Diameters

Counterflow isotachophoresis−capillary zone electrophoresis (ITP−CZE) on directly coupled columns of different diameters was explored to increase the injection volume and lower the detection limits in CZE. A solution of neostigmine bromide and propantheline bromide was used to evaluate the system; the relative standard deviations for four injections of 3.3 μL of 0.1 μM neostigmine bromide and propantheline bromide were 1.4 and 4.0%, respectively. The correlation coefficients for volumetric calibration curves over the range of 1.7−8.3 μL of the neostigmine bromide and propantheline bromide solution were 0.9979 and 0.9975, respectively, and a 2.5 nM solution could be detected easily from 8.3 μL of sample. Approximately 40 min was required for focusing.