Flow rates vary from zero to hundreds of nanoliters per minute. However, limitations on sample injection volumes create significant demands on detection technology. An advantage of on-line separations is that a large number of spectra can be used to detect weak signals. Ordinarily, the CE separation moves charged particles to the electrospray component of the MS faster than the electrospray unit can produce gas phase ions. Smaller diameter capillaries do not lead to increased sensitivity because analytes must form droplets to elute from the capillary.
Electroosmotic flow is much more stable if the tubing is etched to form a conical end.
Among the MS technologies that can be interfaced with CE, the standard is triple quadrupole technology. An advantage is that isotachophoresis focuses like isoelectrofocusing, using leading and trailing electrolytes to bracket the electrophoretic mobilities of the compound of interest. Capillary isoelectrofocusing can be combined with ESI-MS, because the ampholyte does not compete with the sample during the electrospray process. A microdialysis junction can be used with a countercurrent flow of ammonium acetate to clean up a sample for electrospray. Solution conditions can be modified to enhance or reduce non-covalent interactions before electrospray.