Capillaries competing ions

The negative charge of silanols can be minimized by utilizing competing ions, such as salts, amines, or zwitterions. The tailing peaks frequently observed with fused silica capillaries can be sharpened by increasing mobile phase salt concentration to 100 mM or more. However, the limitation of this approach is that joule heating increases in direct proportion to the ionic... 

In the sheath liquid approach the column effluent is diluted by the sheath liquid and hence it results in a lower sensitivity compared to the sheathless interface. Moreover, ions in the sheath liquid compete with the analytes for the transport of charge during the electrospray process, again resulting in a loss of sensitivity [62], Finally, because the sheath liquid technique involves the input of additional solvents and other chemicals, the potential to add significantly to the background noise exists. However, the use of a sheathless CEC—ESI-MS interface implies the need for specialized capillary and electrospray hardware, and thus is not as popular as the sheath liquid interface. 

In the past, the most common method of analysis of small anions has been ion-exchange chromatography. For cations, the preferred techniques have been atomic absorption spectroscopy and inductively coupled plasma emission spectroscopy. Recently, however, capillary electrophoretic methods have begun to compete with these traditional methods for small ion analysis. Several major reasons for adoption of electrophoretic methods have been recognized lower equipment costs, smaller sample size requirements, much greater speed, and better resolution. 

Dasgupta et al. [22] as well as Avdalovic et al. [23] independently succeeded to miniaturize a conductivity cell and a suppressor device down to the scale required for CE. Since the sensitivity of conductivity detection does not suffer from miniaturization, detection limits achieved for totally dissociated anions and low molecular weight organics compete well with those of ion chromatography techniques. Thus, capillary elechophoresis with suppressed conductivity detection can be regarded as a complementary technique for analyzing small ions in simple and complex matrices. 

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