Electrophoresis at High Salt Concentration

A short study was conducted on the pH effect over a broad range, from pH 3.0 to pH 

The sodium chloride concentration was 1.5 M in all buffers. There were no observed differences in either migration times or peak shapes for I, SCN. NOr and 103 between pH 3.0,7.0, and 12.0. This effect strongly indicates that the electroosmotic flow is greatly suppressed, and the ionized silanol groups at the capillary surface are effectively shielded by the high concentration of cations, M, in the buffer solution [7]. 

Sample solutions containing low concentrations of several inorganic anions were run at pH 8.5 with increasing concentrations of sodium chloride or lithium sulfate in the BGE. The plots in Fig. 10.6 show several interesting effects. One is that the current increases rapidly with increasing salt concentration and levels out at 280 pA around 200 mM sodium chloride or lithium sulfate. This sharp increase in current can be attributed to less electrical resistance. The maximum current that can be obtained in our instrument is set at 280 pA. In order to maintain this current, the voltage was automatically lowered as the salt concentration in the BGE continued to increase. The full power of the instrument s power supply was then being used. 

The electrophoretic mobilities of the sample anions increased at the same time the current was increasing between 0 and 200 mM of added sodium lithium sulfate (Fig. 10.6). Actually, a decrease in electrophoretic mobility is predicted with increasing salt concentration. The initial increases can be explained by Joule heating. Under the conditions used a temperature of 49°C was calculated fore the capillary at high salt concentrations [6]. 

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