Need For A Coating

As previously discussed, a fused silica capillary becomes ionized above pH 2.0, making it difficult to eliminate the undesirable interactions of the surface silanol groups with analytes, such as proteins. These undesirable interactions result in poor peak shapes, loss of efficiency, lack of resolution, and irreproducible separations. Since proteins, being made of amino acids, are amphoteric in nature and vary substantially in pI, it becomes difficult to tailor separations by optimizing only the pH. In addition, operating at extremes of pH is undesirable for many proteins. Another serious limitation of operating with uncoated fused silica capillaries is that the EOF is irreproducible. This limitation can be exaggerated when analyzing proteins, since they can interact with and modify the capillary surface and, consequently, the EOF properties. To overcome these limitations and allow operation under physiological pH, numerous researchers have investigated various coatings and chemistries (11-25).

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