The Controlled Flow™ CE capillary is made from a standard bare fused silica CE capillary but has an inner coating which is covalently bonded with a neutral polymer that has a controlled amount of sulfonic acid groups bonded to it. These sulfonic acid groups are always 100% ionized regardless of the pH of the buffer so the flow is independent of the buffer. The EOF is robust and stronger than that produced by bare fused silica because the sulfonic acid groups produce a more dense negative charge. The EOF is consistent from run to run because of the elimination of local pH differences and changes due to buffer depletion and other causes of EOF instability.
The EOF that is measured by the different High, Medium and Low flow capillaries is produced by the different amounts of sulfonic acid groups. The charge density is highly controlled but different between the 3 types of Controlled Flow Capillaries. This can be very helpful in cIEF.
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