This suggests that the bonded phase of the UDC-Cholesterol™ column provided the separation mechanism for Glyburide but not Metformin under these conditions.

HOW DOES THIS WORK WITH METFORMIN? Page 20 cont.
The Aqueous Normal Phase Separations of Metformin at approximately 50% acetonitrile results in a longer retention time as the acetonitrile percentage increases. This occurs at the same percentage for both the un- bonded and bonded phases.

This suggests that the silica surface of both columns provides the main separation mechanism for Metformin regardless of the bonded phase.

HOW DOES THIS WORK WITH GLYBURIDE? Page 21
The Aqueous Reverse Phase separation of Glyburide on the Un-bonded TYPE-C Silica™ column shows retention at 27% acetonitrile, but no retention at 35%. With the bonded UDC-Cholesterol™ column, even at 80% acetonitrile, the Glyburide is retained.

The bonded Cogent UDC-Cholesterol™ column, under the same conditions, separates Glyburide much differently fron that of the un-bonded TYPE-C Silica™ column.

This suggests that the bonded phase of the UDC-Cholesterol™ column provided the separation mechanism for Glyburide but not Metformin under these conditions.

COGENT UDC-CHOLESTEROL™ SEPARATION FOR GLYBURIDE? Page 22
It can be seen that the silica hydride has no reverse phase reteention above 35% acetonitrile.

The reverse phase retention on the Cogent UDC-Cholesterol™ column above 50% acetonitrile must, therefore, be totally a function of the bonded phase.

This suggests that the retention characteristics of the bonded phase must be taken into account when considering the retention by reverse phase,as well as, the compount itself.

KEY DIFFERENCES OF TYPE-C™ PHASES Page 23
A key difference to understanding the uniqueness of TYPE-C™phases is that it is possible to have different compounds (Metformin and Glyburide) use different separation mechanisms (ANP & ARP) in the same analysis on the same column.

Within the mechanisms above, the choice of un-bonded TYPE-C Silica™, bonded Cogent UDC-Cholesterol™ or bonded Cogent Bidentate C18™, can each produce a reverse phase response; which can be due to the silica hydride surface or the bonded phase as dominant factors in the separation or combinations of the two.