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 Metformin & Glyburide, A Real Life Application A 3 minute isocratic analysis on TYPE-C™ HPLC Columns It is always more useful to chromatographers to read about a real life separation challenge and how it was solved. Theoretical situations are very helpful to understand the character of phases but real life case studies are more practical. Here is a real life situation and how the separation challenge was met and optimized. The pharmaceutical formulation of the highly polar molecule, Metformin (LogP of minus 2.64) and the relatively non polar molecule Glyburide (LogP 4.79) are of interest to many Generic Pharmaceutical companies that are considering its analysis. Ideally a simple quick isocratic analysis was desired. But Metformin is so polar that when examined, its retention on all of the following Type-B HPLC columns was unsatisfactory: HPS™ C18, hQ™ C8, Axis™ C18, Axis™ Phenyl, Cogent F5™, HPS™ Cyano or HPS™ Amino using Cogent Mini-Scout™ Strategy were all used. It should be noted that metformin was too polar to be retained on C8, C18, cyano or amino columns. Metformin was not retained in 100% aqueous, or buffered a queous. This was a problem. Then 2 different TYPE-C™ phases were examined. Both TYPE-C Silica™ and Cogent UDC-Cholesterol™ columns gave a good symmetrical peak shape for Glyburide, but a slightly tailing peak for Metformin standards when run independantly. However, Glyburide was a broad but symmetric peak on a TYPE-C Silica™ column, but a relatively narrow symmetric peak could be achieved if the acetonitrile concentration was adjusted so as to give the same retention time that it had on a Cogent UDC-Cholesterol™ column with the same column dimensions. Either TYPE-C Silica™ or TYPE-C™ based UDC-Cholesterol™ columns can be utilized when separating these two compounds, but the latter was the preferred column because of the better peak width and relative selectivity after trying both of them.  Click here to see actual chromatogram of Metformin and GlyburideSeparated by the above. How did we separate both compounds in one isocratic run? 
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