Chromatography Forum

good morning
i ve been working with seven principal compunds of ginseng extract.
Two of them, i can't separate.

I use a c18 column...m.ph is acetonitrile :water with a gradient
my question is...if i can't resolve the first two peakes changing the composition of gradient ,what can i do....change the column ?
The method is from USP 30.
Some of my collegues say to me that i would change the reference of column,i.e.choose other c18 .
in the other hand,the cuantification is by summary of areas of the six principal peaks...I know the RT of them,only that,resolve two of them is very difficult...Can I do the summary of them whitout the better resolution.
Many thanks to all for your comments
Pduque

Rg and Re pretty much need to be separated using an isocratic hold followed by gradient elution of the rest on C18. This is a very classical approach and the literature is full of examples. I have had some luck with a phenyl column and a very shallow gradient of those first two, but there is little advantage to this as you still end up with multiple gradient steps.

You need to check, what specific column has been qualified for this assay. Once you have this information, you should be able to reproduce the method without difficulty.