ginseng asian extract

[paul duque]

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

[AA]

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.

[Uwe Neue]

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.