high % methanol and retention

[olivia]

Hi, can anyone tell me why at high % methanol peaks that were previously separated at low % methanol suddenly co-elute (c18 column). Or,can you point me in the right direction as to where I could read about this phenomenon.

Many thanks
Liv

[Jumpshooter]

your chromatography has changed b/c you have altered the composition of your mobile phase. By increasing the amount of MeOH relative to ACN, as you have done, you intentionally changed the polarity of your column thereby causing yor Tr to shift.

[AdrianF]

Hi
You would find it helpful to read a book about HPLC. The website below is the text of book on HPLC.
http://hplc.chem.shu.edu/HPLC/

Incidentally it would be helpful if a list of useful chromatography websites could be put together and posted on this site. Websites get mentioned from time to time but it is hard to remember which post they were in.

[tom jupille]

Incidentally it would be helpful if a list of useful chromatography websites could be put together and posted on this site. Websites get mentioned from time to time but it is hard to remember which post they were in.

It's in the "FAQ" section (link near the upper left of the screen) under the heading "where to obtain additional information".

[AdrianF]

Tom - thank you for the information about finding chromatographic websites etc . It looks very useful. Maybe you could find a way to publicise this more obviously.