for my degree work

[pamelaquimica]

good afternoon, as I told you I'm trying to develop an HPLC method validation for amino acids, I can not separate the histidine from serine and aspartic acid from glutamic acid, the gradient have changed many times and I've failed, what else I can do, thanks.

[yangz00g]

Try different columns. There are quite few manufactures make column specific for AA, like Tosh(?). If you use heavy matrices, separating all of them is a tough task.

[Vlad Orlovsky]

Try ion-pairing reagent with any C18 column, or alternatively try mixed-mode Primesep HPLC column:
http://www.sielc.com/compound_002.html

Contact me if you have questions.