Can any body explain the analytical HPLC methods for the separation of the diastereo isomers?
Thank you.

Diastereomers have at least two chiral atoms. so you can get RR, RS, SR, SS diastereomers. With usual RP chromatography you will not be able to separate RR and SS (assuming that there are no further chiral atoms) and SR and RS from each other. You might be able to separate RR (or/and SS) from RS (and/or SR).
Imagine the shape of the molecule: separation is possible if distances between two not directly connected atoms are different. Then, the peak shape is different and you might get chromatographic separation.

Chiral chromatography can be accomplished in many ways. What molecule are you working on and what is/are the chiral carbons like?

Separation of diastereomers can be based on
differences in physical properties or spatial
orientation (ability to form inclusion complexes).
In the former case you are looking at reversed
phase chromatography, in the latter perhaps a
cyclodextrin column. Are you dealing with
optically active or geometric (e.g.
cis/trans) diastereomers?

If my memory doesn´t fail me then the term diastereomer is used for optical isomers which are not mirror images of each other (are not optical antipodes, that is, do not rotate polarized light equally in opposite directions). These separate with mechanisms like any other compounds, no chiral stationary phases, etc., are needed. Or: Their physical and chemical interaction with nonchiral materials is different.

The definition I am using states that any
stereoisomers that are not enantiomers are
diastereomers. This means that all geometrical
isomers are diastereomers.

An early separation of diastereomers based on
spatial orientation was described by Armstrong et
al in " Liquid Chromatographic Separation of
Diastereomers and Structural Isomers on
Cyclodextrin-Bonded Phases" (Anal Chem. 57
234-237,

Checked my old refs, Buglio is right on the definition of diastereomers (Mislow, Introduction to Stereochemistry: "Stereoisomers which are related as object and nonsuperimposable mirror image are called enantiomers or antipodes, whereas those which are not so related are called diastereomers". He then proceeds to make clear that "diastereomer" does not apply only to optical [chiral] isomers.)
To get back to the original question, another quote from Mislow should give the answer:
"In short, diastereomers, like constitutional isomers, differ in every single physical property and are conspicuously different chemical entities." Thus, one can approach their separation as for all other "conspicuously different chemical entitities".

Does anyone know what can be the cause of the base line ramp that I’m having when I try a gradient run of acetonitrile(ACN)/water 40:60 to 100:0 ? The column that I use is a C18 4.6mm X 15cm, dp 5um.
The baseline ramp seems to follow the increase in concentration of the ACN. I don’t want to believe that it’s impurity because I filter the solvents and the ramp doesn’t show when the run is isocratic no matter the solvents proportion that I use (40:60, 50:50, … )

Thank you.

Can any body explain the analytical MASS SPECTROMETRY methods for the separation of the diastereo isomers?
Thank you.

diasteriomers diffrentiation and quantification aslo done by mass spectrometry
glucosamine, galuctosamine and mannosamine were diffrentiated by proton affinity order and quantification also done in recent anal chem paper
thank you