It depends. Some isomers will react differently with HPLC column, and therefore will have different retention times. For example, a branched chain isomer will typically have less interaction with the packing of the column, and will elute early, while a straight chain isomer will tend to have more interaction with the column and will elute later. In cases like this, you will see multiple peaks in a chromatogram, which each represent a different isomer. However, this is very dependent on the type of isomer (for example stereoisomers, or large molecules with isomers that are very similar in structure will be difficult to separate) and also dependent on the relationship between the compound and the column, and the mechanism of interaction between the two. I hope this is helpful.

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