The Cogent Diamond Hydride™ will be the best column to use for separation of these amino acids from among the Cogent TYPE-C™ silica hydride HPLC columns.

Aspartic acid and to some extent glutamic acid are sensitive to sodium in the system. Therefore, it is recommended to use the Teflon bottles for your mobile phase solvents instead of glass and to use RSA™ (reduced surface activity) glass autosampler vials (see link below). The second recommendation for optimal results is to add a small amount of TFA to the sample vial which can help peak shape. Glutamine is generally not a problem for retention or peak shape on the Cogent Diamond Hydride™.

A gradient is necessary to elute this group of compounds with a reasonable time frame and a preliminary method with starting points are described in the related articles listed below.

Cogent Diamond Hydride Product Page
RSA Glass Autosampler Vials