What are "primary amino acids and secondary amino acids"? Context: analysis of amino acid content using reversed-phase HPLC
I would guess that 'secondary' refers to amino acids that have been derivatized in some way, possibly by reacting with o-phthalaldehyde. (To measure the fluorescence of an OPA-derivatized amino acid, you excite at 340 nm, so I presume the derivative will absorb at this wavelength?).