A non-fluorescent reagent that reacts readily under mild conditions with primary amino groups in amino acids and peptides to form stable and highly fluorescent derivatives. Low background due to hydrolysis. Useful in fluorometric assays of amino acids, protein, and proteolytic enzymes. Effectively blocks newly generated amino termini in protein sequence analysis by the Beckman automated sequencer. Spectral data: Exc. 390nm/Em. 475 nm in 0.5 M borate buffer, pH 8.5, after derivatization with L-leucine.