High-performance liquid chromatographic determination of peptides in biological fluids by automated pre-column fluorescence derivatization with fluorescamine

Peptides containing a free alpha- or epsilon-amino group react with fluorescamine under mild alkaline conditions to generate a highly fluorescent but unstable reaction product and, consequently, practical high-performance liquid chromatographic (HPLC) approaches to analysis have typically involved the use of postcolumn derivatization. An automated precolumn approach is reported in which peptides are reacted with fluorescamine just prior to HPLC analysis by a commercially available autoinjector with derivatization capabilities. The autoinjector added base and fluorescamine reagent solutions to a sample vial containing peptide analytes, and the derivatization reaction was allowed to proceed for 5 min at room temperature prior to injection into the HPLC system. The derivatized peptides were analyzed by reversed-phase HPLC with fluorescence detection (excitation at 390 nm; emission 470-nm cut-off filter) on an octylsilica column. Optimization of the precolumn reaction conditions and the use of narrower HPLC columns (2 mm I.D.) resulted in a typical on-column detection limit of 30-50 fmol of peptide, which was substantially lower than that in previously reported post-column methods. This approach was applied to the HPLC of several naturally occurring and synthetic peptides containing alpha- and epsilon-amino groups. In combination with solid-phase extraction, prior to automated precolumn fluorescence derivatization and chromatographic analysis, the methodology was used for the determination of a synthetic growth hormone-releasing peptide in plasma samples.