Sensitive liquid chromatograhic determination of hydrophobic primary and secondary amines by derivatization to form highly fluorescent thiazoles

Thioureas formed by addition of primary and secondary amines to the non-fluorescent 5-isothiocyanato-l,3-dioxo-2-p-tolyl-2,3-dihydro-1H-benz[de]isoquinoline were oxidized to the corresponding stable and highly fluorescent thiazoles with large Stokeʹs shifts. The structure of the thiazoles was deduced. Liquid Chromatographic separation of the thiazoles in both normal phase (NP) and reversed phase (RP) systems was achieved. Fluorescence detection limits ranged from 2 to 8 f mol in the RP and NP systems. The fluorescence properties (maximal wavelengths and intensities) of the thiazoles are dependent on the solvent. An application to the determination of 2-phenylethylamine in cocoa powder is given.