Micellar enhanced fluorimetric determination of 1-NN-dimethylaminonaphthalene-5-sulphonyl chloride and o-phthalaldehyde-2-mercaptoethanol derivatives of amino acids

Abstract

The effects of various surfactant micellar systems upon the spectrofluorimetric method for the determination of amino acids by Roth's method and the dansyl chloride procedure have been assessed. Specifically, the fluorescence intensity of dansyl glycine was found to be remarkably enhanced when in the presence of cationic hexadecyltrimethylammonium chloride or dodecyltrimethylammonium chloride and zwitterionic N-dodecyl-NN-dimethylammonium-3-propane-1-sulphonic acid micellar systems. Likewise, the lysine derivative of o-phthaladehyde-2-mercaptoethanol exhibited intensified fluorescence when in the presence of non-ionic Brij-35 or Triton X-100 and anionic sodium dodecylsulphate micelles. Depending upon the type of surfactant micellar system employed, fluorescence enhancements of from 8 to 20 were observed in comparison with that in water alone. Owing to this micellar phenomenon, the sensitivity of the fluorimetric methods for the determination of these two species was correspondingly increased from 8- to 20-fold over the conventional procedures. The spectral parameters, quantum yields, lower detection limits and analytical figures of merit for these two substances in the micellar systems and water alone are compared. Possible reasons for this observed micellar induced enhanced fluorescence are given. A brief prospective on the general applicability of using micelles to enhance other fluorimetric methods is also given.