Cyclodextrin enhanced fluorimetric method for the determination of tryptamine

The effect of native cyclodextrins (alpha-, beta- or gamma- with six; seven or eight glucose units, respectively), hydroxypropyl-beta-cyclodextrin, beta-cyclodextrin solubilized in urea, soluble starch and glucose in water solution on the fluorescence behaviour of tryptamine [3-(2-aminoethyl)indole] (T) was determined. In addition, the effect of methanol and propanol with and without beta-cyclodextrin Or hydroxypropyl-beta-cyclodextrin was ascertained. From the fluorescence changes with pH and with beta-cyclodextrin or hydroxypropyl-beta-cyclodextrin, the values of the pK(a), of the ground and excited states and the association constants of T and TH [3-(2-ammoniumethyl)indole] with the two hosts were determined. The values are pK(a), = 9.5 +/- 0.2 and pK(a)* = 8.4 +/- 0.2; K-Assoc(TH) = (1.6 +/- 0.3) x 10(2) mol(-1) dm(3) and K-Assoc(T) = (2.8 +/- 0.3) x 10(2) mol(-1) dm(3) with beta-cyclodextrin, K-Assoc(TH) = (1.8 +/- 0.5) x 10(2) mol(-1) dm(3) and K-Assoc(T) = (4.9 +/- 0.9) x 10(2) mol(-1) dm(3) with hydroxypropyl-beta-cyclodextrin. The ratio of the fluorescence quantum yields for the bound and fi ee substrate (Phi(b)/Phi(f)) were in the range 1.25-1.33, The detection limit for the better conditions where the host-guest interactions produce fluorescence enhancement was 0.454 +/- 0.002 ng ml(-1) for the complex T-hydroxypropyl-beta-cyclodextrin in water. The method is simpler than others reported previously.