Frequency doubling scattering and second-order scattering technology as novel methods for the determination of the inclusion constant of procaine hydrochloride to β-cyclodextrin Original Research Article

The frequency doubling scattering (FDS) and second-order scattering (SOS) intensities of procaine hydrochloride solution were weak. When β-cyclodextrin was added to the procaine hydrochloride solution, it can form a 1:1 inclusion complex with procaine hydrochloride established by spectrophotometry, and the FDS and SOS intensities were enhanced greatly. Their maximum scattering wavelengths appeared at 390 nm for FDS and 480 nm for SOS, respectively. The intensities of FDS and SOS at their maximum scattering wavelengths increased with an increase in β-cyclodextrin concentration. Based on this fact, the FDS and SOS methods were first applied to the determination of the inclusion constant of procaine hydrochloride to β-cyclodextrin. The inclusion constant, Kf, of the procaine hydrochloride–β-cyclodextrin complex were 1.11×102−1.19×102 l mol−1 for the FDS and SOS methods. To compare with these methods, the spectrophotometric and fluorescence experiments have been done with satisfactory results.