Resonance Rayleigh Scattering Spectrometric Determination of Amoxicillin by Its Reaction with Methylene Blue

In a Tris-HCl buffer medium of pH 8.93, an appropriate amount of amoxicillin sample solution was reacted with 1.5 mL of 1.0×10-5mol·L-1 methylene blue solution in a total volume of 10 mL, to form an ion association complex, of which the intensity of resonance Rayleigh scattering (IRRS) was measured at the wavelength of 369 nm. Values of ΔIRRS (difference between values of IRRS of sample and blank) were found to keep linear relationship with values of concentration of amoxicillin in the range of 2.0×10-7-1.0×10-6mol·L-1, with detection limit (3s/k) of 7.8×10-8mol·L-1. The proposed method was applied to the determination of amoxicillin in samples of capsules and injections, results obtained by this method were found to check quite well with the results found by the method of pharmacopeia.