INDIVIDUAL AND JOINT STOPPED-FLOW KINETIC SPECTROFLUOROMETRIC DETERMINATION OF NEOMYCIN AND TYROTHRICIN

Kinetic methodology was used for the first time to develop a simple, f ast spectrofluorimetric method for the determination of neomycin and t yrothricin using the stopped-flow mixing technique. The proposed metho d involves reaction of these antimicrobial substances with o-phthaldia ldehyde in the presence of N-acetylcysteine, which is used as a thiol reagent. Neomycin and tyrothricin can thus be determined simultaneousl y by applying the proportional-equation method to the initial rate and signal increment of the kinetic curves obtained for each analyte. The reaction rate can be determined in ca. 1 s and the signal increment i n ca. 3 s. The calibration graph was linear over the range 0.07-70 mu g ml(-1) neomycin and 0.08-40 mu g ml(-1) tyrothricin. The mid-range r elative standard deviation was less than 3%. The proposed method was a pplied to the individual determination of these compounds in pharmaceu tical samples, with a recovery of 98.1-103.6% for neomycin and 92.0-10 8.0% for tyrothricin. Synthetic mixtures of neomycin and tyrothricin i n ratios between 1:4 and 4:1 were also satisfactorily analysed.