EXTRACTION-PHOTOMETRIC DETERMINATION OF TORASEMIDE

Abstract

The method of extraction-photometric research and computer modeling has proven the possibility of forming an ion pair of torasemide (Tor) with the cationic reagent astrafloxin FF (AF) forming an ion pair (IP). The energy efficiency of IP formation and its dipole moment have been calculated and shown. Calculations in the Tor- + AF+ system were performed using the HyperChem 8.0 package. Various initial variants of the counterions’ arrangement relative to each other (the “single point” procedure) were used. Geometric optimization of the ions was performed by the molecular mechanics method MM+. The studied IPs are quite well extracted by various aromatic hydrocarbons and can serve as an effective analytical form for the extraction-photometric determination of torasemide. The optimal conditions for the formation and extraction of IP were established: maximum extraction by an organic solvent from the aqueous phase is observed at pH 5–9; the optimal reagent content in the aqueous phase is in the range (1.5–3.0) 10-4 M. The optimal extraction time is 50–60 s. The composition of IP was established by classical spectrophotometric methods: equilibrium shift and isomolar series. It is shown that IP with a component ratio of 1:1 is well extracted into the organic phase. The conditional molar light absorption coefficient of IP under optimal conditions reaches 1.0 ⋅ 105. The calibration graph of the dependence of the optical density of extracts on the Tor concentration is described by the equation of the straight line A = 0.011 + 0.052 c(Tor) in the concentration range of 0.8–46.8 μg/cm3 Tor. The detection limit of Tor, calculated by the 3 s criterion (n = 5; P = 0.95), is 0.7 μg/cm3. A method for extraction-photometric determination of torasemide in dosage forms and biofluids of athletes has been developed.