Objective: To substantiate the possibility of using polarimetry to control the quality of tinctures as an additional pharmacopoeial method.
Methods: The polarimetric method (POL-1/2, Atago, Japan, the measurement accuracy of±0.002 °) was used to measure the optical activity (α °) of motherwort, valerian and hawthorn tinctures. The dynamic light scattering method (DLS; Zetasizer Nano ZS, Malvern, UK) was used to assess the stability of alcoholic and aqueous dilutions of tinctures according to the intensity of dynamic light scattering dependent on the size (d, nm) of the dispersed phase particles and the values of the electrokinetic potential (ξ, mV).
Results: For the first time in this investigation, the polarimetry approach was proposed to evaluate the cardiotonic and hypotensive tinctures' quality and for their identification. Valerian tincture, dilution 1:40,-0.10°<α°<-0.89°; motherwort, tincture-dilution 1:10,-0.10°<α°<-2.21°; hawthorn, tincture without dilution,-0.76°<α°<-1.55°-these are the acceptable ranges of optical activity (α°) of their alcohol dilutions. Beyond these intervals, the use of the polarimetric approach is impossible. Values of optical activity below 0.1 correspond to too low a content of optically active components. Tinctures with optical activity above the upper value of the interval were unstable dispersed systems with low values of the electrokinetic potential (|ξ|≪25mV) and micron particle sizes. Reference tinctures were made from raw materials (Leonurus cardiaca L.) to verify the results. The quality parameters: optical activity (α°), spectra of dynamic light scattering by intensity, volume, and number ("I-d"; "V-d"; "N-d"), electrokinetic potential (ξ) values, and photon pulse count per second (Count Rate, kcps) corresponded to the results obtained for pharmaceutical dosage forms.
Conclusion: The permissible intervals of optical activity (α°) of their ethanol dilutions, as well as their relationships with the particle size of the dispersed phase and the values of the electrokinetic potential, were established for the first time to evaluate the quality of tinctures. The obtained results show that polarimetry can be recommended as an additional pharmacopoeial quality control method for tinctures
