The redox thermodynamics and kinetics of flavonoid rutin adsorbed at glassy carbon electrodes by stripping square wave voltammetry

Dried rutin nanocrystals have been prepared by lyophilization and investigated regarding their physicochemical properties with respect to re-dispersability, particle size, morphology and dissolution behavior. Photon correlation spectroscopy (PCS) and laser diffractometry (LD) were employed to determine the particle size. Morphology of the particles was analyzed by light microscopy. Lyophilized rutin nanocrystals were incorporated into tablets and the dissolution behavior of the tablets was evaluated. Very fine particles of lyophilized rutin could be completely re-dispersed in the water. The PCS size average and polydispersity index (PI) of lyophilized rutin were of 721nm and of 0.288 after re-dispersion. The rutin nanocrystal-loaded tablets were produced using direct compression. The dissolution velocity of the rutin nanocrystal-loaded tablet was superior compared to rutin microcrystal-loaded and a marketed tablet. After 30min rutin was released and dissolved completely from the nanocrystal tablets in water. In contrast, only 71% and 55% of the total amount of rutin were dissolved from the microcrystal tablets and the marketed tablet, respectively. The improving dissolution behavior of the rutin nanocrystal-loaded tablet should lead to a better bioavailability of the poorly soluble rutin in the body.

A rapid and sensitive assay for quantitative determination of rutin in oral dosage forms based on isocratic reversed phase high performance liquid chromatography (RP-HPLC) was developed and validated. Using a C(18) reverse-phase analytical column, the following conditions were chosen as optimal: mobile phase methanol-water 1:1 (v/v), pH 2.8 (adjusted with phosphoric acid), flow rate=1 mL min(-1) and temperature T=40.0 degrees C. Linearity was observed in the concentration range 8-120 microg mL(-1) with a correlation coefficient of 0.99982 and the limit of detection (LOD)=2.6 microg mL(-1), and limit of quantification (LOQ)=8.0 microg mL(-1). Intra- and inter-day precision were within acceptable limits. Robustness test indicated that the mobile phase composition and pH influence mainly the separation. The proposed method allowed direct determination of rutin in pharmaceutical dosage forms in the presence of excipients, but is not suitable for preparations where compounds structurally/chemically related to rutin may be present.