Browsing by Author "Borissova R."

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
  • No Thumbnail Available
    Item
    Relative effectiveness coefficient: A quality characteristic of toothpastes containing active components
    (1996-01-01) Borissova R.; Kirova E.
    It has been proposed that the parameter of relative effectiveness coefficient (REC) be used for the qualitative assessment of toothpastes containing active ingredients. REC is the ratio between the concentration of the active component in water eluates obtained after three minutes and adequately prolonged (up to the reaching of equilibrium state) dispersion of the toothpaste in distilled water at a 1:4 ratio (condition simulating the use of toothpaste in the oral cavity). The change in REC after storage following its production, as well as testing the toothpaste stability at high and low temperatures, provides an evidence for deviations in its quality. REC was applied for the assessment of toothpastes containing 0.5% zinc citrate as an active ingredient.
  • No Thumbnail Available
    Item
    Spectrophotometric study of competitive complexation equilibria involving overlapped spectral responding species: Determination of the stability constant of bismuth-pyrophosphate complex
    (2012-12-01) Nedeltcheva T.; Surleva A.; Nikolova L.; Borissova R.; Georgieva S.
    Spectrophotometric study of competitive complex formation equilibria involving overlapped spectral responding species applying a simple and versatile algorithm was carried out. The algorithm involves multivariable regression for calculation of equilibrium concentrations from multiwavelength data and mass action law for the stability constant calculation. The used regression functions are part of common statistical software. Stability constants and complex stoichiometry of competing equilibria were simultaneously determined. The species concentration profiles at several spectral overlapping and α-coefficient of competing reaction were obtained. Non-absorbing bismuth - pyrophosphate (PPh) system was studied as a competitive reaction of bismuth - 4-(2-Pyridylazo) resorcinol (PAR) complex. The formation of Bi-PPh complex with 1:1 stoichiometry was proved in the studied concentration region (C Bi = 1×10 -5 mol L -1; C PPh = 5×10 -6 - 1×10 -4 mol L -1). The stability constant of the complex at pH 1 and μ= 1.0 have been determined: logβ = 4.2±0.2. © Versita Sp. z o.o.