An experimental investigation of the stability of ethylcellulose latex: correlation between zeta potential and sedimentation.
ABSTRACT This paper aims at explaining the experimental observations of the stability and redispersibility of an aqueous ethylcellulose latex through the electrokinetic characterization of the particles. The surface charge and the electrical double layer thickness play an essential role in the stability of the system, hence the need for a full characterization of the polymeric particles. The effect of both pH and ionic strength of the dispersion medium were investigated. It was found that at acid pH values the latex displays "delayed" or "hindered" sedimentation: in such conditions, the electrophoretic mobility and zeta potential are rather low, indicating a small electrokinetic charge on the particles. At alkaline pH, when the dissociation of ionizable surface groups must be complete, the zeta potential is high and negative. The electrostatic repulsion between polymer particles is responsible for the low sedimentation volume and poor redispersibility of the latex. The effect of NaCl and CaCl(2) concentration on both the zeta potential and stability of the latexes was also investigated: it was found that CaCl(2) has the greatest influence, yielding flocculated, easily re-dispersible systems when its concentration in the dispersion medium is high enough. There qualitative observations were ascertained by means of calculations of the potential energy of interaction between particles. In the case of NaCl solutions, a high and relatively wide potential energy barrier was predicted, that may prevent the particle aggregation. Above 5mM NaCl a shallow minimum in the potential energy curves must lead to the formation of aggregates. Similar results were found with CaCl(2) solutions, although in this case the secondary minima are deeper and appear at lower concentrations.
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ABSTRACT: In the present work comparative evaluation of acetate and pH gradient techniques for effective drug loading in liposomes has been investigated. The acetazolamide (ACZ) loaded liposomes prepared by two methods were analyzed by vesicle size analysis, zeta potential, percent encapsulation efficiency, in vitro drug release studies and intraocular pressure lowering activity. ICH guidelines were followed for determining stability of the prepared liposomes. The superiority of acetate gradient method for active loading of acetazolamide has been established. The prepared acetate gradient positive liposomes showed extended hypotensive effect when compared to other liposomal formulations. Thus ACZ loaded liposomes prepared by acetate gradient technique may serve as promising ocular delivery system in the treatment of glaucoma. The current work emphasizes the fact that the techniques used for active drug loading into liposomes strongly influence the pharmaceutical performance of the final formulation.International Journal of Pharmaceutics 11/2013; DOI:10.1016/j.ijpharm.2013.11.034 · 3.79 Impact Factor
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ABSTRACT: Bioavailability of a nanoparticulate formulation of coenzyme Q10 (NQ20), which has high stability in the water phase, was evaluated. The particle size was 188 nm, and the zeta potential value was between −38.8 and −44.8 mV at 4, 25, and 40°C in distilled water after eight weeks storage. Bioavailability of NQ20 was compared with a commercial coenzyme Q10 in oil and water phases as emulsified form using male Sprague-Dawley rats. After single oral administration of each coenzyme Q10 solution, the blood of rats was collected at 0, 1, 2, 3, 4, 5, 6, 9, and 12 h, and the concentrations of coenzyme Q10 were analyzed by high performance liquid chromatography. The plasma coenzyme Q10 levels at 1, 2, and 12 h were significantly higher when the rats were administered NQ20 compared to coenzyme Q10 in oil. The maximum plasma concentration (C max) and area under the concentration-time curve (AUC) values for NQ20 were 1.10±0.18 and 5.92±1.11 mM·h/mL, whereas the Cmax and AUC of coenzyme Q10 in oil were 0.79±0.07 and 5.30±0.62 mM·h/mL, respectively (p >0.05). Due to high absorbability and small particle size, NQ20 was found to have similar bioavailability to commercial coenzyme Q10 in the oil phase. Results indicate applicability of NQ20 in the food industry, particularly in beverages.Journal of the Korean Society for Applied Biological Chemistry 10/2012; 55(5). DOI:10.1007/s13765-012-2037-1 · 0.54 Impact Factor
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ABSTRACT: The electrokinetic potential of melamine-formaldehyde latex at high ionic strengths was measured by means of two different instruments. The present study confirms that the zeta potentials in 1 M 1-1 electrolyte solutions can be as high as +/-20 mV. The IEP of latex at low ionic strengths was at pH 11. The increase in the electrolyte concentration induced a shift in the IEP to low pH for all studied salts, and this indicates specific adsorption of the anions. The magnitude of the shift depends chiefly on the nature of the anion and increases in the series Cl < NO(3) = Br < I, and the nature of the cation (Li, Na, K, Cs) plays a rather insignificant role.Journal of Colloid and Interface Science 10/2006; 301(2):538-41. DOI:10.1016/j.jcis.2006.05.052 · 3.55 Impact Factor