Determination of the viscosity and density of veterinary vaccines.

The quality of veterinary vaccines is monitored by physicochemical, microbiological and biological tests. Two of the most important physicochemical parameters are viscosity and density, which are determined in the three different types of matrices: emulsions, suspensions and solvents. Viscosity, known as internal friction or viscose medium, is a feature of fluids and plastic solids characterized by their internal resistance against flowing. Viscosity is one of the most important property of fluids (1). Newtonís law states that the force of the impact (friction) between layers of flowing liquid depends on their ratio, and the viscosity are directly proportional to the difference in flowing velocity of layers, and inversely proportional to the distance between them. Shear rate (Fig. 1) is the quotient of the velocity of liquid layers and the distance between them (2). According to the European Pharmacopoeia (3), there are two types of viscosity: dynamic and kinematic. The unit of dynamic viscosity (which is described in this paper) is the pascal ◊ second (Pa∑s). The most commonly used submultiple is the millipascal ◊ second (mPa∑s = cP). According to the European Pharmacopoeia (4), the relative density of a substance is the ratio of the mass of a certain volume of a substance at temperaDETERMINATION OF THE VISCOSITY AND DENSITY OF VETERINARY VACCINES