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Objectives of mixing in Pharmacy
The aim of mixing is to ensure that there is uniformity of composition between the mixed ingredients that represent the overall composition of the mixture. The primary objective of mixing is to make a homogeneous product using the minimum amount of energy and time.
The other objectives are as follows:
(i) To produce a single physical mixture
This may be simply the production of a blend of two or more miscible liquids or two or more uniformly divided solids. In pharmaceutical practice, the degree of mixing must commonly be of a high order as many of such mixtures are dilutions of active substances and must be in accurate amount for dose uniformity in dosage forms.
(ii) To produce physical change
Mixing can be performed to produce physical as well as chemical change, for example, solution of a soluble substance. In such cases, a the lower efficiency of mixing is often acceptable because mixing merely accelerates a dissolution and diffusion process that could occur by simply agitation.
(iii) To produce dispersion:
Mixing is also aimed to include the dispersion of two immiscible liquids to form an emulsion or dispersion of a solid in liquid to give a suspension or paste. Usually, good mixing is required to ensure stability and
(iv) To promote chemical reaction
Mixing encourages and at the same time control a chemical reaction. Mixing ensures a uniform product such as reactions where accurate adjustment to pH is required and the degree of mixing will decide the possibility of reaction.
Mixing fulfills many objectives beyond a simple combination of raw ingredients. These include preparing fine emulsions, reducing particle size, carrying out chemical reactions, manipulating rheology, dissolving components, facilitating heat transfer, etc. So even within a single pharmaceutical product line, it is a common practice to employ a number of different style mixers to process raw ingredients, handle intermediates and prepare the finished product.