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In the production of chemical substances, especially pharmaceuticals, it is important to ensure that the products are pure and uncontaminated. If we want a particular reaction to occur we need to be sure that only the required reactants are present, otherwise unforeseen products may be formed and may change the properties of the substance we are trying to make. The un-purified raw materials are processed to the required purity so that they can be used as feedstock in a variety of pharmaceutical processes.
In almost all chemical reactions there will be more than one substance formed. The substance we want to produce is called the product and any other substances formed are called co-products or by-products. These co-products and any unreacted substances must be removed before the product can be used for commercial purposes, for both safety and quality reasons. The degree of purity required varies depending on the use. If the substance is used in food or in medicines, then purity is of the highest importance.
There are numerous ways to purify substances and the methods used depend on the physical and chemical properties of the substances involved. In most cases more than one method is needed to achieve the desired product purity. When a substance is separated, purified and collected for use, it is said to be harvested.
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