https://www.pharmacyword.com/post/sources-of-impurities-of-drugs

The quality of all substances used as medicines or in the preparation and processing of pharmaceutical products must be of highest standard so that the medicine will not cause any harm to the patients due to the presence of impurities. Therefore, testing of purity of the medicines becomes very important.

Quality Control (QC) and Quality Assurance (QA):

Quality Control is usually the complete test protocol for any substance. Quality Assurance is a much broader concept. Quality Assurance includes analysis of premises, process, products, equipment, people, labeling, packaging and storage. Both Quality Control and Quality Assurance form a core of new pharmaceutical industry and services.

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https://www.pharmacyword.com/post/sources-of-impurities-of-drugs