Quality Assurance of Pharmaceuticals - A Compendium of Guidelines and Related Materials - Volume 1
(1997; 248 pages) [French] View the PDF document
Table of Contents
Open this folder and view contentsIntroduction
Open this folder and view contents1. National drug regulation
Open this folder and view contents2. Product assessment and registration
Open this folder and view contents3. Distribution
Close this folder4. The international pharmacopoeia and related activities
View the documentGuidance for those preparing or commenting on monographs for preparations to be included in The international pharmacopoeia1
View the documentValidation of analytical procedures used in the examination of pharmaceutical materials1
Close this folderGeneral guidelines for the establishment, maintenance, and distribution of chemical reference substances1
View the document1. Criteria for determining the need for the establishment of chemical reference substances
View the document2. Evaluation of reference substances
Close this folder3. Chemical and physical methods used in evaluating reference substances
View the document3.1 Methods useful for verifying the identity of reference substances
View the document3.2 Purity requirements for reference substances
View the document3.3 Methods used in determining the purity of reference substances
Open this folder and view contents4. Handling and distribution of reference substances
View the document5. Reference materials calibrated against International Chemical Reference Substances
View the document6. Means of promoting effective exchange of information and ensuring cooperation between organizations establishing reference substances
View the documentGeneral recommendations for the preparation and use of infrared spectra in pharmaceutical analysis1
View the documentList of available International Chemical Reference Substances1
View the documentList of available International Infrared Reference Spectra1
Open this folder and view contents5. Basic tests
Open this folder and view contents6. Laboratory services
Open this folder and view contents7. International trade in pharmaceuticals
Open this folder and view contents8. Counterfeit products
Open this folder and view contents9. Training
View the documentSelected WHO publications of related interest
View the documentBack cover
3.2 Purity requirements for reference substances

The purity requirements for a reference substance depend upon its intended use. A reference substance proposed for an identification test by infrared spectrophotometry does not require meticulous purification, because the presence of a small percentage of impurities in the substance often has no noticeable influence on its infrared spectrum. Similarly, reference substances that are applied in low loadings in thin-layer chromatographic tests need not be highly purified.

On the other hand, reference substances that are to be used in assays should preferably possess a high degree of purity. As a guiding principle, a purity of 99.5% or better is desirable for such reference substances, although in cases where the precision of the analytical procedure for which the reference substance is required is low, such a degree of purity may not be necessary. In making a decision about the suitability of a reference substance, the most important consideration is the influence of the impurity on the attribute measured in the assay. Impurities with physicochemical characteristics similar to those of the main component will not impair the usefulness of a reference substance, whereas even traces of impurities with significantly different properties may render a substance unsuitable as a reference substance.

to previous section
to next section
The WHO Essential Medicines and Health Products Information Portal was designed and is maintained by Human Info NGO. Last updated: December 6, 2017