WHO Expert Committee on Specifications for Pharmaceutical Preparations - WHO Technical Report Series, No. 885 - Thirty-fifth Report
(1999; 168 pages) [Spanish] View the PDF document
Table of Contents
View the documentWHO Expert Committee on Specifications for Pharmaceutical Preparations
View the document1. Introduction
Open this folder and view contents2. The international pharmacopoeia and related issues
Open this folder and view contents3. International Chemical Reference Substances and Infrared Reference Spectra
Open this folder and view contents4. Quality control - national laboratories
Open this folder and view contents5. Good manufacturing practices
Open this folder and view contents6. Quality systems and inspection
Open this folder and view contents7. Other quality assurance topics
Open this folder and view contents8. Nomenclature and terminology
Open this folder and view contents9. Legal aspects of pharmaceuticals
Open this folder and view contents10. Regulatory issues
Open this folder and view contents11. Training activities
View the document12. Pharmaceuticals contaminated with diethylene glycol
View the documentAcknowledgements
View the documentReferences
View the documentAnnex 1. List of available International Chemical Reference Substances1
View the documentAnnex 2. List of available International Infrared Reference Spectra1
Close this folderAnnex 3. General guidelines for the establishment, maintenance and distribution of chemical reference substances
View the documentIntroduction
Close this folderPart A. Primary chemical reference substances
View the document1. Assessment of need for the establishment of chemical reference substances
View the document2. Obtaining source material
Close this folder3. Evaluation of chemical reference substances
View the document3.1 Use in identification tests
View the document3.2 Use in purity tests
View the document3.3 Use in assays
View the document3.4 Use in the calibration of an instrument
Open this folder and view contents4. Chemical and physical methods used in evaluating chemical reference substances
View the document5. Assignment of content
Open this folder and view contents6. Handling and distribution of chemical reference substances
View the documentPart B. Secondary chemical reference substances
View the documentReferences
Open this folder and view contentsAnnex 4. Good manufacturing practices: authorized person - role, functions and training
Open this folder and view contentsAnnex 5. Good manufacturing practices: supplementary guidelines for the manufacture of pharmaceutical excipients
Open this folder and view contentsAnnex 6. Guidelines for inspection of drug distribution channels
View the documentAnnex 7. Good pharmacy practice in community and hospital pharmacy settings
Open this folder and view contentsAnnex 8. National drug regulatory legislation: guiding principles for small drug regulatory authorities
Open this folder and view contentsAnnex 9. Provisional guidelines for developing training programmes: inspection and examination of counterfeit pharmaceuticals
View the documentWorld Health Organization Technical Report Series
View the documentSelected WHO Publications of Related Interest
View the documentBack Cover
 
3.3 Use in assays

If the chemical reference substance is to be used in an assay (colorimetry, LC, GC or UV spectrophotometry), the extent of testing is very much greater. Several (a minimum of three) laboratories should collaborate in testing the proposed substance, using a variety of established and validated techniques, including the method used in the pharmacopoeial specification. The relative reactivity or relative absorbance of the impurities present must be checked when a nonspecific assay method is employed, e.g. by colorimetry or UV spectrophotometry. When a selective assay method is employed, it is particularly important to determine the quantity of impurities. In such a case, it is best to examine the proposed reference substance by as many methods as practicable including, where possible, absolute methods. For substances that are acidic or basic a titration with alkali or acid is simple, but other reactions which are known to be stoichiometric may be used. Phase solubility analysis and differential scanning calorimetry may also be employed in certain cases.

The total of the determinations of water content, organic solvents, mineral impurities and organic components should amount to 100%. For most chemical reference substances intended for assays, the content may be expressed "as is". When establishing the chemical reference substance it is therefore essential to determine the content of water and residual solvents for a non-specific assay, and also to determine the content of impurities for a selective assay.

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