Reference Substances and Infrared Reference Spectra for Pharmacopoeial Analysis (WHO Technical Report Series, No. 885, 1999: Annex 3): 2. General guidelines for the establishment, maintenance and distribution of chemical reference substances - Reprint from WHO Technical Report Series, No. 885, 1999: Annex 3: Part A. Primary chemical reference substances: 3. Evaluation of chemical reference substances: 3.2 Use in purity tests

Reference Substances and Infrared Reference Spectra for Pharmacopoeial Analysis (WHO Technical Report Series, No. 885, 1999: Annex 3)
(1999; 117 pages)

Table of Contents

Preface¹
1. Compilation of national, regional and international reference substances and infrared reference spectra
	1.1 Reference substances for pharmacopoeial analysis
		Addresses for the purchase or the source of reference substances
		List of reference substances
	1.2 Infrared reference spectra for pharmacopoeial
		Addresses for the purchase or the source of reference spectra
		List of infrared reference spectra
2. General guidelines for the establishment, maintenance and distribution of chemical reference substances - Reprint from WHO Technical Report Series, No. 885, 1999: Annex 3
	Introduction
	Part A. Primary chemical reference substances
		1. Assessment of need for the establishment of chemical reference substances
		2. Obtaining source material
		3. Evaluation of chemical reference substances
			3.1 Use in identification tests
			3.2 Use in purity tests
			3.3 Use in assays
			3.4 Use in the calibration of an instrument
		4. Chemical and physical methods used in evaluating chemical reference substances
			4.1 Methods used to verify the identity of chemical reference substances
			4.2 Methods used to determine the purity of chemical reference substances
				4.2.1 Separation techniques
				4.2.2 Methods based on intrinsic thermodynamic properties
				4.2.3 Other methods
		5. Assignment of content
		6. Handling and distribution of chemical reference substances
			6.1 Packaging operations
			6.2 Storage
			6.3 Stability
			6.4 Information to be supplied with chemical reference substances
			6.5 Distribution and supply
			6.6 Period of use
	Part B. Secondary chemical reference substances
	References
Back cover

3.2 Use in purity tests

The characterization of a chemical reference substance used in the determination of a specific impurity is more extensive, especially when used in a limit test. If the technique employed is thin-layer chromatography (TLC) an acceptable minimum purity is recommended (normally at least 90%), but purer material may be required for liquid chromatography (LC) or gas chromatography (GC). If the proposed reference substance is being prepared or isolated for the first time, appropriate chemical and physicochemical tests, such as nuclear magnetic resonance (NMR), mass spectrometry (MS) and elemental analysis, must be applied to characterize it.