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2. Precision of Test Methods, Geneva, 1994, ISO 5725 (previous editions were issued in 1981 and 1986).
3. M. Thompson, R. Wood (Editors), The International Harmonised Protocol for the Proficiency Testing of (Chemical) Analytical Laboratories, Pure Appl. Chem. 65 (1993) 2123 (also published in J. AOAC Int. 76 (1993) 926).
4. M. Thompson, R. Wood (Editors), Guidelines on internal quality control in analytical chemistry laboratories, Pure Appl. Chem. 67 (1995) 649.
5. Report of the 21st Session of the Codex Committee on Methods of Analysis and Sampling, FAO, Rome, 1997, ALINORM 97/23A.