HORWITZ, Willeam ed. BF Method (Method II) : 26.021-26.025. Official Methods of Analysis of the Association of Official Analytical Chemists. 1970, 430-431
HORWITZ, Willeam ed. CB Method (Method I) : 26.015-26.020. Official Methods of Analysis of the Association of Official Analytical Chemists. 1970, 429-430