1. Joint Committee of the American Academy of Forensic Sciences (AAFS) and the Society of Forensic Toxicologists, Inc. (SOFT), Forensic Toxicology Laboratory Guidelines, Colorado Springs, 2002. Available online from www.soft-tox.org.
2. Schenk, G.H., Hahn, R.B., and Hartkopf, A.V. Fundamentals of weighing and related measurements, in Quantitative Analytical Chemistry - Principles and Life Science Applications, Allyn & Bacon, Boston, 1977, chap.6.
3. Blanke, R.V., Validation of the purity of standards, Publication 87-0175, Abbott Laboratories, Diagnostics Division, Irving, TX, 1989.