The American Chemical Society (ACS) Committee on Analytical Reagents sets the specifications for most chemicals used in analytical testing. Currently, the ACS is the only organization in the world that sets requirements and develops validated methods for determining the purity of reagent chemicals. These specifications have also become the de facto standards for chemicals used in many high-purity applications. Publications and organizations that set specifications or promulgate analytical testing methods-such as the United States Pharmacopeia and the U.S. Environmental Protection Agency-specify that ACS reagent-grade purity be used in their test procedures. The Eleventh Edition incorporates the "supplements" accumulated over the past eight years, removes some obsolete test methods, improves instructions for many existing ones, and also introduces some new methods. Overall, the safety, accuracy, or ease of use in specifications for about 70 of the 430 listed reagents has been improved, and seven new reagents have been added.