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Pharmaceutical Standards for Drinking Water Analysis

Authors: Derrell Johnson, Uma Sreenivasan PhD, Kevin Gates, Ning Chang PhD, Isil Dilek PhD, Huahua Jian PhD, Mitzi Rettinger
Presented at NMEC, August 2009

Abstract
Contamination of drinking water supplies with pharmaceuticals is of increasing concern around the U.S. Trace levels present a potential threat to health and the environment. Identification and quantitation of pharmaceutical impurities is effluent and drinking water is an emerging focus for testing laboratories and is addressed in EPA methods 1694 and 1698.

The accuracy of reference standards used in these tests is critical. High purity neat and certified solution standards are available from several sources.

EPA method 1694 states “If the chemical purity is 98% or greater, the weight may be used without correction to calculate the concentration of the standard.” However, this statement does not consider nonchromatographic impurities such as residual solvent, water, or trace inorganics; uncertainty associated with purity of the neat material; or how these components directly affect concentration of the analytical solution. Certain neat materials contain considerable levels of residual solvent due to the compound’s crystal structure, functional groups, or solvent of crystallization. Changes in residual water content of a neat material over time can significantly impact the concentration of analytical solutions prepared from the neat in the testing laboratory. Ampouled Certified solution Standards offer a viable and accurate alternative.

Different vendors present concentration and uncertainty information in different ways on their certificates of analysis. Understanding the certificate of analysis – what is and is not included in the reported uncertainty – and factors that impact preparation of a certified solution standard are critical to understanding the accuracy and uncertainty of the standard and the impact on testing. Understanding these variables is also important for labs seeking to comply with ISO 17025 requirements.

The preparation, uncertainty, and stability of Cerilliant Certified Snap-N-Shoot® Solution Standards for EPA Methods 1694 and 1698 will be presented. The impact of uncertainty of the neat material purity, residual water, residual solvent, and inorganic content on preparation of the solution standard and stability will be demonstrated. Comparison and explanation of uncertainty statements from a variety of certificates of analysis will also be presented.


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