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On July 21-22, 2009, at AOAC headquarters in Gaithersburg, Maryland, USA, expert review panels (ERP) evaluated 25 of the most promising methods purported to meet fitness-for-purpose for cranberry and milk thistle analyses in dietary supplements. All reviewed methods were collected by AOAC as a result of a call for methods and experts. As part of an NIH/FDA/AOAC initiative on dietary supplements, candidate methods for cranberry and milk thistle were recommended, with modifications, by the ERP for further evaluation and validation. For cranberry, the ERP, chaired by David Cunningham, Ocean Spray Cranberries, Inc., selected a method by Paula Brown of the British Columbia Institute of Technology, which met the criteria required by the fitness-for-purpose statement and criteria developed by the panel for a suitable candidate method. The method uses HPLC-DAD instrumentation readily available to most laboratories; can determine five cranberry anthocyanins (four major and one minor); shows good separation with reasonable run time; has a simple non-SPE sample preparation; uses a highly efficient extraction solvent (MeOH-HCl); and uses a commercially available mixed anthocyanin reference standard. In addition, the original SLV, conducted according to AOAC guidelines, was suitable for the four major anthocyanins. Thus, the method was recommended by the ERP for further validation, with possible modifications (after further investigation) for column, matrixes, and source of reference standards. An ERP for milk thistle, chaired by Mark Anderson, Triarco, reached consensus on a method from INA, with modifications, for further evaluation and validation. The method is supported by existing validation data (linearity, limits of detection and quantitation, precision, and extraction efficiency) from three laboratories. The ERP also recommended the method for its fitness-for-purpose, fast chromatography, and baseline separation of eight compounds. However, peak identification is based only on retention time, and the method is applicable only to milk thistle extracts and ground milk thistle fruit. In addition to other modifications, the range of matrixes must be expanded. The ERP also recommended analytes and samples to be used in validation studies, including milk thistle powdered seed, powdered seed extract, and representative finished products containing either or a combination of both. Previously, in 2004, AOAC had established a working group to address the needs of the cranberry industry, co-chaired by Mark Brudnak of MAK Wood, Inc. and Cunningham. A great deal of interest was shown early on, and the working group immediately recognized that there were many and diverse competitive priorities. Thus, the Cranberry Working Group comprised three subgroups: proanthocyanin, anthocyanin, and organic acids. Analytical methods were collected and evaluated in all three areas, and some work was initiated for anthocyanin and organic acids. Candidate methods for cranberry and milk thistle are recommended by ERPs as the best potential methods to undergo further evaluation and validation (single laboratory and multilaboratory). These methods are based on fitness-for-purpose, applicability to the scope needed, and clarity of method description. For more information, contact Bob Rathbone, senior director, publications and method validation and evaluation, at rrathbone@aoac.org or Al Pohland, chief scientific officer, chemistry, at apohland@aoac.org. Full coverage is scheduled for the September/October 2009 issue of Inside Laboratory Management.
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