In the preamble to the rule, FDA states that they agree with comments that companies should have the flexibility to decide what methods are most appropriate or suitable for testing or examining their ingredients and dietary supplements. They go on to note that the appropriateness of the test will depend on the nature of the material being testing and the manufacturer is responsible for choosing the appropriate test.
Specifically, 21 CFR 111.75 (h)(2) of the new rule states that the tests and examinations that you use have to include at least one of the following methods: gross organoleptic analysis; macroscopic analysis; microscopic analysis; chemical analysis; or other scientifically valid methods. Once again, It is your responsibility to determine the appropriateness of the test and/or examination you will use based on suitability for the material and purpose of the test. For example, an organoleptic examination of a powdered herbal extract may not be a suitable identity test, and a macroscopic and/or microscopic evaluation to confirm identity would have to be performed by personnel that have been trained and qualified to do such.
The final rule does not dictate the use of compendial or official test methods, and although the FDA recommends their use where appropriate, the actual regulatory requirement is that the test or examination be scientifically valid. In the preamble to the final GMP rule, the FDA discusses what they consider a scientifically valid test or examination. They note that although a method has not been “formally validated”, meaning that it has not been subject to collaborative studies using multiple laboratories, it may in fact be a scientifically valid method because it has been tested multiple times in a single lab and is suitable for its intended use. They also note that typical validation characteristics include accuracy, precision, specificity, detection limits, quantification limits, linearity, range and robustness. The preamble to the 2003 proposed FDA GMPs for Dietary Supplements cites several references that companies might use to conduct internal method validation studies including USP, AOAC and ICH guidance documents.