testing dietary supplements

My experience with dietary supplements is that analysis of products with multiple ingredients, especially those at low concentrations, is very difficult and requires experience with the particular supplement matrix (formula plus excipients). Random testing of products off the shelf is fraught with technical difficulties. In addition, many ingredients lack standard, universally accepted testing methods within a dietary supplement matrix, which can result in confusion. These are sophisticated issues, whose resolution sometimes is difficult for anyone trying to ascertain product quality based on limited testing and lack of relevant experience. That is why most labs prefer to test single ingredient products, a tacit admission of the uncertainties involved in testing complex formulations. Testing is not as black and white as news releases often indicate or imply. Further, extrapolation of analytical results to nutrition, health and safety issues also requires expertise in these sometimes controversial areas, which very few labs have. It is important to verify label claims, but sometimes the manufacturer's validated procedures for qualification of an individual ingredient - combined with appropriate quality controls to assure that a proper mixture has been made - may more accurately represent the quality and quantity of that ingredient in a formula than any lab results obtained by applying a single analytical test to vastly different formulations containing that ingredient.