For many years, due to high prices and popularity, adulterated Ginkgo extract are commonly found on the market. 

There is growing concern in the global botanical industry regarding the adulteration of ginkgo (Ginkgo biloba) leaf concentrated extracts with exogenously derived (from other plants) free flavonols (also known as flavonol aglycones) or flavonol glycosides.  Since the official monographs (e.g., the methods of the United States Pharmacopeia-National Formulary [USP-NF] and the European Pharmacopoeia [EP]) for quality control of ginkgo extracts specify a flavonoid content of 22-27% measured by high-performance liquid chromatography (HPLC) after hydrolysis of the flavonol glycosides, it is relatively easy to bring a low-quality extract into compliance with the specified levels of flavonoid content by adding pure rutin, pure quercetin, or flavonol-rich extracts from other plant material. 

However the former USP 34 cannot avoid the adulteration since it has no limit for quercetin which can be added from other sources other than ginkgo.

The revised and newly updated USP 39 version solved the problem and request less than 0.5% quercetin in the Ginkgo extract. By testing the quercetin and other components by HPLC, together with the HPTLC method, the adulterated ginkgo extract can be easily detected and tested.

The new USP standard for the Ginkgo extract  is USP 39.

The detailed requirements/limits are listed below：
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