Chemical analysis of Ginkgo biloba leaves and extracts.

The chemical analysis and quality control of Ginkgo leaves and extracts is reviewed. Important constituents present in the medicinally used leaves are the terpene trilactones, i.e., ginkgolides A, B, C, J and bilobalide, many flavonol glycosides, biflavones, proanthocyanidins, alkylphenols, simple phenolic acids, 6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols. In the commercially important Ginkgo extracts some of these compound classes are no longer present. Many publications deal with the analysis of the unique terpene trilactones. They can be extracted with aqueous acetone or aqueous methanol but also supercritical fluid extraction is possible. Still somewhat problematic is their sample clean-up. Various procedures, not all of them validated, employing partitioning or SPE have been proposed. Some further development in this area can be foreseen. Separation and detection can be routinely carried out by HPLC with RI, ELSD or MS, or with GC-FID after silylation. TLC is another possibility. No quantitative procedure for flavonol glycosides has been published so far due their difficult separation and commercial unavailability. Fingerprint analysis by gradient RP-HPLC is possible. After acidic hydrolysis to the aglycones quercetin, kaempferol and isorhamnetin and separation by HPLC, quantitation is straightforward and yields by recalculation an estimation of the original total flavonol glycoside content. For biflavones, simple phenols, 6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols analytical procedures have been published but not all assays are yet ideal. Lately a there is a lot of interest in the analysis of the undesired alkylphenols and a few validated procedures have been published. The analysis of Ginkgo proanthocyanidins is still in its infancy and no reliable assays exist.