HPLC-UV Flavonol Fingerprint Allows Detection of Ginkgo Adulteration

Reviewed: Ma Y-C, Mani A, Cai Y, et al. An effective identification and quantification method for Ginkgo biloba flavonol glycosides with targeted evaluation of adulterated products. Phytomedicine. 2016;23(4):377-387.

The adulteration of commercial products labeled to contain Ginkgo biloba (Ginkgoaceae) extracts has been the subject of a number of publications.¹ This paper describes a high-performance liquid chromatography–ultraviolet spectrophotometry (HPLC-UV) fingerprinting approach to authenticate commercial ginkgo extracts and finished products. The authors, including scientists from the Canadian Phytopharmaceuticals Corporation, developed and validated a method to separate ginkgo flavonol glycosides and aglycones in 14 min. This method was then used to analyze whole ginkgo leaves (n=13), bulk standardized ginkgo leaf extracts (n=15), and commercial finished products (n=14). The whole ginkgo leaves were harvested in several areas in China (Shandong, Sichuan, Hubei, and Henan provinces). The powdered bulk extracts were received from various Canadian suppliers, and commercial finished product samples were purchased in local pharmacies in Canada (n=7) or China (n=7).

The 13 largest peaks in the chromatograms were used for comparison among the samples and for subsequent statistical evaluation. This comparison evidenced that three standardized extracts and 10 commercial samples had unusually high amounts of the aglycones quercetin, kaempferol, and isorhamnetin. In addition, one extract was composed primarily of rutin. The occurrence of adulteration in these 14 samples was confirmed by subsequent principal component analysis, where all the samples clustered separately from the authentic samples, thus confirming adulteration in four out of 15 (27%) standardized extracts and 10 out of 14 (71%) commercial products. One commercial product showed a similar composition to the authentic ginkgo materials, and clustered with the authentic samples in the chemometric evaluation, but was nevertheless considered by the authors to be spiked with a flavonol glycoside.

Comment: This paper presents another fingerprinting method as an alternative to compendial methods, e.g., those in the United States Pharmacopeia,^{2 to detect ginkgo adulteration. The sample preparation is simple, and the authors present the shortened analysis time, and the ability to measure rutin, quercetin, kaempferol, and isorhamnetin in one run as the major advantages of this method. The use of statistical data to evaluate adulteration is helpful, and allows a more objective comparison of the sample with authentic material than reliance on the analyst’s expertise. These results support findings from previous publications4,5} demonstrating that adulteration of ginkgo products is still prevalent.

There are a few inconsistencies in the paper that are worthy of note; for example, the number of adulterated samples is stated to be 90%, but this is not supported by the results. In the abstract, the run time is written as 13 min., while according to the materials and methods section, it is 14 min., with a 5 min. washout period and another 14 min. to equilibrate the column (a run time of 13 min. was confirmed by one of the authors [Y-C Ma oral communication, March 18, 2016]). Also, it is unclear if some of the mass spectrometric data presented, e.g., the [M+H]⁺ ion for quercetin (which has a molecular weight of 302.2357 u) at m/z = 304.9 and the [M-H]^- ion at m/z = 302.9, are typing errors, if the ions are actually due to a different compound with a molecular weight of approximately 304 u, or if the mass spectrometer was not well calibrated.

References

1.     Gafner S. Ginkgo extract adulteration in the global market: a brief review. HerbalGram. 2016;(109):58-59. Available at: http://cms.herbalgram.org/herbalgram/issue109/hg109-qualcontrol-ginkgo.html. Accessed May 10, 2016.

2.     United States Pharmacopeial Convention. Ginkgo biloba. In: United States Pharmacopeia and National Formulary (USP 38–NF 33). Rockville, MD: United States Pharmacopeial Convention; 2015.

3.     The European Directorate for the Quality of Medicines & HealthCare. European Pharmacopoeia (EP 8.7). Ginkgo folium. Strasbourg, France: Council of Europe; 2015.

4.     Wohlmuth H, Savage K, Dowell A, Mouatt P. Adulteration of Ginkgo biloba products and a simple method to improve its detection. Phytomedicine. 2014;21(6):912-918.

5.     Avula B, Sagi S, Gafner S, et al. Identification of Ginkgo biloba supplements adulteration using high performance thin layer chromatography and ultra high performance liquid chromatography-diode array detector-quadrupole time of flight-mass spectrometry. Anal Bioanal Chem. 2015;407(25):7733-7746.