Microwave irradiation followed by zinc oxide based dispersive
solid-phase extraction coupled with HPLC for simultaneous extraction
and determination of flavonoids in Veronicastrum latifolium (Hemsl.)
Yamazaki

Received: 4 September 2018 /Revised: 6 November 2018 /Accepted: 29 November 2018
# Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract
In this study, a sample preparation method involving microwave irradiation followed by dispersive
solid-phase extraction wasused to extract and separate flavonoids from Veronicastrum latifolium (Hemsl.)
Yamazaki. Ethyl lactate was selected as the extraction solvent during microwave irradiation. Zinc
oxide and ethanol were used as the adsorbents and the eluent, respectively, in dispersive solid-phase
extraction. Several experimental parameters affected the extraction performance, such as the extraction
solvent and method, the microwave irradiation time, temperature, and solid-to-liquid ratio, the type of
adsorbent, the amount of sample solution, the adsorption time and method, and the type and volume
of the eluent, and were investigated by single-factor and Box–Behnken design experiments in the
pretreatment process. The recommended method was applied to extract flavonoids  in Veronicastrum
latifolium (Hemsl.) Yamazaki. The enriched flavonoids were analyzed for the first time by high-performance
liquid chromatography, and seven flavonoids—vitexin, luteolin, wogonoside, apigenin, chrysoeriol,
acacetin, and pectolinarigenin—were identified. Additionally, the method exhibited good linearity
(r2 ≥ 0.9992) for flavonoids under the optimum conditions. Moreover, the relative standard deviation
of the intraday and interday precision was less than 3.97%. The mean recoveries for flavonoids were
more than 98.10%. This work is the first to report a method to extract, separate, and analyze flavonoids
from Veronicastrum latifolium (Hemsl.) Yamazaki. Keywords Ethyl lactate . Microwave-irradiation
extraction .Zinc oxide . Dispersive solid-phase extraction . Veronicastrum latifolium (Hemsl.)
Yamazaki . High-performance liquid chromatography

Experimental
Reagents and materials

V. latifolium was purchased from the medicinal herb wholesale market in Bozhou (China).
Acetonitrile, methanol, ethanol, and other solvents used were of HPLC grade and were  purchased
from J.T. Baker (Phillipsburg, USA). Vitexin (purity 98.0% or greater), luteolin (purity 98.0% or
greater),wogonoside (purity 98.0% or greater),apigenin (purity98.0% or greater), chrysoeriol
(purity 98.0% or greater),acacetin (purity 98.0% or greater),and pectolinarigenin (purity 98.5%
or greater) flavonoid standards were purchased fromChengdu Alfa BiotechnologyCo. (Sichuan,
China).Phosphoric acid (H3PO4) of chromatographic grade and ethyl acetate was