Gao, Jiayu, et al. “Validation of a HPLC Method for Flavonoid Biomarkers in Skullcap (Scutellaria) and Its Use to Illustrate Wide Variability in the Quality of Commercial Tinctures”. Journal of Pharmacy & Pharmaceutical Sciences, vol. 11, no. 1, Mar. 2008, pp. 77-87, doi:10.18433/J39G6V.