Full Article Determination of Compounds in Eucommia ulmoides Oliv.Bark and Its Fermentation Products via Headspace Gas Chromatography-ion Mobility Spectrometry Zhihong Wang, a,b Mijun Peng, a, * Zhigang She, b, * Yu Qiu, a Qiuling Yang, a Minglong Zhang, a Tao Huang, a