**Chen-Yu Qian 1,2, Wen-Xuan Quan 2, Zhang-Min Xiang 1,\* and Chao-Chan Li 2,\***


Academic Editor: Igor Jerkovi´c

Received: 14 August 2019; Accepted: 11 September 2019; Published: 12 September 2019

**Abstract:** Volatile compounds in flowers of *Rhododendron delavayi*, *R. agastum*, *R. annae*, and *R. irroratum* were analyzed using comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC) coupled with high-resolution quadrupole time-of-flight mass spectrometry (QTOFMS). A significantly increased number of compounds was separated by GC×GC compared to conventional one-dimensional GC (1DGC), allowing more comprehensive understanding of the volatile composition of *Rhododendron* flowers. In total, 129 volatile compounds were detected and quantified. Among them, hexanal, limonene, benzeneacetaldehyde, 2-nonen-1-ol, phenylethyl alcohol, citronellal, isopulegol, 3,5-dimethoxytoluene, and pyridine are the main compounds with different content levels in all flower samples. 1,2,3-trimethoxy-5-methyl-benzene exhibits significantly higher content in *R. irroratum* compared to in the other three species, while isopulegol is only found in *R. irroratum* and *R. agastum*.

**Keywords:** *Rhododendron* flowers; volatile compounds; comprehensive two-dimensional gas chromatography-mass spectrometry; quadrupole time-of-flight mass spectrometry; odor description
