Characterization of Volatile Compounds in Four Different Rhododendron Flowers by GC×GC-QTOFMS

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; comprehensive two-dimensional gas chromatography-mass spectrometry; odor description; quadrupole time-of-flight mass spectrometry; volatile compounds.

Figure 1

Chromatographic analysis of Rhododendron by GC-quadrupole time-of-flight mass spectrometry (QTOFMS) and a comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC)-QTOFMS color diagram (1: linalool; 2: 2-nonen-1-ol; 3: linalool oxide; 4: p-cymenene; 5: benzoic acid, methyl ester).

Figure 2

Diagram illustrating the process of compound confirmation in GC×GC-QTOFMS.

Figure 3

Distribution (%) of major compounds presented in four different species of Rhododendron.

Figure 4

Distribution of the chemical classes for Rhododendron (AH: aromatic hydrocarbons).

Figure 5

Proportions of odor compounds in Rhododendron.