Table 1.

Major volatile constituents of a pentane extract of the common milkweed, Asclepias syriaca, as determined by gas chromatography–mass spectrometry, and quantities used in a synthetic mimic

COMPOUNDa	Relative retention indexb	Diagnostic EI-MS fragment ions (% intensity)	Synthetic blend (μg/ml)
(E)-β-Ocimene	1124	77(36), 79(42), 91(53), 93(100)	6.14c
Benzaldehyde	1155	51(54), 77(100), 105(88), 106(88)	3.27
Nonanal	1220	29(66), 41(100), 56(61), 57(94)	4.14
Benzyl alcohol	1236	77(85), 79(100), 107(59), 108(75)	4.58
Phenylacetaldehyde	1257	65(22), 91(100), 92(24), 120(16)	11.25
(E)-2-Nonenal	1304	29(56), 41(100), 55(80), 70(58)	2.12

^aIdentity established by comparison to authentic standard of each compound

^bGC retention times relative to n-alkane standards on a Phenomenex ZB-50 column phase

^cSynthetic β-ocimene contained a 3:1 (E:Z) isomer mixture