Doi: 10. 1016/j chroma

2. Volatile compounds

The commonly used extraction methods for the volatile compounds of TCMs include steam distillation and lipophilic organic solvent extraction. Using steam distillation, the essential oils of C. salsa and C. tubulosa were extracted, and 38 and 21 components were identified by GC–MS, respectively (Table 1). The main constituents in the essential oils of C. salsa consist of alkanes, alcohols, aldehydes and some heterocyclic compounds, while palmitic

Table 1

Analysis of volatile compounds in Cistanche species by GC–MS

Species	Extraction method	Number of identified compounds	Ref.
C. salsa	Stream distillation	38 (70%)^a	[22]
C. tubulosa	Stream distillation	21(91.44%)	[23]
C. deserticola	Petroleum ether extraction	25(75.03%)	[24]
C. deserticola	Simultaneous distillation-extraction	24(83.60%)	[25]
C. salsa	Supercritical fluid extraction (SFE)	35^b	[26]

^a Relative content of the identified compound in the total volatile components. ^b Not mentioned in the original literature.

Table 2

The number of various chemical constituents from Cistanche species

Species	Benzyl glycosides	Phenylethanoids	Iridoids	Ligans
C. deserticola	/	17	10	3
C. tubulosa	/	20	10	5
C. salsa	3	11	/	/
C. sinensis	/	3	/	/
C. phelypaea	/	5	4	/

acid and linoleic acid are the two major constituents of the total oils of C. tubulosa [22,23]. The volatile compounds of C. deserticola were extracted by petroleum ether, and 25 constituents were identified by GC–MS. The three richest constituents are methyl 14-methylpentadecanoate (13.61%), ethyl palmitate (12.39%) and 2,5,6-trimethyloctane (7.60%) [24]. Another report on the volatile components of C. deserticola showed that eugenol was the main component, when using a simultaneous distillation-extraction method [25]. The different analytical results of these two papers [24,25] might be caused by different extraction methods and different analytical conditions of GC–MS.
Besides these, Ma reported a supercritical fluid extraction (SFE) method to extract the non-polar constituents from C. salsa. The analysis of the extract by GC–MS showed some esters and low molecular compounds containing oxygen or nitrogen existing, besides the alkanes. This result demonstrated that more polar compounds could be extracted by SFE through the addition of polar modifier [26].