Internal Standard

1. The terpene composition of an essential oil can be determined using gas chromatography-mass spectrometry. 

A 5.00 ml sample of essential oils is spiked with 500.0 mL of 100.0 ppm n-decane as an internal standard and diluted to the mark in a 10.0 mL volumetric flask. A 10.0 mL portion of the mixture is injected into the GC-MS and the peak areas recorded to determine the concentration of limonene. A series of standards containing n-decane and limonene were also analyzed by the same method. The following results were obtained:

Concentration of Limonene (ppm)     peak area limonene                 peak area n-decane

1.0 ppm                                             540                                         5,566

5.0 ppm                                             2,791                                      5,570

10.0 ppm                                           5,570                                      5,542

15.0 ppm                                           8,112                                      5,564

20.0 ppm                                           10,786                                    5,558

Essential Oil Unknown                          1,055                                      5,549

Determine the concentration (in ppm) of limonene in the essential oil.