Question

5. Below is a table showing composition data for clove oil, obtained using two different detection methods (with the same sample), FID and mass spectrometry. Explain why the composition (based on relative peak areas of the GC trace) is different for these data sets. Are either of these the “real” composition of the clove oil?

Hint: Response factor

	FID		MS detector
	Area	Area%	Area	Area%
Eugenol	86.78	87.73	137.95	75.84
Caryophyllene	2.03	2.05	10.26	5.64
Eugenol Acetate	10.11	10.22	33.68	18.52

Answer 1

Gas chromatography is a analytical separation technique to analyse volatile substances in the gas phase. There are several kind of detectors used in Gas chromatography such as mass spectrometry detectors which scans the masses continuously throughout the separation. Once the sample exists the column it moves to the inlet of the mass spectrometer where it is ionized and fragmented. During which the sample is bombarded with energetic electrons which ionize the molecule, further bombardment causes the ions to fragment. These ions are passed into a mass analyse where the ions are sorted according to their mass-to-charge ratio.

The composition on relative peak areas of the Gas Chromatography is different in these data sets because the physical properties of action of FID and MS are different.
The Flame ionization detection( FID) is a detector for organic compound in Gas Chromatography that detects the amount of carbon in a sample. In this technique the samples are burned in a hot hydrogen-air flame. Due to this combustion carbon ions are produced. The total amount of ions is directly proportional to the amount of carbon in the sample while the chromatogram of the mass spectrometry is based on the intensity of fragments produced by the ionization. Some compounds such as clove oil give a low fragmentation in Mass spectrometry but high signals in FID

There are 3 different clove oil - bud , leaves and stem differ in their composition. For example the proportion of eugenol is highest in stem oil and least in the bud oil. It is not mentioned in the question as to whether results are of bud oil/ leaves oil/ stem oil and hence it is difficult to tell whether the composition mentioned is of " real clove oil". However the real composition of olive oil is as follows.

Bud oil: 60-90% eugenol, 4-15% eugenyl acetate and Beta-caryophyllene and other minor costituents.

Leaf oil : 82-88% eugenol, Beta- caryophyllene

stem oil : 90-95% eugenol with other minor constituents.

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