Instant Notes: Analytical Chemistry

(Tina Meador) #1
Mixtures of fragrances are readily analyzed. Figure 2 shows the TIC
chromatogram of a mixture of six fragrance components, injected as 5 ml of a
solution in ether.

296 Section F – Combined techniques


100 200 300

79

119
160

183

257

278

Signal

Time (s)

Fig. 2. TIC chromatogram of fragrance mixture using a BP-1, nonpolar capillary column,
direct injection and MS.

The large peak at low retention time is the solvent. The solute peaks are
readily identified, either by consideration of their retention index and mass
spectral fragmentation patterns, or directly by computer searching.
The mass spectrometer scan at 160 seconds, which corresponds to a boiling
point of about 220°C, gave the major peaks listed in Table 1.

Table 1. Mass spectrometric peaks for peak at 160 s
m/z Relative intensity % Assignment
39 55 C 3 H 3 +
65 30 C 5 H 5 +
92 90 (M−CH 3 COOH)+
120 100 (M–CH 3 OH)+
152 50 M+, C 8 H 8 O 3

This suggests a methyl ester of an aromatic acid, and the spectrum matches
the mass spectrum of methyl salicylate, present in oil of wintergreen (Fig. 3).
Peaks 5 and 6 give almost identical mass spectra and may be identified as
isomers of eugenol, present in oil of cloves. The higher boiling isoeugenolis
probably the peak at 278 s.
This spectrum does not correspond to any likely essential oil or fragrance, but
may be identified as a contaminant. Many of the fragment ions are separated by
a constant mass difference of 14. This suggests a long-chain aliphatic compound,
possibly a hydrocarbon. A molecular ion at m/z 156 would correspond to C 11 H 24 ,
and this component matches the spectrum of n-undecane.
Other applications include the analysis of alcoholic drinks, such as whisky, of
pesticides from environmental samples (e.g., chlorinated pesticides from marine
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