as well as surrounding substances. As previously mentioned the
SIM chromatogram at m/z 124 produced the ‘‘cleanest’’ guaiacol
peak (best selectivity), but weakest signal. SIM chromatograms
employing all three major fragments produced the strongest guaiacol
peak, but were found to be unsatisfactory at low guaiacol concentrations
because of interfering mass fragments in orange juice
at m/z 81. This interference was observed with both wax and nonpolar
(DB-5) columns and several thermal gradient programs. It
can also been seen from the m/z 81 SIM chromatogram in Fig. 3
that the component that elutes just before guaiacol (tentatively
identified as isopiperitenone (3-methyl-6-(1-methylethenyl)-2-
cyclohexen-1-one)) also has a significant m/z 81 peak, as evidenced
by the elevated peak height of this peak compared to guaiacol.
Terpenes are ubiquitous in citrus juices and terpenes have a considerable
mass fragment at m/z 81. An extracted ion chromatogram
at m/z 136 (the molecular ion of terpenes) produced a small peak at
the same retention time as guaiacol, thus suggesting that coeluted
terpenes could contribute to the interfering m/z 81 signal.