High-speed GC and GC/time-of-flight MS of lemon and lime oil samples

The high-speed GC separation and MS characterization of lime oil and lemon oil samples using programmable column selectivity and time-of-flight mass s pectrometry is described. The volatile essential oils are separated on a se ries-coupled (tandem) column ensemble consisting of a polar trifluoropropyl methyl polysiloxane column and a nonpolar 5% phenyl dimethyl. polysiloxane column. Both columns are 7 m long. A 50 degreesC/min linear temperature ram p from 50 to 200 degreesC is used, giving an analysis time of similar to2.5 min. A time-of-flight MS with time array detection and automated peak find ing and characterization software was used to identify 50 components in lim e oil samples and 25 components in lemon oil samples. Despite numerous case s of extensive peak overlap, spectral deconvolution software was very succe ssful in the characterization of most overlapping peaks. For cases where a more complete chromatographic separation is desirable, the tandem column en semble is operated in the first-column stop-flow mode to enhance the separa tion of selected overlapping clusters of peaks. A valve between the junctio n point of the tandem column ensemble and a source of carrier gas at the GC inlet pressure is opened for 2-5-s intervals to stop the flow of carrier g as in the first column. This is used to increase the separation of target c omponent groups that overlap in the ensemble chromatogram without first-col umn stop-flow operation. This procedure is used to isolate the peak for lim onene, the largest peak in the analytical-ion chromatogram. of both the lim e and lemon oil samples.