Two species of spearmint oil (mentha spicata and mentha gracilis) are cultivated in the United States. In 2008, 1.09 million kilograms of spearmint oil were produced in the US (1). Approximatley, 45% of mint oil produced in the US is used to flavor chewing gum. One 55-gallon drum of mint oil can flavor 5,200,000 sticks of gum or 400,000 tubes of toothpaste (2).
Spearmint oil is stored in glands on the underside of leaves. Mature mint plants are cut and left to dry before being chopped and transferred to a distillery. Pressurized steam vaporizes the mint oil, which passes through a condenser to be collected as a liquid. A separator takes mint oil from the liquid and transfers it into drums that are placed in a temperature-controlled warehouse. Essential oil companies test samples at this point to decide whether to purchase the oil. Gas chromatography is commonly used to assess oil quality. Oils containing impurities may undergo rectification, a re-distillation step used to purify the oil.
Volatile sulfur compounds impart undesirable odors to essential oils and have extremely low olfactory thresholds. Essential oil companies require a rapid screening technique to detect and quantify volatile sulfur compounds.Experimental Conditions
Instrumentation used in this study was an Agilent 7890A GC equipped with an OI Analytical 5380 Pulsed Flame Photometric Detector. Two different samples of neat spearmint oil were tested. The identity of sulfur compounds in the sample was unknown, only suspected.
The study demonstrated that low-level sulfur compounds can be detected and isolated in spearmint oil using an OI Analytical 5380 PFPD detector, dual integration time gates, and comparative carbon peak matching with FID chromatograms.
(1) V.D. Zheljakov, C.L. Cantrell, T. Astatkie, and M.W. Ebelhar, "Productivity, Oil Content, and Composition of Two Spearmint Species in Mississippi," Agronomy Journal, Vol. 102, Issue 1 (2010).
(2) Mint Industry Research Council, http://www.usmintindustry.org/.
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