Characterization of the Steam Nonvolatile Residue of Bergamot Oil and Some Other Essential Oils

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Abstract
A method is presented for identifying and estimating the coumarins and furocoumarins present in bergamot oil and four other essential oils. Solutions of the nonvolatile residue of the oils are spotted on silica gel thin layer plates and developed in hexane-ethyl acetate (75+25) for 4 hr. The separated compounds are identified by their Rf values and characteristic fluorescence under short wave UV light; the spots are marked, scraped from the plate, and extracted with chloroform. The centrifuged extracts are scanned in a recording spectrophotometer from 400 to 240 mμ. Bergaptene, citroptene, bergamottin, and 7-methoxy-5-geranoxycoumarin were also individually estimated. Bergaptol, isopimpinellin, and xanthotoxin could be estimated only roughly because of low absorbance readings or lack of standards. A procedure to isolate and purify bergamottin from bergamot oil and 7-methoxy-5-geranoxycoumarin from lime oil, to serve as reference standards, is also included.

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