Determination of Enantiomer Ratios of d,l-Carvone in Supercritical Fluid Extracts from Caraway Seeds and Speamint Leaves by High-Performance Liquid Chromatography with Polarimetric and Ultraviolet Spectrophotometric Detection

Abstract

KeywordsEnantiomer ratio, d,l-carvone, caraway seeds, speamint leaves, polarimetric detector, supercritical fluid extractionThe determination of enantiomer ratios of optical isomers has been an important subject in pharmaceutical chemistry, biochemistry, clinical chemistry, and agricultural chemistry because the optical isomers often differ in biological activity.There are two methods for the determination of enantiomer ratios by high-performance liquid chromatography (HPLC). One employs the chromatographic enantiomer separation which can be achieved either by using a chiral stationary phase or chiral mobile phase or by derivatization into diastereomers. The other is based on the simultaneous detection of optical rotation and UV absorption. In the latter method, the apparent optical rotation representing the sum of optical rotations of d and l-type, and the UV absorption representing the total amount, are measured by polarimetric detector and UV detector, respectively. The d/ l ratio can be obtained from a calibration curve established by the response of the polarimeter and the UV detector for a known amount of d-or l-isomer. Here one assumes the response of the polarimeter becomes zero when d/1=1, whereas that of the UV detector is simply proportional to the total amount.An advantage of this method over the first one is that chromatographic separation of optical isomers is not necessary.Therefore, this method is quite useful when enantiomer separation is difficult. Thus, the strategy has been employed in the determination of enantiomer ratios of permetric acid pentafluorobenzylesterl, d,/-epinephrine2, pyrethroids3, amino acids4, and DP-1904.5 In this report, the compositional ratios of d-and 1-enantiomers of carvone in essential oils were determined by HPLC with simultaneous detection of optical rotation and UV absorption.Essential oils were extracted from caraway seeds and dry speamint leaves by supercritical fluid of carbon dioxide.Caraway seeds contain 100% d-carvone and speamint leaves contain 93% l-carvone and 7% d-carvone. Experimental ApparatusThe HPLC system consisted of a JASCO Model LC-800 series, which included an 880-PU pump, a Rheodyne 7125 injection valve, an 860-CO air circulating oven, an 870-UV variable wavelength UV detector and an 807-IT data processor. Chromatograms were recorded on a RC-250 dual-pen recorder. A DIP-181C polarimeter (JASCO) was used for polarimetric detection. A polarizes and an analyzer used in the polarimeter were made of glam-Thomson prisms. A high pressure mercury lamp was used as light source without a filter. The flow cell had a 50 mm light-path length with an internal volume of 350 µl. A supercritical fluid extraction and chromatography system, JASCO Model Super-200, was employed in the extraction for essential oils from samples. Fig. 1 Structures of carvone enantiomers.

Determination of essential oil content in caraway (Carum carvi L.) species by means of supercritical fluid extraction

“…In SFE, carbon dioxide is used predominantly (Engelhardt and Gross 1988, Bounoshita et al 1993, Kallio et al 1994) because of its low critical temperature (31°C) and low critical pressure (7.38 MPa), negligible toxicity, incombustibility and low reactivity. Its polarity and extraction power are close to n-hexane.…”

Supercritical fluid extraction as a tool for isolation of monoterpenes from coniferous needles and walnut-tree leaves

“…Water steam distillation was performed in apparatus according to ČSN 58 0110 [5]. The milled plant material (c. 10 g ± 5 mg) was transferred quantitatively into the 1 l glass bottle and 400 mL of water was added.…”

“…Thus the characteristics of mass transport in gaseous phase are combined with the very high solvation properties of liquids [1]. Carbon dioxide is one of the most commonly used supercritical fluids for SFE [3][4][5] due to its very low critical temperature (31 o C) and pressure (7,38 MPa), zero toxicity, flame resistance and low reactivity. Its polarity and extraction strength is comparable with n-hexane whereas its extraction efficiency decreases with increasing polarity of analytes.…”

Determination of essential oils content and composition in caraway (Carum carvi L.)

“…Supercritical fluid extraction (SFE) of essential oils is a dynamically developing extraction technique that is a very good alternative to the classical extraction procedures using organic solvents. Supercritical carbon dioxide (polar modifiers like methanol, acetone, etc., are applied to increase polarity of the fluid) is the most widely used supercritical fluid in analytical SFE (KALLIO et al 1994;ENGELHARDT & GROSS 1988;BOUNOSHITA et al 1993), having low values of critical temperature (31°C) and pressure (7.38 MPa). Gas chromatography with FID or MS detectors is mostly used to determine carvone, limonene and other constituents.…”

“…Liquid chromatography with UV or polarimetric detection (KOVAR & BOCK 1983), derivative spectrophotometry in UV (SEIF EL DIN et al 1983) and proton magnetic resonance (MOSSA et al 1980) can be alternatively applied. Chromatographic methods allow the separation of enantiomers of carvone (BOWMEESTER et al 1995;KALLIO et al 1994;BOUNOSHITA et al 1993;RAVID et al 1992), limonene (BOWMEESTER et al 1995) and other constituents (KALLIO et al 1994), as well as the determination of origin by the so-called "finger-print" method (THIES 1984). Collection of GC chromatograms of different essential oils and MS spectra of many monoterpenes are available in a review and a book (MASADA 1976;Analytical Method Committee 1988).…”