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GC/MS

(1999)

*CC: column chromatography; TLC: thin layer chromatography; GC: gas chromatography; GC/MS: gas chromatography/mass spectrometry coupling; EO: essential oil; RI: retention index (Kovats indices).

*CC: column chromatography; TLC: thin layer chromatography; GC: gas chromatography; GC/MS: gas chromatography/mass spectrometry coupling; EO: essential oil; RI: retention index (Kovats indices).

Pungent principles of ginger can also be analyzed as such or as trimethylsilyl (TMS) derivatives. In the first case, after extraction using 0.85 g.L-1 supercritical CO2, the extract was directly submitted to electron-spray mass spectrometric identification. Gin-gerols and shogaols have been identified and their concentrations determined. A low concentration of shogaols is characteristic to this extraction procedure (Bartley, 1995). In the second case, Harvey (1981) reported GC/MS data for the TMS derivatives of gingerols, methyl gingerols, shogaols, methyl shogaols, paradol, gingerdiols, hydroxy-curcumins, and demethylated hexahydrocurcumin. GC/MS identification of ginger components was made by comparison of the unknown mass spectrum with a great number of mass spectra of known molecules stored on computer disks equipped with a data acquisition system that is an integral part of the instrument. Several papers, reviews, books and data banks are available (Vernin et al., 1998) (see Table 3.9).

Retention Indices as Filters (or Relative Retention Times, (aR)

Retention times (Rt) and mass spectra of unknown compounds have been compared with those of authentic standards in the earlier studies of ginger oils (Connell, 1970; Kami et al., 1972; Chen and Ho, 1987, Kim et al., 1992). However, these retention values are not reproducible and vary greatly with the temperature on a given chromatographic

Table 3.9 Compilation of selected mass spectra: reviews, books, and data banks

Books and r

Author(s) or origin (year)

Registry of mass spectral data

Qualitative analysis of flavor and fragrance volatiles by GC-MS Eight peak index of MS

Identification of essential oil components by GC-MS Monoterpene hydrocarbons

Monoterpene aldehydes and ketones Monoterpene alcohol Monoterpene esters Monoterpene derivatives

Monoterpenes Sesquiterpene hydrocarbons Sesquiterpene hydrocarbons Sesquiterpene hydrocarbons

The atlas of spectral data: Sesquiterpene hydrocarbons Isoprenoids from tobacco Essential oils

Natural and synthetic flavors and fragrances Diterpenes, terpenes, and terpenoids

Flavor and fragrance materials

Stenhagen et al. (1974) Jennings and Shibamoto (1980) Mass Spectrometry Data Centre (1983, 1986)

Adams (1995, 2001) Ryage and Von Sydow (1963), Thomas and Willhalm (1964) Von Sydow (1964) Von Sydow (1963) Von Sydow (1965) Von Sydow (1970) Yukawa and Ito (1973) Swigar and Silverstein (1981) Hirose and Buseki (1967) Hayashi et al. (1967) Moshonas and Lund (1970) Joulain and König (1998) Enzell et al. (1984) Chien (1988)

Tucker and Maciarello (1994) Enzell et al. (1965, 1966, 1967, 1969, 1972, 1980)

Colon and Vernin (1998)

Databases

Author(s) or origin (year)

EPA-NIH mass spectral database

NBS library compilation PBM database

CD-ROM and DC-ROM systems for mass spectral data Database on essential oils

Compilation of mass spectra of volatile compounds in foods Wiley/NBS registry of mass spectral data Bench-top/PBM version 3.0 MPI library of mass spectral data NIST/EPA/NIH mass spectra database

Heller and Milne (1978, 1980, 1983, 1987)

Finnigan Mat (1984) Hewlett Packard (1988) Wiley and Sons (1988) Chien (1988)

De Brauw et al. (1981, 1988) McLafferty (1988, 1989) McLafferty (1988) Henneberg et al. (1989) National Institute of Standards and Technology (1992)

column. Kovats indices (KI) do not suffer from this disadvantage (Kovats, 1958, 1965). At isothermic temperature, Kovats uses the following logarithmic equation with linear alkanes as reference compounds:

where t'R(x), t'R(n), t'R(n+1) are the reduced retention times (tR — tm) of the unknown compound and the linear alkanes with n and n + 1 carbon atoms, respectively, which are eluted just before and after compound x. (tm) is the retention time of the air or that of the more volatile solvent such as pentane. Their reproducibility on polar (Carbowax 20 M, DB-Wax, FFAP, BP 20, HP 20) and nonpolar columns (SE 30, SF 96, OV 1, OV 101, OV 117, DB 1, DB 5) is good under similar GC conditions on a given column.

In linear programmed temperature, which is the usual case, Van den Dool and Kratz (1963) used the following formula :

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