ABSTRACT
The efficiency of using combinations of retention indices and partition coefficients (Kp) with a hexane: acetonitrile system has been demonstrated by taking as an example the essential oil from Artemisia pallens Wall. Preliminary partition of the components between the two partly mixing liquids provides information by which components can be attributed to the appropriate homologous series. The use of group constants (j), which are functions of both partition coefficients and GC retention indices, in the practice of identifying the components of essential oils is reported for the first time.
Subject(s)
Chromatography, Gas/methods , Oils, Volatile/analysisABSTRACT
Partition coefficients (Kp) in a heterogeneous system consisting of two immiscible organic solvents can be successfully used for a supplementary identification parameter in qualitative GC and GC-MS analysis of organic compounds. For rapid addition to database of Kp values, calculation methods based on the well-known 'retention-structure relationships' approach can be used. This paper reports the experimentally determined and calculated Kp values for 252 compounds including alkyl aromatic hydrocarbons and esters. It is shown that for group identification of components it is desirable to use not the Kp values themselves but the parameter j which is a combination of K, and gas chromatographic retention indices: j = kI - log Kp.
Subject(s)
Esters/chemistry , Hydrocarbons, Aromatic/chemistry , Acetonitriles/chemistry , Hexanes/chemistryABSTRACT
Branched hydrocarbons were identified in the lipids ofLeptinotarsa decemlineata Say andTribolium destructor by gas chromatography, ordinary electron impact mass spectrometry, and linked, scanned, daughterion monitoring. This methodology allowed us to revise our earlier results based only on GC-MS data confirming the existence of only monomethyl-, dimethyl-, and trimethylalkanes in the hydrocarbons ofL. decemlineata Say. The hydrocarbons fromTribolium destructor consist ofn-alkanes, 3-methylalkanes, internally branched monomethylalkanes and dimethylalkanes. Daughter-ion monitoring can be particularly important for distinguishing between incidentally overlapped GC peaks of hydrocarbons from different series. A trace, for example, of dimethylalkane coeluating withn-alkane was easily identified in GC peak of hydrocarbon mixture ofT. destructor. Link scans confirmed also molecular weights for the compounds without molecular ions in the mass spectra. Structural assignment of the compounds were verified by comparison of the experimental and calculated values of the GC retention Kovats indexes (KI).
