relative retention of these reference substances is less regular, only a strict interpolation but no extrapolation is allowed.
General Note
Providing the same column film, the GC retention index of a given substance
is always the same and, consequently, can be used as first evidence for
compound identification.
Case example: How to calculate a Kovats index
This example exemplifies how to calculate a Kovats index for given gas
chromatographic data of an isothermal measurement. The measured data are
as follows:
(continued)
Lee Index
reference system consists of aromatics and PAHs, valid
for temperature programmed measurements:
benzene: 100; naphthalene: 200; phenanthrene: 300;
chrysene: 400; picene: 500
retention time
index
Benzene
Naphthalene
Phenanthrene
Chrysene
substance
400
300
200
100
Fig. 4.12 The concept of the Lee index
4.1 High Performance Chromatography: GC, HPLC
51