Page 36 - Multidimensional Chromatography

26 Multidimensional Chromatography

Figure 2.7 Gas chromatogram obtained for 500 l of diluted gasoline in n-pentane intro-
duced by concurrent eluent evaporation, using n-heptane as the co-solvent. Reprinted from
Journal of High Resolution Chromatography, 11, K. Grob and E. Müller, ‘Co-solvent effects
for preventing broadening or loss of early eluted peaks when using concurrent eluent evapora-
tion in capillary GC. Part 2: n-heptane in n-pentane as an example’, pp. 560–565, 1988, with
permission from Wiley-VCH.

(PTV) injector is carried out by opening the split valve during the transfer of the
fraction. An additional purge time is used to remove the remaining solvent from the
bed. The solvent is selectively eliminated, while the solutes are retained on the pack-
ing material. When solvent evaporation is concluded, the split line is closed before
the chamber is heated, thus allowing splitless transfer of the solutes into the column.
PTV, with solute trapping in packed beds, can be successfully applied to the transfer
of large volumes, although this method does present some disadvantages. The main
problem of injecting into a hot vaporising chamber occurs when thermally labile
compounds need to be analysed. In fact, the temperature of the injector would
decrease due to the large amount of solvent evaporating inside the chamber, and
therefore higher temperatures are necessary. Moreover, since the packed bed has a
high retention power, the chamber has to be heated above the column temperature in
order to release the solutes. However, this technique shows some advantages when
compared to the techniques that use uncoated precolumns for large sample introduc-
tion. First, wettability is not important for the retention of the liquid, and secondly,
the packing materials used for the liners are more stable than deactivated silica
tubing. In addition, packed beds retain more liquid per unit internal volume and the