Organic compounds in soils 49
Figure 2.3 Cutaway view of cyrofocus trap (Source:Author’s Own Files).
advanced Cryofocusing trap mounted in a special housing that allows the sample to
be refocused on-column with outstanding results [304].
The thermal gradient is maintained in all phases of operation. This ensures that in
the cycrotrap the sample is always moving from a hotter to a colder region. As they
move through the trap the solutes are subjected to an increase in their distribution
constants. Solutes at the front of the sample band will move slower than solutes at
the rear. This allows the rear portion of the sample band to ‘catch up’ to the front,
effectively compressing the sample band into a very tight slug. With proper establishment of the gradient, heat-up rate of the cycrotrap becomes relatively unimportant. No
differences in chromatographic efficiency have been observed for heat-up rates from
100–200
◦ C/min. Figure 2.4 illustrates a sample chromatogram obtained on a thin film
(0.25 micron), narrow bore (0.20 mm) column. This therefore represents a ‘worst case’
scenario, as wider bore and thicker film columns are easier to work with.
Perhaps the greatest limitation of previous generations of Cryofocusing traps was
the requirement for the use of an uncoated precolumn in the trapping zone. Operating in this manner simplified design problems, and made precise temperature control
of transfer lines unimportant. However, the absence of any liquid phase limited the
trapping mechanism to simple condensation. Highly concentrated or extremely volatile
Figure 2.3 Cutaway view of cyrofocus trap (Source:Author’s Own Files).
advanced Cryofocusing trap mounted in a special housing that allows the sample to
be refocused on-column with outstanding results [304].
The thermal gradient is maintained in all phases of operation. This ensures that in
the cycrotrap the sample is always moving from a hotter to a colder region. As they
move through the trap the solutes are subjected to an increase in their distribution
constants. Solutes at the front of the sample band will move slower than solutes at
the rear. This allows the rear portion of the sample band to ‘catch up’ to the front,
effectively compressing the sample band into a very tight slug. With proper establishment of the gradient, heat-up rate of the cycrotrap becomes relatively unimportant. No
differences in chromatographic efficiency have been observed for heat-up rates from
100–200
◦ C/min. Figure 2.4 illustrates a sample chromatogram obtained on a thin film
(0.25 micron), narrow bore (0.20 mm) column. This therefore represents a ‘worst case’
scenario, as wider bore and thicker film columns are easier to work with.
Perhaps the greatest limitation of previous generations of Cryofocusing traps was
the requirement for the use of an uncoated precolumn in the trapping zone. Operating in this manner simplified design problems, and made precise temperature control
of transfer lines unimportant. However, the absence of any liquid phase limited the
trapping mechanism to simple condensation. Highly concentrated or extremely volatile