Page 92 - Multidimensional Chromatography

84 Multidimensional Chromatography

Figure 4.4 The slotted heater (see Figure 4.3) is held at its rest position 1 until it is moved to
sweep across the accumulator column, as shown at position 2. When arriving at position 3, it
rests again over the exit connection C2 to ensure solute is fully delivered to column 2. Then it
rotates back to position 1, awaiting the next repetition of modulation.

4.3.2 LONGITUDINAL CRYOGENIC MODULATION
The cryogenic modulator (termed a longitudinally modulated cryogenic system
(LMCS)), which was developed at The Royal Melbourne Institute of Technology,
has a number of diverse applications mainly due to the universal value of cryogenic
methods in GC, one of which is the comprehensive GC GC technique. It offers
some unique ways to manipulate chromatographic bands (17), which allows certain
novel chromatographic results to be obtained. The LMCS uses a small cryogenic
trap as a hollow sleeve about the capillary column to cool, and hence trap, any solute
that enters the cold region (18). The key to this method is that the trap is moved
along the capillary column to expose any trapped solute to the heat of the oven,
which rapidly allows the solute to heat up and pass to 2D. Simply allowing the trap
to heat up by turning off the CO 2 supply is not suitable (19); however, we have
found that supplementary heating is also not required, with the prevailing heat of the
oven being adequate to heat up the cold region of the column once the trap is slid
away from the trapping region. Such a trap can perform a number of functions that
conventional cryotraps are routinely used for. It is located inside the oven, and is
used to cool a small length of fused silica column. Thus, it can focus volatile com-
pounds at the injection end of the column system, or it can be used at the outlet end
of the column inside the oven (just before the detector). These options are shown in
Figure 4.5. The results of a definitive study of injection and detection applications of
the LMCS have been reported (20), which suggest that the system should be useful