Page 94 - Multidimensional Chromatography

86 Multidimensional Chromatography

for headspace or thermal desorption experiments and, by extension, to solid-phase
microextraction sample introduction, where the ability to focus the band at the head
of the column is advantageous. When the LMCS is positioned between two columns
in which we wish to perform some separation function, a range of multidimensional
methods, some of which are novel approaches to solute manipulation, can be
achieved (21). Figure 4.6 illustrates the mode where two separation columns are
interfaced through the cryomodulator unit. Note that the capillary column is fed
through the cryotrap, and so the solute is retained within the column (sorbed in or on
the stationary phase on the walls of the column) which is surrounded by the cooled
device.

4.3.3 MODES OF THE LMCS USING COUPLED
SEPARATION COLUMNS

Once solute has been focused in space within the cryotrap, they are subsequently
ejected out of the cold region (we can refer to this as being like a re-injection into the

Figure 4.6 The LMCS system incorporates a moveable cryogenic trap T through which the
capillary column is passed. The modulator (M) can be a pneumatic or motor driven device that
moves T up and down as required, according to either preselected times (for a selective mode)
or at a fast constant period for GC GC.