Cryogenic modulator

Figure 4.1 Schematic diagram of a coupled column system. The first column (ID) is connected to the second column (2D) tlirough the interface or valve system. The interface can be a diiect coupling, a live T-union, a complex multiport valve, or a thermal or cryogenic modulation system. The stimulus can be the switching of the valve, abalancing pressure to divert flow towards 2D, an added flow that is used in pressure tuning, or the drive mechanism for the modulator. The line to detector 1 will normally be a non-retaining section of column. In a two-oven system, ID and 2D will be in different ovens the dotted line indicates separately heated zones.

Fig. 15.4 A dual-jet cryogenic modulator, a Right-hand-side jet traps analytes eluted from the first column b right-hand-side jet switched off, cold spot heats up rapidly and analyte pulse is released into the second column simultaneously, left-hand-side jet switched on to prevent leakage of first-column material c next modulation cycle is started (adapted from [32])...

Figure 6.5 Schematic diagram of a typical interface used for on-line SFE-GC coupling (from ref. 40) 1, extraction cell 2, restrictor 3, on-column injector 4, heater 5, oven 6, cryogenic module 7, column.

In a technique referred to as GC X GC or two-dimensional GC, direct coupling of two columns with different selectivities allows for a continuous separation of closely eluting or coeluting peaks therefore, it readily separates PAH isomers and many other species that coelute under ordinary capillary column conditions. A GC X GC-MS system has been described where the first separation was on a 20 m X 0.25 mm i.d. 5% phenyl dimethylpolysiloxane column with 0.25 /rm film thickness. Eluate from the first column passed through a cryogenic modulator onto a... 

As an example, in Figure 3A, the inside of the oven of a GCxGC system equipped with a quad-jet dual stage cryogenic modulator is pictured (see later in this chapter for further details on the modulation process using this particular modulator). A GC split-splitless injector is located on the top left side, the column (30 m) is located on the right part, and the end of is visible on the... 

Depending on the modulator used, various connecting setups can be adopted to link the D to the D. In most heated modulators, a piece of uncoated capillary tubing follows a piece of thick film capillary column to ensure phase termination and decrease the retention of analytes before creating the band transferred into the D column. For cryogenic modulators, modulation can take place directly on the D capillary column. For valve-based modulation, the valve sample loop acts as a connection between the two dimensions. In other cases, the modulation process can simply take place at the beginning of the D column. In the early... 

The several different modulators that are commercially available can be classified in two main categories thermal modulators and valve-based modulators. Thermal modulators are the most frequently used and in turn can be broken down into two categories those whose principle involves a temperature increase and, inversely, cryogenic modulators. 

Figure 12 The modulation process in a dual-stage liquid CO2 cryogenic modulator.

---