Cool on-column inlet

F. David, L. Vanderroost and P. Sandra, Analysis of Polymer Additives Using the HP5890 Series 11, Cool on Column Inlet with Electronic Pressure Control, Hewlett Packard Application Note No. 228-149,1991. 

The cool on-column inlet may be used for all types of analyses, but it excels for analytes that are high-boiling, thermally labile, or otherwise reactive in the inlet. Cool on-column is often used as a control when optimizing other techniques, as it does not suffer from discrimination. Analytical sensitivity is usually very... 

FIGURE 9.11 Schematic of cool on-column inlet. The analytical column or retention gap extends through to the top of the inlet and sample is deposited directly into the column. A duckbill valve or a thin septum may be used with either manual injection... 

For capillary GC, the split/splitless inlet is by far the most common and provides an excellent injection device for most routine applications. For specialized applications, there are several additional inlets available. These include programmed temperature vaporization (PTV) cool on-column and, for packed columns, direct injection. PTV is essentially a split/splitless inlet that has low thermal mass and a heater allowing rapid heating and cooling. Cool injection, which can be performed in both split and splitless mode with the PTV inlet, reduces the possibility of sample degradation in the inlet. Capabilities of the commonly available inlets are summarized in Table 14.3. 

Gas chromatograph systems are composed of an inlet, carrier gas, a column within an oven, and a detector (O Figure 1-1). The inlet should assure that a representative sample reproducibly, and frequently automatically, reaches the column. This chapter will cover injection techniques appropriate for capillary columns. These include direct, split/splitless, programmed temperature vaporization, and cool on-column injection (Dybowski and Kaiser, 2002). 

Gas chromatograph (e.g., Model HP 6890, Hewlett Packard) fitted with a flame ionization detector and a dedicated cool on-column capillary inlet BPX-70 open tubular fused silica column (25 m long, 0.33 i.d., and 0.25-p.m film thickness SGE Chromatography Products)... 

Figure 3.8 Alternative designs for cold on-column injectors, h, Injector with a duck bill valve (Hewlett-Packard), B, an injector with provision for secondary cooling of the column inlet (Carlo-Erba), and C, a temperature- programmable on-column injector with its own oven isolated from the column oven (Varian Associates).

Cold on-column injections allow the inlet and/or inlet section of the column to be cooled or maintained at lower temperatures than the oven. Cold on-column injection suffers from the possibility of sample zone band broading due to excessive solvent flooding. The advantage of cold on-column injection is that it reduces sample discrimination or sample loss, due to syringe needle heating during injection. 

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