4. Conclusion
Silica monolithic capillary columns can be easily used for gas analysis using high pressure injection valve and pressure regulators allowing sample injection at high pressure of carrier gas (up to 60 bar). Characterization of multiple silica monolithic capillary columns has confirmed the good repeatability and reproducibility for intra-batch and inter-batch columns. Then, to understand the hydrodynamic flow and retention on monolithic columns, a special attention was required due to the temperature difference between the oven area and the FID detector which contain a significant length of the column when short columns (less than 30 cm) were used. Nitrogen or carbon dioxide used as carrier gas has a strong effect on efficiency, retention and selectivity. Indeed, due to carrier gas interaction with some active surface sites, the retention time is reduced and furthermore the selectivity can be modified inrelation to different types of site on the silica surface. Higher is the pressure of the carrier gas, or lower is the temperature, higher is the adsorption of the carrier gas on active sites and lower is the retention. Finally, the lowest Hmin values were obtained with carbondioxide, followed by nitrogen and helium.
The high pressure used to perform analysis on silica monolithic columns could also be profitable for industrial applications. Indeed, as industrial processes often work with high sample pressure, and so sample line could be connected directly to the injection valveon a HPGC set up without any need of pressure reduction during sampling.