Choosing a Liner for Semivolatiles Analyses

By Robert Freeman, Environmental Innovations Chemist

If you are performing split injections, we strongly recommend using a liner containing wool packing. The additional heated surface area from the wool is critical to minimizing the high molecular weight discrimination against late eluting compounds (such as the polynuclear aromatic hydrocarbons) caused by the high flow rates and short sample residence times in split injection. The wool also helps minimize contamination from dirty samples that otherwise would be transferred to the column [1].

Splitless or pulsed splitless injections are common in semivolatiles analysis as labs attempt to decrease detection limits by maximizing sample transfer to the GC column. For splitless injections we recommend a splitless single or double gooseneck liner [2]. The single gooseneck constriction will help reduce the contact of potentially reactive analytes (e.g. hexachlorocyclopentadiene and pyridine) with the hot metal components at the base of the injection port. The additional constriction in a double gooseneck liner will help isolate the sample from the upper portion of the inlet and minimize backflash. Wool packing in the liner will again aid in trapping nonvolatile contaminants before they can reach the GC column.

A direct injection liner also is an option, provided the samples are relatively clean and free of difficult matrices [3]. These liners interface directly to the column by way of a press fit connection. Direct injection liners, like a Uniliner, allow near complete transfer of sample onto the column while eliminating injection port discrimination and analyte interaction with the heated metal components of the inlet. In electronic pressure controlled GC systems a Drilled Uniliner is necessary as the hole in the liner allows flow to be detected by the downstream pressure sensor. Without the hole the GC will go into a safety shutdown because of too much back pressure in the injection port. The hole allows enough pressure to be released from inside the liner and injection port to prevent the EPC shutdown from occurring.

The Drilled Uniliner

To reduce the effects of surface activity in the injection port liner, and focus on the effects of the column on active analytes, we used a Drilled Uniliner inlet liner for this work. This liner connects directly to the column, eliminating contact between the active compounds and active metal surfaces in the injector, and ensuring an inactive sample pathway for analyte transfer from the injection port to the column.

References

[1] Stidsen, G., Fast GC/MS Analysis of Semivolatile Organic Compounds Restek Advantage 2005.01 (2005) 14, 19.
[2] May, K. and C. English, Fast Analysis of Semivolatile Organics Restek Advantage 2004.02 (2004) 2-3, 5.
[3] Freeman, R., Low Level GC/MS for Semivolatiles in Drinking Water Restek Advantage 2006.03 (2006) 12-13.