Why Leak Check Your GC System?

All too often, analysts tell us "I'm sure I don't have any leaks in my GC system." But what tool will allow you to be confident that your analytical

system truly is leak free? We strongly encourage every analyst to incorporate electronic leak detection into their daily routine, to improve analytical performance, minimize troubleshooting, and prevent damage to columns and sensitive detectors.

Think of leak checking as critical preventative maintenance, and good laboratory practice, that you can't afford NOT to do. Keep in mind that leaks can cause significant losses of expensive high quality gas, shortened trap and purifier lifetimes, destroy columns, and increase system and detector maintenance. Furthermore, some detectors, such as ECDs, can be severely damaged by exposure to oxygen through system leaks.

You will avoid many common analytical problems by leak checking. Unlike in HPLC systems where leaks are frequent and (somewhat) more apparent, leaks in GC systems can be subtle and difficult to isolate without proper equipment.

• Begin at the carrier gas source and regulator and carefully check each fitting and connection along the pathway to the GC.

• Turn off the oven fan and check all fittings, adapters, and connections inside the oven as well.

• Don't forget to check all column and guard column connections, such as Press-Tight connectors or unions, as well - often, a leak can be traced to a column end that was crushed during installation or perhaps connected incorrectly.

The best way to leak-check a capillary column system is to use a thermal conductivity leak detector, such as the newest generation Restek Electronic Leak Detector (cat.# 28500). This portable, reliable, and relatively inexpensive handheld device detects minute traces of carrier gas without contaminating the system.

Note that leaks in a GC/mass spectrometer (MS) system can be determined by monitoring for mass 28 (nitrogen) or 32 (oxygen), or by spraying argon gas around fittings and connections and monitoring for mass 40. As an alternative, many mass spec users will simply use air duster cans in place of argon. This product is inexpensive and is readily available.

Note that we strongly recommend that you never use liquid leak detectors that contain soaps or surfactants in capillary chromatography.

Leaks can draw these materials into the system where they may contaminate the column and make high sensitivity operation difficult. In addition, soap-based liquid leak detectors can cause permanent damage to the stationary phase.

If a thermal conductivity leak detector is not available, a pressure decay test can also be used to find major gas leaks. This approach can be particularly helpful in checking long gas supply lines in the laboratory facility. Unfortunately, although the pressure decay can be helpful in identifying the presence of a leak (somewhere?), pinpointing the exact location of the leak is problematic. Yes, there is a leak present – but where is it?

In summary, every GC laboratory should have access to an electronic leak detector and all analysts should be trained to use this tool every time a new column or fitting is installed, a cylinder is changed, or instrument troubleshooting is indicated. To minimize the possibility of damaging your column and detector, NEVER condition a column without leak checking the system first!

Frequent, thorough, and careful leak checking validates the integrity of the entire carrier gas flow path in a GC system and will help you to avoid damaging expensive columns.