Leak Checking a 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, increased column bleed, and increased system and detector maintenance. Furthermore, some detectors, such as ECDs, can be severely damaged by exposure to oxygen through system leaks.

You can avoid or minimize many problems by leak checking the complete analytical system, not just the chromatograph, during the plumbing process and periodically thereafter. Unlike in HPLC systems, where leaks are apparent, leaks in GC systems can be subtle and difficult to isolate without proper equipment. Therefore, we recommend leak checking the system before beginning the column conditioning cycle and eliminating all leaks before proceeding with column conditioning and analytical work.

• 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, adaptors, and connections inside the oven as well.
• Don't forget to check all column and guard column connections, such as connectors or unions as well—often a leak can be traced to a column end that was crushed during installation.

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

Note that we strongly recommend you never use liquid leak detectors that contain soaps or surfactants in capillary chromatography. Leaks draw these materials into the system (via the Venturi effect), where they contaminate the column, making high sensitivity operation difficult. In addition, liquid leak detectors can cause permanent damage to the stationary phase.

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! Remember: a leak-free system will allow greater sample throughput and less downtime in the long run!