GC Inlet Supplies and Maintenance for Optimum Performance

Inlet Liners

In gas chromatography, the inlet is the first part of the instrument that your sample comes in contact with. Using the right liner will aid in sample vaporization; promote efficient, loss-free analyte transfer; and protect your column from contamination—so choosing the correct GC inlet liner is critical for ensuring accurate and precise data. Liners differ in geometric configuration/design, volume, base material, deactivation, and packing. But, choosing the right liner can be greatly simplified by looking at the type of injection. Variations in sample and method may necessitate a different liner, but the following are great initial selections for any analysis:

• Split injection: Topaz Precision split liner with wool
• Splitless injection: Topaz single taper liner with wool
• Direct injection:

• • For semivolatiles or compounds that could be affected by a tailing solvent peak: Topaz Uniliner liner with the hole drilled near the bottom
  • For aqueous injections or compounds that elute away from the solvent peak: Topaz Uniliner liner with the hole drilled near the top

• Gas samples via sample loop injection: Topaz straight liner with a 1.0 mm ID
• PTV injection: Instrument-specific Topaz liner with a small inner diameter and at least one baffle or dimple

For more information about liner selection, visit www.restek.com/liner-choice

Septa

Choosing the right septum for your inlet is even easier. Restek offers several options that are designed to avoid septum bleed and coring, which can damage your column and your data:

• For temperatures up to 350 °C*: Thermolite Plus Septa
• For temperatures up to 400 °C*: Premium Non-Stick BTO Septa
• When coring is an issue (can create unwanted activity):

• • Thermolite Plus or Premium Non-Stick BTO Septa with CenterGuide dimple
  • Merlin Microseal Septa

For more information choosing the right septum for your analysis, visit www.restek.com/septum-choice.

*For 17 mm inlets, the maximum temperature for Thermolite Plus septa is 300 °C and the maximum temperature for BTO septa is 330 °C. For all injectors, minimum recommended operating temperature for BTO septa is 250 °C.

Inlet Seals

Choosing the right inlet seal is more a matter of convenience and preference than data integrity.

As a general rule, especially for sensitive or splitless analyses, you want to avoid bare stainless steel and, instead, use highly inert gold-plated seals to reduce breakdown and adsorption of active compounds.

Restek offers several models of gold-plated inlet seals with washerless installation, including the customer favorite Dual Vespel Ring inlet seal. Its patented design features two soft Vespel rings—embedded in both the top and bottom surfaces—to help ensure a low-torque, leak-tight seal, even after repeated temperature cycles.

Only after you have confirmed that you are using the right GC inlet supplies is it time to think about GC inlet maintenance. Even within a single industry there are simply too many variables in samples, injection techniques, instruments, detectors, etc., to be able to recommend a single general schedule to all analysts for replacing all liners, septa, and inlet seals. Your GC inlet maintenance schedule could be twice a day if you are running dirty samples, or once a year if you are using headspace GC. You need to determine your preventative maintenance (PM) schedule on an analysis-by-analysis basis.

When establishing a PM schedule specific to an analysis, the key term is “preventative.” You are trying to prevent unwanted downtime by replacing your inlet supplies before you have a problem. This way, you can plan for the downtime and choose a time that is not disruptive to your lab. You can also avoid lengthy troubleshooting sessions and missed deadlines.

Simply keep track of how long it generally takes after maintenance to begin seeing data problems commonly associated with the inlet, and then schedule your PM for that analysis and instrument to occur before data problems tend to arise.

Common data problems that can alert you to the need for GC inlet maintenance are:

• • Inlet activity
    • Analyte breakdown creating new compounds (extra peaks)
  • Distorted signal / deteriorating peak shape (e.g., peak tailing)
    • Inlet activity
    • Inlet leaks (e.g., seals around septa, O-rings, ferrules, etc.)

Leak-Free is the Way to Be

A high-quality leak detector—like the Restek Electronic Leak Detector—is a must for every GC lab. Every time you install a new column or perform GC inlet maintenance, be sure to leak-check your GC system before you condition or run an analysis. Minimizing the chances of damaging your column or detector will be well worth the time.

Peak Performance Ensured by Proper GC Inlet Supplies, Maintained Properly

Choosing the right GC inlet supplies—Restek Topaz liners, septa, inlet seals—and implementing a rigorous and timely preventative GC inlet maintenance schedule can help ensure optimum performance, maximum reproducibility, and minimized downtime for your lab.

The Restek inlet supplies you need to get you started can be found here or at www.restek.com/GCacc