ASK BEN | 4 Simple Steps to Find the Right GC Liner
We get a number of questions on GC liners, specifically what liner they should be using for their application. Choosing the appropriate GC inlet liner is crucial to ensure your sample can be properly analyzed. It ensures that the proper amount of sample is transferred onto the GC column without disrupting the sample itself. So, what are the different types of liners, and how do you choose the right one?
"Choosing the appropriate GC inlet liner is crucial to ensure your sample can be properly analyzed. It ensures that the proper amount of sample is transferred onto the GC column without disrupting the sample itself."
GC Basics: Injection Techniques
Before diving into liners, first you should understand the two most common injection techniques for GC. Split vs. splitless is a common conversation in gas chromatography, and the choice really depends on the sample concentration, the detector’s sensitivity, and other method requirements. We can go into more detail another time, but here is a quick summary of how to determine if you should be doing split or splitless injection.
Split injection (most common):
- Used when sample concentrations are not too low
- High flow rates = sharp, narrow peaks and reduced time for adverse interactions
- Ideal for detectors with high sensitivity since most of the sample is vented
Alternatively, in splitless injection:
- You can analyze samples with low concentration of the analyte(s) of interest, or with lower sensitivity detectors as more of the sample ends up on the column
- Lower flow rates can result in wider peaks
- Sometimes degradation can occur through adsorption and breakdown
How Do I Choose an Inlet Liner for Split or Splitless Injection?
Once you’ve determined the type of injection you’ll be doing, you can start to narrow down the options for your GC inlet liner.
- Split or splitless injection? Once you know what type of injection you’ll be doing, you can easily reduce your choices to include only either split or splitless injection liners.
- Establish the ideal internal shape of the liner. Split liners are typically open at the bottom to enable flow to pass across the bottom of the liner, whereas splitless liners are typically tapered at the bottom to funnel the sample onto the column and minimize sample contact with the inlet. Tapered-bottom liners are also helpful for highly active compounds.
- Decide: packed liner, and wool placement. Liners can be packed with wool to help with the vaporization of the sample (by increasing surface area), but unpacked liners are less expensive than packed liners. Packing near the top of the liner can help with solid particles entering the column but could potentially result in carryover from injection to injection.
- Determining the internal diameter of the liner. your liner must accommodate the amount of sample that will be vaporizing in the liner. A smaller diameter leads to narrower peaks but be mindful that the sample can expand enough so your vaporized sample doesn’t expand beyond the liner into the carrier gas/open lines. Most liners come in a variety of internal diameters, so you can choose an appropriate volume.
Liners for Gas Analysis
One additional liner type that you may come across is a completely straight liner with a narrow ID (to eliminate diffusion before the gas hits the column) and no wool. This type of liner is used for samples that are already in the gas phase. This would include headspace analysis, purge-and-trap, or air sampling. These liners are essentially just a mode of transport for the gas, since it doesn’t need to vaporize the sample.
There are a lot of GC inlet liners to choose from, and often times many choices will work for different applications. Start by determining the type of injection you’ll be performing. This will help narrow down your options. Determine what shape, packing, and size liner will be best for your compounds, and you’ll be all set! On a related note, if you haven’t already, consider switching to Parker gas generators for an easy and efficient way to support your GC instruments. Reach out to our support team for more information on properly equipping your GC system.