GC Inlet Liner Selection Tips

GC Performance Tip, Reporter Vol. 29.2

An injection port liner is used to make the connection between sample introduction and the GC column. Four primary injection techniques are used in GC; split, splitless, direct, and on-column. Inlet liners should be selected based on the injection technique being used to ensure optimal sample transfer to the column.

Split Injection: The most common injection method used. Split liners use a design that establishes turbulent flow rather than laminar flow, ensuring sample vaporization and enhancing proper mixing prior to the point where the sample is split, thereby minimizing inlet discrimination. Cups, baffles, twists, or frits are used to facilitate sample mixing. Wool may be used to improve vaporization, and/or to keep non-volatile material from entering the column. Wide bore 2 - 4 mm I.D. inlet liners are necessary for solvent expansion.

Splitless Injection: Because the sample dwell time in the liner is significantly longer in the splitless injection mode, the liner design does not need to create high turbulence. Splitless liners usually are straight 2 - 4 mm I.D. tubes with internal volume between 0.25 and 1 mL (choose a liner with an internal volume equal to or larger than the expansion volume of the solvent). Tapers (either at the bottom, or at both the top and bottom) may be incorporated to help focus analytes onto the column. Wool may be used to improve vaporization, and/or to keep non-volatile material from entering the column.
NOTE: Deactivation of splitless liners is very important due to the long residence time of the sample.

Direct Injection: Often used for gas phase samples, such as with headspace, purge-and-trap, and solid phase microextraction (SPME) techniques, where the entire gas sample is transferred to the column. Because there is no solvent, large internal volumes are not necessary for solvent expansion. Narrow bore 0.5 - 1.5 mm I.D. inlet liners are used to maintain a high linear velocity through the injection port, minimizing band broadening. Also known as flash vaporization.

On-Column Injection: Liquid samples are deposited directly into the inlet of a capillary column. A specialized syringe is usually required. These liners are designed with a tapered region where the column end is seated to create a seal between the column and the liner. This taper also guides the needle into the column. The oven temperature program is then used to vaporize the sample component.

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