GC-Liner: Selecting an appropriate liner

Liners are an indispensable component for the proper functioning of the GC system. They allow a sample which is injected in the liquid state to vaporize into the gaseous phase due to raised temperature at the opening and is then transferred onto the head of the GC column. There is a significant increase in volume during vaporization, hence the liner volume must be sufficient to accomodate the vapor produced. An expansion volume which is greater than the capacity of the liner can lead to sample loss, poor reproducibility, reduced sensitivity and backflash, affecting the entire GC system.

Selecting an appropriate liner

There are several aspects to consider when choosing an appropriate GC liner for a particular application. These include the choice of injection technique and a suitable injection volume for a specific liner volume. It should also be determined in advance whether vaporization accelerators or other chemical additives are used.

It is very important to choose an appropriate liner for your GC system. However, it is often not so easy. The key aspects to consider are as follows.

Regular replacement of the liner

Serious problems may arise if liners are not replaced regularly. A liner that has already been used cannot guarantee consistent reproducibility, which could affect the entire GC system. The liner should be replaced regularly to avoid deterioration of the peak shape and sample loss. Interfering peaks can also be the result of a liner that has not been replaced for a long time.

1. Liner ID and Geometry

Different liner internal diameters (ID) indicate different liner volumes. A number of factors influence or reduce the effective volume of a liner:

• Taper, baffles and other functions of the liner
• Packing material
• Carrier gas

Typically, the vapor cloud formed by the sample should not exceed half the volume capacity of the liner. The volume of expansion of solvents limits the volume of injection. Low density, high molecular weight solvents are preferred as these increase the volume of the solvent that is injected and can reduce detection limits.

2. Injection technique

Another key aspect when choosing an appropriate liner is the injection technique. Split liners allow the split flow to pass across the bottom of the liner, hence removing part of the sample, enabling a split injection to be performed. A selection of split liners can be found here.

Splitless liners are usually tapered at the bottom. This helps to transfer the sample onto the column and minimizes sample contact with reactive metal components in the opening during the injection.

3. Packing material of the iner

Activity in inlet liners may adsorb sample components and cause peak tailing, leading to reduced sensitivity and reproducibility. The packing material needs to provide highly inert pathways to guard against sample adsorption and sample degradation.

4. Deaktivation / Treatment of the liner

You can choose from a large range of liners from numerous manufacturers in the Analytics Shop. These high quality liners offer significantly improved inertness for a wide range of applications. When used in various deactivation techniques, they help to increase transfer of the sample onto the GC column, resulting in increased accuracy and precision in the analysis itself. This enables lower detection limits for some active substances.