Liner Volume
The purpose of the injection port is to allow the introduction of a sample into the gas chromatograph in an accurate, reproducible manner. The vaporized sample should be a true representation of the liquid sample and, unless specifically desired, should be injected without chemical change. The elevated temperatures used in the inlet vaporize the liquid sample to a gas for transfer to the head of the column. This phase transition is accompanied by a very significant volume change. The volume of the resulting vapor must be small enough to fit within the volume of the liner. If the volume is too great for the liner, reproducibility and sensitivity can be compromised, due to backflash and loss of the sample into the septum purge or split lines. Backflash also frequently results in sample carryover.
Larger volume liners (> 800 µL) are characterized by larger inside diameters (ID) and are typically used with injection sizes of 1 µL or more. The small volume liners have a smaller ID and are usually used with small injection sizes (< 1 µL), fast µm ID columns, gas samples, or when using external sampling devices like headspace and purge and trap.
Liner Deactivation
Active sites on inlet liners can adsorb sample components and cause peak tailing, with potential loss of sensitivity and reproducibility. Deactivation agents are used to cover or react with active sites on the glass surface of the liner. Agilent liners are deactivated using deactivation procedures that produce reproducible and inert liners, with long lifetimes. For splitless applications or when even slightly polar compounds must be analyzed, a deactivated liner should be used.
With use, even deactivated liners can begin to exhibit activity. When this occurs, the liner should be replaced. Liners can be cleaned to remove particulate material or solvent rinsed to remove less volatile components. However, choosing the proper liner cleaning procedure can be difficult. Some solvents may remove the deactivation layer or tools might scratch the glass surface of the liner, resulting in the generation of unwanted active sites.
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