Gas Chromatography: Sample Injection Systems

Usually, a microsyringe injects the sample into the gas chromatograph system. 

In the heated sample port, the sample is completely vaporized and mixed with the carrier gas.

In capillary columns, the split and splitless injection methods prevent overloading and enable analysis over a wide concentration range.

The split injection method is used for concentrated samples, where a split valve allows only a small proportion of the sample, depending on its split ratio, to reach the column.

The splitless injection mode is preferred for trace analytes. In this mode, the split valve is closed to permit the maximum amount of sample to reach the column.

Initially, at low column temperatures, the solutes are trapped in a narrow band of condensed solvent at the top of the column. Upon increasing the temperature, separation commences.

If the sample is thermally sensitive, it is injected directly into the column and volatilized by slowly increasing the column temperature.