11.13 : Gas Chromatography: Sample Injection Systems

In gas chromatography, the sample is introduced as a vapor plug into the carrier gas stream for high efficiency and resolution. A microsyringe injects the sample solution into a heated sample port, vaporizing it and mixing it with the carrier gas. This process is important to ensure the sample is properly prepared for analysis. Thermally sensitive samples can be injected directly into the column and volatilized by slowly increasing the column temperature.

Two primary injection methods are used depending on the sample concentrations: split and splitless injection. The split injection method is used for concentrated samples, as the splitless injection mode is preferred for trace analytes. Capillary columns use split and splitless injection methods to prevent overloading and enable analysis over a wide concentration range. In the split injection method, a split valve allows only a small proportion of the sample, depending on its split ratio, to reach the column. This method helps prevent overloading and improve the lifetime of the column.

On the other hand, in the splitless injection mode, the split valve is closed to permit the maximum amount of sample to reach the column. This method increases sensitivity but can lead to column overload and saturation when using concentrated samples. The choice of injection method depends on the sample concentration and the required sensitivity of the analysis.