GC injection ports are used to desorb trapped volatiles from the sample (solvent, surface, or adsorbent matrix) and channel sample volatiles into the column. Injectors differ in their temperature profiles and the proportion of sample volatiles directed to the column head.
The following tips should serve as a guide when deciding on what kind of analysis and injector type to use.
- For solvent desorption methods, the injection port temperature should be at least 10°C warmer than the maximum oven temperature used in the analysis. For thermal desorption methods such as SPME or Tenax, a slightly cooler injector temperature of 200°C or less is sufficient to desorb all of the absorbed volatiles.
- The injection split refers to the proportion of the volatilized sample channelled onto the column. To maximize the amount of material injected on the column, use splitless injection.
- Purge the injector at 1 minute to keep additional less volatile compounds from loading onto the column and degrading the column chromatography.
- For thermal desorption methods such as Tenax TA, a modified injector improves the chromatography. By contrast, SPME thermal desorption and solvent desorption methods use an unmodified injection inlet with a special inner glass liner.
- A serious drawback of most GC methods is that the extremely high temperatures commonly used in injector ports can thermally degrade unstable compounds. Destruction of these thermolabile compounds can be minimized through the use of Cool-on-column (COC) injector ports that allow sample volatiles to enter the column at low injector temperatures before the system is heated up.