4.3.2 Other Inlet Techniques

We use other techniques to introduce the sample to the GC as needed. These include on-column injection, headspace analysis and purge and trap.

1. On-Column Injection: This technique allows deposition of material directly on the column (the basic techiques have the sample injected into the inlet volume and swept onto the colum by carrier gas). Cold on-column injection is a subset of this technique that utilizes a room temperature or colder inlet and is therefore a good technique for thermally labile samples. The column and inlet are slowly ramped to gently vaporize the sample. This makes the GC usable for many compounds that thermally decompose with the flash vaporization of the basic techniques, including samples once thought not suitable for GC analysis.
2. Headspace Analysis: A method used to analyze samples for volatile components is to sample the vapor above the solid (or liquid) with a relative large volume syringe. The sample is placed in a closed container and is often heated (gently, compared to the inlet temperature). For example, this is the technique we use to analyze fire debris samples.
3. Purge and Trap: Another method to analyze for volatiles is purge and trap. In this method, a purge gas is swept over (or through) the sample and is passed through an adsorbate such as charcoal. The adsorbate traps the volatile components entrained in the purge gas. The adsorbate is gently heated to release the trapped components directly into the GC.