Sample preparation is a critical step in Gas Chromatography (GC) because the sample must be clean, volatile, and compatible with the instrument.
Here’s a overview:
1. Choosing the Sample Type
- GC works best with volatile compounds that can be vaporized without decomposing.
- Non-volatile or thermally unstable samples may require derivatization (chemical modification) to make them GC-compatible.
2. Dissolving the Sample
- Liquid samples can be used directly or diluted with a suitable solvent (like hexane or methanol).
- Solid samples may need extraction with a solvent to pull out the analytes.
3. Filtration
- Remove particles or insoluble matter using a syringe filter.
- Prevents clogging of the injector or column.
4. Concentration
- If analytes are in very low amounts, the sample may be concentrated by evaporation.
- Avoid overheating to prevent loss of volatile compounds.
5. Derivatization (if needed)
- Converts polar or non-volatile compounds into more volatile derivatives.
- Example: converting sugars or acids into trimethylsilyl derivatives.
6. Preparing for Injection
- Place the prepared sample in a GC vial.
- Ensure proper volume (usually microliters) for injection.
- For headspace GC, the sample is sealed in a vial, and only the vapor above the sample is injected.
In short:
To prepare a sample for GC:
- Extract or dissolve it.
- Filter or clean it.
- Concentrate or derivatize if needed.
- Place in a vial for injection.
This ensures the sample is pure, volatile, and safe for the GC system.