FAQ >> FAQ Solvents for GC HeadSpace
FAQ Solvents for GC HeadSpace
- It depends on the type of sample and analysis required, but if the sample with the analytes of interest is equally soluble and stable in both dissolution media, it is preferable to use DMSO over DMF, as the latter is more volatile and toxic. In addition the boiling point of DMSO is higher (bp = 189 °C) than DMF (bp = 153 °C), which extends the linear range of interest in the chromatogram.
- As the Headspace technique requires pressurization of the vial for sampling, and environmental pressure varies each day, the retention times are affected and may even vary by up to 0.2 min. Therefore, a standard mixture with all analytes of interest must be injected after each sample analysis.
You can increase the sensitivity by changing these two parameters:
- thermostatization temperature
- sample volume
in the case of very soluble compounds in the dissolution medium, only the temperature will increase the sensitivity, but for poorly soluble compounds dissolved in the solvent, increasing the sample volume will decrease the volume of the gas phase which will increase sensitivity.
Therefore these two parameters must be well controlled.
We can also increase the sensitivity by varying the analysis medium:
1. Adding a small percentage of water-based solvent can cause than residual more nonpolar solvents in the presence of a more polar médium, tends to evaporate and therefore concentrate more in the gas phase, increasing sensitivity.
2. In the event of the dissolution medium is water, all those residual water soluble solvents tend not to evaporate, and therefore to increase sensitivity the temperature must be increased, another possibility is to add salt to the water making the more residual solvents more insoluble in it, and this encourages them to evaporate and move into the head space.
- Yes. The matrix in which the analytes of interest are dissolved affects the signal. Different solvent solution, different signal.
- Working with Multiextraction mode (a single thermostated sample is injected "n" times until total extraction of the analyte of interest is completed) or Purge and Trap technique (where the analyte is extracted and completely swept away by an inert gas, isolating it from the matrix).