Basic Principles of Headspace Analysis
A headspace sample is normally prepared in a vial containing the sample, the dilution solvent, a matrix modifier and the headspace. Volatile components from complex sample mixtures can be extracted from non-volatile sample components and isolated in the headspace or gas portion of a sample vial. A sample of the gas in the headspace is injected into a GC system for separation of all of the volatile components.
Phases of the Headspace Vial
G = the gas phase (headspace)
The gas phase is commonly referred to as the headspace and lies above the condensed sample phase.
S = the sample phase
The sample phase contains the compound(s) of interest. It is usually in the form of a liquid or solid in combination with a dilution solvent or a matrix modifier.
Once the sample phase is introduced into the vial and the vial is sealed, volatile components diffuse into the gas phase until the headspace has reached a state of equilibrium as depicted by the arrows. The sample is then taken from the headspace.
From USP <467>
| Headspace Operating Parameters Sets | |||
| | 1 | 2 | 3 |
| Equilibration Temp (oC) | 80 | 105 | 80 |
| Equilibration Time ( Min) | 60 | 45 | 45 |
| Transfer-line Temp (oC) | 85 | 110 | 105 |
| Carrier Gas: N2, He @ appropriate pressure | |||
| Pressurization Time ( s) | 30 | 30 | 30 |
| Injection Volume ( ml) | 1 | 1 | 1 |
