FAQ About the Headspace Injection Technique
1. When would I use the Headspace Injection Technique?
The headspace injection technique is used to analyze low to trace levels of volatile components in liquids and solids.
In general if the sample is a viscous liquid it is a good candidate for injection with the headspace technique. Examples of this type of sample are cosmetic cream and lotions, elixirs, and used motor oil. It is also a good technique if your liquid sample contains high boiling residuals or insoluble solids, for example, blood alcohol samples, latex paints, inks, adhesives.
Headspace is ideally suited for the analysis of solid samples that are not soluble in any solvent. Examples are contaminated soil and concrete samples, electronic components, adhesive devices and forensic samples. Other solid samples such as flexible packaging films, PVC powders and other polymer blends are routinely analyzed in their solid state by the headspace injection technique.
2. What are the benefits of using the Headspace Injection Technique?
of sample preparation
The headspace injection technique minimizes the need to dissolve solid or dilute liquid samples.
Getting solids into solution can be very time consuming and uses hazardous and expensive solvents.
Dissolving or diluting your sample may introduce volatile impurities into the sample that may interfere with your analysis.
When a headspace vapor sample is injected into the GC it contains only the volatiles components present in your sample. Solids and high boiling liquids remain in the headspace vial and will not contaminate your GC. Capillary columns used with headspace injection can last for years without becoming contaminated.
3. Can the headspace injection technique be used for the accurate and precise quantitative analysis of my sample?
Yes! The headspace injection technique is a rugged and precise quantitative technique. When the headspace method parameters have been properly setup and optimized it can be used routinely for quantitative analysis.
As in all quantitative GC analysis, a known standard that is similar to the actual sample must be prepared. This standard allows the headspace user to calibrate his GC method.
4. Can I remove more then one sample from an equilibrated headspace vial and achieve accurate and precise results?
When performing quantitative headspace GC analysis it is not recommended that more then one injection be made from a vial. This is especially important when the partition coefficient is low, i.e. when a high percentage of the components of interest are in the gas phase (headspace).
An example of that type of headspace sample would be the analysis of benzene, toluene and xylenes (BTX) in water, where almost 100% of these volatile components are in the headspace vapor phase in the sample vial.
5. How can I prevent leaks at the headspace vial crimp seal?
Low results or irreproducible results may be due to leaks at the headspace vial crimp seal. This is usually a result of an improperly adjusted or excessively worn vial seal crimper. An improperly crimped vial seal will leak when the internal pressure increases during thermal equilibrium or during the pressurization step of an automated headspace injection.
Proper hand crimper technique is important. Insert the vial and crimp seal squarely into the jaws of the crimper. Crimp the seal very firmly to the stop on the crimper handles. Turn the vial ¼ of a turn or 90 degrees and recrimp the vial.
If the seal is not well crimped, re-crimp the vial or adjust the crimper tool as necessary. If re-adjustment of the crimper is no longer possible because the crimper is badly worn, replace the crimper with a new one.