Headspace Sampler

 

Headspace samplers are a highly versatile analytical tool that allow you to introduce volatile compounds automatically, from virtually any sample matrix, directly into your gas chromatograph or GC/MS instrument. This is a relatively simple technique that maintains a cleaner environment on your instrument than liquid injection techniques, such as purge and trap.

Historically, the headspace method has existed since the late 1950s [12]. The technique involves placing a sample in a vial and heating it to achieve equilibrium. Once the analyte is in thermodynamic equilibrium, an aliquot of the sample vapour is removed from the vial and transferred to a GC for analysis.

There are many variations of this procedure. The simplest is the static headspace extraction, which involves the use of a thermostat to heat a bottle-shaped vial that contains the sample and a rubber septum cap. Once equilibration has been achieved, an aliquot of the sample vapour from the vial is removed with a gas-tight syringe and is introduced into the GC for separation.

Another standard method is dynamic headspace sampling, which is based on the principle of "purging and trapping" the analyte into an adsorptive trap. After a certain amount of time passes, the trap is heated to desorb the trapped volatiles onto the GC column for analysis.

Dynamic headspace sampling is a highly accurate, fast, and inexpensive method for testing for VOCs in water or soil. It is a great way to quickly support waste-site remediation, emergency response, or testing for worker exposure in manufacturing facilities.

The technique is also commonly used to screen for flavor and aroma attributes in raw materials and brewing, as well as for determining when a beverage is complete. The sensitivity of this technique makes it a valuable tool for these applications.

Variations in sample Headspace sampler equilibration are important, but these can be minimized by using temperature-relieving septum caps on your sample vials. Temperatures must be matched to the solubility of the analytes, as higher temperatures will lower their partition coefficient, a factor that determines how much they move into the headspace.

Other headspace parameters, such as vial shaking and sample loop volume, can help to improve the consistency of your results. Taking the time to experiment with these settings, as well as with other headspace methods and techniques that may be available, can improve your lab's overall performance.

For example, it has been shown that the concentration of toluene in nail polish can be reduced by adding simple water to the nail polish sample. This is because toluene dissolves in water, whereas acetates do not. However, this can lead to problems with the analytes being masked by acetates in the nail polish sample.

This can have a significant impact on the analyte's detection limits, particularly for analytes that are very soluble in water. It is important to pay attention to these changes, as large changes can have a detrimental impact on the quality of your results.