Let's Talk Headspace Sampling
Headspace sampling is a technique used in gas chromatography in which compounds of interest in liquids and solids are extracted from their complex matrices. Headspace sampling prevents non-volatile substances from entering the inlet and column in order to simplify the analysis. It is commonly used in extracting volatile organic compounds (VOC) from wastewater and contaminated land samples, residual solvents in packaging and pharmaceuticals, blood alcohol and toxicology screenings, aroma components from food and beverages, and diagnostic gas analysis from oils. Headspace sampling is much quicker and less expensive in comparison to other extraction techniques.
In a headspace analysis, the sample is put into a chromatographic vial which includes the sample, the dilution solvent, and the headspace. The headspace is the gas space above the sample in the vial. The sample is heated for a period of time in order to create equilibrium of the desired compound in the headspace. The carrier gas is injected into the headspace to pressurize the vial. From there, only the gas in the headspace is injected into the GC with the carrier gas and taken through the inlet into column and regulated oven, where the samples will be tested and analyzed.
Helium has always been the number one carrier gas used for headspace gas chromatography, but as helium prices go up and its availability go down, chromatographers are switching to using other gases as their carrier gas. Hydrogen and nitrogen have proven to work just as effectively as a carrier gas in gas chromatography. They are both less expensive and more available. However, nitrogen is very slow moving. Some of the benefits of choosing hydrogen over helium include cheaper prices, availability, and it doesn’t react with the compounds of interest. Hydrogen is also the fastest gas when it comes to getting a proper analysis of a specific compound.
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