Headspace sampling is a method used in gas chromatography to separate analytes in liquids and solids from complex matrices. The GC analysis is made cleaner by stopping any compounds of low volatility from entering the GC column. When compared to other extraction methods headspace sampling is more time and resource efficient.
Headspace sampling finds applications in testing for the presence of solvents in pharmaceutical packaging, blood screening for toxins and illicit substances, the analysis of gases in oils, environmental analysis of VOCs and determining aroma components in food and beverage manufacturing.
To carry out a headspace analysis, the sample of interest along with a dilution solvent and the headspace (a gas above the sample), are placed into a chromatographic sample holder. The vial is then heated to establish an equilibrium between the analyte in the sample and in the headspace. Following the establishment of the equilibrium the vial is pressurized by a carrier gas injection.
Once the vial has been pressurized the headspace gas and carrier gas are introduced to the GC inlet then through the column and oven for analysis.
Conventionally helium has been the most popular choice of carrier gas for headspace GC due to its high inertness. However, as helium stocks are depleted the price of the gas has increased significantly, leading to many researchers running headspace GC with different carrier gases.
Both nitrogen and hydrogen gas have been demonstrated to function to a high ability as helium with both gases being highly available and inexpensive. Hydrogen is the best choice of gas because it is not as slow moving as nitrogen, it is more available (and therefore cheaper) and there is a lower risk of cross-reactions occurring between the gas and analyte. In addition, hydrogen is the fastest inert gas for GC analysis of analytes.
Ordering gas cylinders and receiving them by delivery is more expensive than on-site generation and storage of the cylinders can present safety hazards. Proton OnSite is an established provider of on-site hydrogen generators which can provide researchers with a safer and more economical method of hydrogen delivery – on-site generation via PEM electrolysis.
On-site hydrogen generation provides researchers with more flexibility, allowing them to generate hydrogen as and when it is needed, and without the need to take up space with hydrogen cylinders. On-site generation means the gas needed for headspace GC is always available and at the high purity that the technique requires. Proton OnSite’s systems are capable of producing hydrogen at a purity of up to 99.9995%.
This information has been sourced, reviewed and adapted from materials provided by Proton OnSite.
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