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What is the basic principles of headspace sampling and the factors that affect experimental results?
Date: 2022-09-09

The basic of Headspace Sampling for GC analysis

Headspace sampling is a sample analysis technique used in gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). For headspace analysis techniques, the gas in the headspace above the sample in the gas layer or vial is analyzed instead of taking a sample directly from the sample. Headspace analysis requires that the target compound is highly volatile, while the rest of the sample is not. Headspace analysis is ideal as an alternative to labor-intensive extractions, for example, when sample types are solids, viscous liquids, blood, or pharmaceuticals.
headspace sampling analysis

Headspace sampling process

Transfer samples to appropriate headspace vials for headspace analysis and cap immediately to minimize loss of volatile components. The headspace vial containing the sample is sealed and heated in a constant temperature oven; this step is to allow the low boiling point to evaporate quickly and begin to migrate between the sample and the headspace, eventually reaching equilibrium. The time to perform the equilibration depends on the nature of the sample compounds. Reduce experiment time by heating headspace flasks in an oven or other temperature-controlled environment. Once equilibrium is established, the sampling process can begin.

Headspace vials are typically 2mL larger than the liquid sample being analyzed. Common headspace vials capacity are 10ml and 20ml. The headspace vial is round finished, Screw top and crimp top mouth. Large volume vials can accommodate larger sample volumes and/or larger sample headspace. Since headspace analysis is best suited for volatile compounds, the use of high-quality headspace vials and caps septa to form an airtight seal is critical to the results of the experiment.
GC headspace analysis

     • The temperature-controlled oven provides a constant temperature so that the volatiles in the headspace vials are balanced before the GC run begins.
     •The sampling probe pierces the vials and allows two things to happen inside the vials: 1) gas is added to increase the vial pressure, and 2) the sample is transferred from the vial to the headspace loop.
     •The heated injection ring contains a fixed volume of sample that can be repeated.
     •The heating transfer line creates a thermal control channel that transfers the sample contents from the headspace injector to the GC for analysis.

Benefits of GC Headspace analysis

•Compatible with virtually any matrix. Low demand on the sample capacity to be measured;
•The sample itself does not have to be volatile, Wide range of applications in GC;
•Little or no sample preparation, Reduce sample preparation errors;
•Smaller solvent peak. The solvent peak area is small and the target analyte is less affected.
•Clean samples reduce contamination of GC inlets, columns, detectors, or mass spectrometer sources, reducing maintenance costs.
•Often higher sensitivity with good precision and linearity.

Factors influencing the results of the headspace experiment

The results of the headspace analysis are affected by many factors, such as the quality of the headspace vial, the quality of the caps and septums, the air load, etc. In the experimental description above, we can see that the headspace vials are heated after loading. In this link, the heat resistance of the headspace vial is first examined, because some vials will explode directly during the heating process. In addition, whether the gasket releases impurities during the heating process also has an important impact on the experimental results.

In summary, the headspace vials kit is not as expensive as the analytical instrument in terms of price, but the impact on the results of the experiment is crucial. The headspace bottle provided by Aijiren has been well received by laboratory analysts. And Aijiren's head empty bottle can be fully compatible with Agilent, Varian, Shimadzu and other instruments. In view of the characteristics of the large air pressure inside the empty bottle of the head, Aijiren has developed an aluminum cap that can relieve pressure. As long as you are looking for an empty bottle at the top, Aijiren is the only option.