Headspace Sampling
Equilibrium sampling of volatile compounds occurs in the sealed air space above a solid or liquid sample in a closed vial. For textile testing, static headspace extraction is used to analyze VOCs and residual solvents without needing to dissolve the entire fabric. This method is particularly useful for detecting odours or restricted gases that evaporate easily at moderate temperatures.
Thermal Equilibrium
The vial is placed in a heated oven for a set period to allow the volatile components to move from the textile into the gas phase. Under the conditions of static headspace extraction, the concentration in the air space becomes proportional to the concentration in the sample. Once this balance is reached, a portion of the gas is taken for analysis.
Analytical Advantages
This technique avoids the use of large volumes of liquid solvents and keeps the injection system of the chromatograph clean. Because only the gas is injected, static headspace extraction prevents non-volatile dyes and oils from contaminating the laboratory equipment. It is the preferred method for measuring monomers like vinyl chloride or formaldehyde in plastic components of garments.
The sensitivity can be increased by adjusting the temperature or the salt content of the sample matrix. Precise control of the vial pressure and transfer line temperature is necessary to prevent the loss of analytes before they reach the detector.
Limit of Detection
While effective for highly volatile substances, it is less suitable for chemicals with high boiling points. Standard protocols define the exact heating times and temperatures for each target compound. It provides a non-destructive way to screen for chemical safety.
