Another early method (closely related to the modern purge-and-trap procedure) involved passing a stream of gas through a water sample to release the volatiles, which were again collected on a sorbent-packed tube.
[5] Such axial-type samplers, which later became known as 'sorbent tubes', were laid out as an industry standard in the late 1970s, by Working Group 5 (WG5) of the UK Health & Safety's Committee on Analytical Requirements (HSE CAR).
Heating this trap releases the analytes once again, but this time in an even smaller volume of gas (typically 100–200 μL), resulting in improved sensitivity and better GC peak shape.
The greater sensitivity of this method has made it increasingly popular for sampling dilute gas streams, or in exploratory work where the target atmosphere is unknown.
Incompatible compounds include: Applications of thermal desorption were originally restricted to occupational health monitoring, but have since extended to cover a much wider range.
Some of the most important are mentioned below – where available, examples of early reports, and more recent citations (including those of widely used standard methods) have been given: