What are the best sampling techniques for the analysis of VOCs and SVOCs in air using thermal desorption?
Presented at CEM India - Sampling techniques, 2024
Thermal desorbers were originally developed to detect relatively low-boiling volatile organic compounds (VOCs) in ambient air, but have since expanded their capabilities, with modern TD instruments able to monitor up to C44.
Despite this universality of TD, there is no single sampling technique for ambient air monitoring that provides optimum performance across the required range of analytes and sample concentrations. In many cases, the choice of sampling method is defined by precedent and/or the need to adhere to certain standard methods. However, as limit levels are reduced and target analyte ranges expand, it is worth re-assessing the best sampling technique in the light of the capabilities of modern analytical systems.
TD fundamentally involves the collection of vapours onto a bed of sorbent material(s), followed by desorption of these vapours, in order to concentrate them into a smaller volume of gas. With tube-based sampling, this process is carried out twice, once on the sorbent tube (at ambient temperature) and then on the focusing trap (at below-ambient temperature), while ‘whole-air’ sampling involves just the focusing-trap step.
