How are the VOCs collected and measured in the air monitoring tubes?
Initially, an accredited laboratory are contacted to advise upon the analysis technique based upon available site information. The laboratory then prepares and sends out the diffusion tubes for placement. VOCs are collected on special adsorption tubes which contain a media to which contaminants adhere. Two methods of diffusion tube analysis have been applied to the Hauxton monitoring regime: • Active sampling – air is actively pumped into the diffusion tube. This monitoring is carried out over a 24-hour period. • Passive sampling – air passes diffusively into the tube. This monitoring is carried out over a 28-day period. The tubes are exposed to the air for the required period to allow the air to enter the tubes and the contaminants to adhere to the media. At the end of the monitoring period, the diffusion tubes are sealed and sent to the laboratory for analysis by Gas Chromatography Mass Spectrometry (GC-MS). Once at the laboratory the contaminants are driven off the media by heating
