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Both the USEPA and the Agency for Toxic Substances agree that the risk of breathing indoor levels of chlordane/heptachlor or aldrin/dieldrin begin at 5 nanogram per cubic meter (5 ng/M3) of air. The method you select should be able to detect these insecticides at this level.
Beware of procedures that uses air conditioning filters. This method is very insensitive and can not provide an air concentration. Other methods – polyurethane form (PUF) or solid sorbents – that require a solvent extraction step may be insensitive and prone to the loss of these semi-volatile during the sample concentration (solvent blow-down) step.
The method use by ToxFree increases sensitivity and accuracy by thermally desorbing the insecticides collected on the solid sorbent directly into the capillary column of the gas chromatograph.