A new system of refillable and uniquely identifiable diffusion tubes for dynamically generating VOC and SVOC standard atmospheres at ppm and ppb concentrations for calibration of field and laboratory measurements

Abstract

Calibration of trace analyses for volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs) is an important but sometimes neglected aspect of environmental monitoring. Static methods using mixtures of VOCs in compressed air or nitrogen suffer from uncertain adsorptive losses on the gas cylinder wall and are not well suited for SVOCs. Dynamic methods enable generation of standards when needed, using permeation or diffusion tubes in thermostatted ovens through which a carrier gas flows whose flow-rate is user-controlled. We describe a new system of refillable diffusion tubes engraved with individual serial numbers (for quality systems traceability) that users can easily calibrate gravimetrically in a few weeks, compared with several months for gravimetric calibration of permeation tubes. These devices may be useful for calibrating ppm and ppb measurements of VOCs and SVOCs. Using appropriately low temperatures and an inert carrier gas, it may also be possible to generate standards for many labile and oxygen sensitive compounds.