EVALUATION TESTS AND APPLICATIONS OF A DOUBLE-LAYER TUBE-TYPE PASSIVE SAMPLER

Validation tests on a thermally desorbable tube-type passive sampler filled with two different graphitized carbon blacks were conducted in order to determine the influence of air velocity and direction, concentration and sampling time on sampling rate. A specially made apparatus was used to study the behaviour of the passive sampler in dynamic artificial atmospheres. This apparatus permits the simultaneous sampling of 48 tubes at two different air velocities, minimizing errors due to random variations of the operating conditions during a prolonged sampling time, which allows a better stochastic analysis of data to be performed. The results were in agreement with those obtained by actively sampling the same test-tubes. The results of laboratory and field tests showed that the behaviour of tube-type devices having a small cross-section is independent of the environmental parameters checked over a wide range of operating conditions. The constant sampling rate with these samplers in the range from 30 min up to more than 12 h and the high sensitivity of thermal desorption methods allow the determination of organic species down to the ppb level. A field experiment on the evaluation of the indoor pollution in a domestic environment is also described. The use of a double-layer tube-type passive sampler, with the adsorbent of lower specific surface area positioned at the exposed side of the device, allows a better desorption efficiency. © 1990.