LABORATORY DEVELOPMENT AND FIELD-EVALUATION OF A PASSIVE SAMPLING DEVICE FOR MONOMETHYLHYDRAZINE IN AMBIENT AIR

A passive sampling method applicable to personnel and area monitoring was developed for the quantitation of monomethylhydrazine (MMH) in amb ient air at sub part-per-million levels. The method involves the use o f a black, molded, low-density polyethylene sampler consisting of a di ffusion barrier and a citric acid collection medium. It collects sampl es that can be analyzed by NIOSH colorimetric methods of a coulometric titration procedure. The sampler incorporates a two-millimeter thick diffusion barrier with 144 one-millimeter diameter holes and produces a collection rate for MMH of 27 cm(3)/min. The accuracy of data collec ted is within 30% of actual values under most conditions. The dosimete r has demonstrated accuracy for sampling periods of 15 min to 66 hours when sampling MMH at the threshold limit value concentration of 200 p pb. Limits of detection are dictated by the specific analytical method . Coulometric titration will detect exposures of 30 ppb-hours. Laborat ory tests were conducted in controlled atmospheres to evaluate collect ion rate, face velocity effects, relative humidity effects, sample sta bility, reproducibility, linearity, and interference effects of select ed chemical vapors. Field tests evaluated performance under typical co nditions. Test locations were selected to provide information on proba ble interferents. A double-blind protocol was used involving industria l hygienists, analytical chemists, and auditors. The data obtained rev ealed a performance problem not encountered in the laboratory. The cau se was identified and the prototype system was modified and retested. Results from the modified sampler show that it is suitable for workpla ce monitoring applications with two minor interferents: tobacco smoke and intense direct sunlight.