Abstract
A passive sampling method applicable to personnel and area monitoring was developed for the quantitation of monomethylhydrazine (MMH) in ambient air at sub part-per-million levels. The method involves the use of a black, molded, low-density polyethylene sampler consisting of a diffusion barrier and a citric acid collection medium. It collects samples that can be analyzed by NIOSH colorimetric methods or 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 cm3/min. The accuracy of data collected is within 30% of actual values under most conditions. The dosimeter has demonstrated accuracy for sampling periods of 15 min to 66 hours when sampling MMH at the threshold limit value concentration of 200 ppb. Limits of detection are dictated by the specific analytical method. Coulometric titration will detect exposures of 30 ppb-hours. Laboratory tests were conducted in controlled atmospheres to evaluate collection rate, face velocity effects, relative humidity effects, sample stability, reproducibility, linearity, and interference effects of selected chemical vapors. Field tests evaluated performance under typical conditions. Test locations were selected to provide information on probable interferents. A double-blind protocol was used involving industrial hygienists, analytical chemists, and auditors. The data obtained revealed a performance problem not encountered in the laboratory. The cause was identified and the prototype system was modified and retested. Results from the modified sampler show that it is suitable for workplace monitoring applications with two minor interferents: tobacco smoke and intense direct sunlight.