Determination of volatile arsenicals in ambient air by flow injection

We report the development of a method for determining trans-dichloro(2-chlorovinyl)arsine (Lewisite) in ambient air in near real time. Air monitoring of Lewisite is required to support arms control treaty inspections, weapons destruction processes, and remediation of hazardous waste sites. Flow injection (FI) techniques are used to integrate a gas permeation membrane (GPM) sampling unit to a detector based on the constant-current mode of potentiometric stripping analysis (PSA). The method indirectly measures Lewisite in ambient air by collecting vapor-phase Lewisite across a thin-walled rubber membrane and hydrolyzing it to form arsenite ion for detection by PSA. We tested silicone and natural rubber nonporous membranes with estimated wall thicknesses of 0.66 and 0.27 mm, respectively. The rubber GPM tubes are oriented linearly in the sampler, and the sample is collected at a flow rate of 200 ml/min through the cavity. We studied arsenic trichloride as a vapor-phase simulant for Lewisite, although we found its silicone rubber permeability characteristics unfavorable. Factors including membrane tube length, sampling time, and sampling temperature were examined during experiments in which vapor-phase Lewisite was generated at 0.99 ppbv. The typical response to Lewisite was fast (within one sampling cycle) and continuous readings to vapor-phase Lewisite measurements were stable (<20% relative standard deviation). On the basis of this testing, we estimate a working range for Lewisite from 0.5 to 50 μg/m3 using a 15 min total cycle time.