A differential mobility analyzer and a Faraday cup electrometer for operation at 200-930 Pa pressure

We have developed a differential mobility analyzer (DMA) based on the DMA d evised by Seto et al. (1997) and a Faraday cup electrometer for measurement of nanometer-sized particles at a few hundred Pa and examined the operatin g characteristics of the DMA using the tandem DMA technique. The tandem DMA calibration establishes that the DMA successfully classifies particles in the 200-930 Pa pressure range. It was also found that the transfer function of the DMA follows the triangular transfer function and the resolution of the DMA is close to that given for an ideal case. As a standard of a minimu m pressure that may be probed with the present DMA system, 400 Pa is estima ted when the DMA operates with a 3 nl min(-1) sheath flow and a 1 nl min(-1 ) aerosol flow rate. (C) 2000 Elsevier Science Ltd. All rights reserved.