Performance of a Scanning Differential Mobility Analyzer

The performance of a scanning differential mobility analyzer (DMA) combined with a condensation nucleus counter (CNC) having high detection sensitivity has been evaluated using monodisperse latex particles of 100 nm in diameter and polydisperse sodium chloride particles between 10-120 nm: 1) A method is proposed to accurately measure the delay time between the DMA outlet and the particle detector of the CNC, which is necessary to measure the particle size distribution by the scanning DMA. 2) The effect of some operating factors, such as CNC counting time and time constant of the exponentially increasing voltage on minimum achievable scanning time is examined by the experiment, and theoretical discussion is made on the basis of the mobility transfer function of particles classified by the DMA, which is related to the mobility shift during the CNC counting time. As a result, accurate measurement of monodisperse particles is completed in about 10 sec. For polydisperse particles, it takes only about 30 sec.