Time-of-flight ion mobility spectrometry

Abstracts

694

(241Am, 1.84 mCi). The mean mobilities in clean air were found to be 1.1-1.2 cm2V-i s-i for positive ions and 1.8-2.0 cm2 V-’ s-i for negative ions, respectively. As a tracer in the carrier gas we used a mixture of SO,-Hz0 (10 ppm, RH y 10%) or alternatively acetone ( N 6000 ppm). As an overall result, both SOs-Hz0 and acetone were observed to have an effect on the ion mobilities in the neutralizer. Furthermore, in the S02-HZ0 system formation of nanoparticles was detected. Using acetone as a tracer, no particle formation was observed, but the positive ion mobility spectrum was found to be extremely narrow, nearly monodispersed.

TIME-OF-FLIGHT Terhi Mattila, Department

of Physics,

ION MOBILITY

Gunnar Tampere

Graeffe, University

Marko

Riihela

of Technology,

SPECTROMETRY and Jorma

Keskinen

P.O. Box 692. 33101 Tampere,

Finland

Abstract-In a time-of-flight type ion mobility spectrometer, ions are separated in an electric field according to their drift time (time-of-flight spectrum). The instruments are normally operated at elevated temperatures (ZOOC) in order to avoid cluster formation. The measurable concentration of the sample is limited by the amount of charge produced by the radioactive source. In this study, a time-of-flight type ion mobility spectrometer was operated at room temperature to study the effect of concentration on drift time (mobility). A laboratory test instrument with a cylindrical drift tube (Mattila et al., 1991) was used to study the shape of the spectra under NTP-conditions. At room temperature, cluster ion formation is very important. It was found that the identity of the measured ions changes with the concentration. Even concentrations higher than 1000 ppm were measured. Mattila, T., Tyrvainen, H. and Graeffe, Science, No. 19 (Edited by Mattsson,

G. (1991) Ion mobility spectrometer (IMS). In Report R., Hameri, K. and Kulmala, M.), pp. 134-138.

REAL TIME SIZE DISTRIBUTION MEASUREMENT ELECTRICAL LOW PRESSURE IMPACTOR J. Keskinen,* *Physics

M. Moisio,*

Department, Tampere ‘VTT Manufacturing

K. Pietarinen*

Series in Aerosol

WITH

and M. LehtimZki+

University of Technology, Box 692, SF-33101 Tampere, Technology, Box 1701, SF-33101 Tampere, Finland

Finland

Abstract-Recently, a new instrument for the real time measurement of aerosol size distribution was introduced. This electrical low pressure impactor (ELPI) is based on combining electrical detection principle with low pressure impactor size classification. The measurement principle and instrument configuration have been described by Keskinen et al. (1992). Application results of full scale power plant combustion aerosol measurements are reported, showing good agreement with gravimetric results. A fast measurement system has been constructed for fuel pyrolysis studies, with a time response of less than 1 s for size distribution measurement. The instrument has also been applied to filter grade efficiency measurement. The grade efficiency of EUS and EU8 fibrous filters has been measured in the size range 0.042 pm. The efficiency values agree with the results obtained using OPC and DMA. Keskinen,

J., Pietarinen,

K. and Lehtimaki,

M. (1992) Electrical

low pressure

impactor.

J. Aerosol Sci. 23, 353.

THE USE OF POLYDISPERSE POLYSTYRENE AEROSOLS FOR DETERMINING SAMPLER CHARACTERISTICS WITH AN APS A. Gudmundsson,* *Lund

G. Lid&n+ and B. Paulsson’

Institute of Technology, Department of Working Environment, Lund, Sweden ‘National Institute of Occupational Health, Solna, Sweden

Abstract-Polydisperse polystyrene aerosols were generated from a solution of polystyrene in a mixture of toluene and pentamethylbenzene. The solution was atomized, and dried in a drying tower, neutralized and fed into an experimental box. Depending on polystyrene concentration the surface of the generated particles varied from