Analytical Sciences

Measurement of Cluster Ions and Residue Nanoparticles from Water Samples with an Electrospray/Differential Mobility Analyzer

Bangwoo HAN,*^,** I. Wuled LENGGORO,* Mansoo CHOI,**^,*** and Kikuo OKUYAMA* 

*Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
**School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea
***National CRI Center for Nano Particle Control, Institute of Advanced Machinery and Design, Seoul National University, Seoul 151-742, Korea

Cluster ions and residue nanoparticles with sizes below 30 nm were generated by electrospraying (ES) and drying droplets of pure water, tap water, and aqueous solutions of salts. The mobility spectra of the cluster ions between 9.1 and 9.3 x 10^-5 m²/(V s) were measured using a differential mobility analyzer (DMA) operated at room temperature and atmospheric pressure. A modified Faraday cup and a condensation nucleus counter were used for detection. The concentrations of total residue/contaminants in the water were determined as a function of sizes of measured aerosol particles and of the initial droplets. Method detection limits were at sub-ppb level for pure water and sub-ppm level for tap water. ES/DMA is capable of simultaneously measuring the mobility distribution of cluster ions and concentration of total residue present in water samples.

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