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This paper describes a calibration service NIST is offering that measures the effective diameter of particles suspended in liquids using electrical differential mobility analysis. Measurements are for particles with diameters in the range of 50 nm to 400 nm. Electrical differential mobility analysis separates aerosol particles based on the particle size dependence of their electrical mobility. This measurement method was chosen because it offers lower uncertainty for particles smaller than 400 nm compared to other methods. Detailed descriptions of the calibration system, operating procedures, and analysis method are included. Customer information regarding test sample requirements, measurement uncertainty analysis, and quality control procedures is also included in the paper. 1. Description of Service NIST is offering a calibration service to measure the effective diameter of particles suspended in liquids. The measurement method consists of nebulizing the particle suspension and measuring the size distribution of the particles in aerosol form by electrical differential mobility analysis. The service is primarily designed for measuring polystyrene latex (PSL) spheres in water with a narrow size distribution. Customers targeted are those who need to demonstrate NIST Traceability or who cannot use other techniques to measure the particles. Particles of mean diameter size in the range of 50 nm to 400 nm are measured with an expanded uncertainty (95 % confidence interval) of 1.5 % of the peak size. Plans are to expand the measurement ability to range from 20 nm to 800 nm. The calibration facility will be able to provide a certified peak particle diameter and size distribution results (not certified). In the future we plan to provide certified information regarding the standard deviation of the size distribution. Customers are asked to provide samples in aqueous suspensions in quantities of 5 mL to 50 mL of concentrated solutions (0.5 % volume fraction or higher). Dilute solutions will require at least 200 mL. The container should be insulated and shipped by next day mail to avoid extended exposure to high or low temperatures. 2. Design Philosophy and Theory This particle size calibration method uses the physical principle of electrical differential mobility analysis, which separates aerosol particles based on the particle size dependence of their electrical mobility. The particle’s electrical mobility Z is equal to the velocity U of a charged particle divided by the electrical field strength E.

Particle size measurements for spheres with diameters of 50 nm to 400 nm