Accurate nanoparticle size determination using electrical mobility measurements in the step and scan modes

Abstract

A critical and extensive comparison was made between differential mobility analysis (DMA) measurements of the mean diameter of monodisperse gold nanoparticles (AuNPs), based on step-voltage mode and the more commonly used scan-voltage mode (commercially known as scanning mobility particle sizer, SMPS). Under specific conditions including a long scan time, the difference between mean diameters measured by the two modes of operation was less than the expanded combined uncertainty (95% confidence interval) for the step-voltage mode. In addition, a comparison was made between two different calibration methods for DMA: the use of a certified nanoparticle size standard (artifact) versus a direct measurement of the sheath flow rate. Important variables and limitations for accurate measurements by the scan-voltage method were identified and evaluated. The mean size shifts to smaller electrical mobility diameters as the scan time is reduced and the scan mode is unable to measure sufficient points across the peak of very narrow size distributions, leading to systematic errors. The use of a calibration particle corrects for the flow and DMA column geometric effects and was found to minimize the effect of a reduced scan time. A methodology is presented for the use of these AuNPs and other monodisperse calibration particles for accurately calibrating SMPS instruments for the measurement of the electrical mobility diameter distribution.

Copyright © 2022 American Association for Aerosol Research

Graphical Abstract

Editor:

• Jason Olfert

Acknowledgments

We thank Blaza Toman at NIST for assistance with the Type A uncertainty analysis. The representative SEM images were provided by Dr. Andras Vladar of the NIST Physical Measurements Laboratory.

Disclosure statement

The authors report there are no competing interests to declare.

Notes

1 Commercial equipment, instruments, or materials identified in this paper are intended to specify the experimental procedure adequately. Their use is not a recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Additional information

Funding

KD was supported in part by a grant from the National Institute of Standards and Technology, Materials Measurement Science Division (Award No. 70NANB17H057).