Mass distribution of chemical species in a polydisperse aerosol: Measurement of sodium chloride in particles by mass spectrometry

Abstract

A continuous, real-time method for measurement of the mass distribution of chemical species in aerosol particles by mass spectrometry is described. Individual particles of sodium chloride from a polydisperse aerosol are introduced in the form of a beam into a miniature oven (∼28 mm 3 volume) placed in the ion source of a quadrupole mass spectrometer. The oven is made from rhenium metal sheet (0.018 mm thick) and maintained at 1600 K. The intensities of sodium ions resulting from individual particles by thermal volatilization and surface ionization inside the oven are measured with the quadrupole mass spectrometer. Masses of sodium chloride particles are obtained from these intensities using a predetermined calibration curve of the mass spectrometer signal with mass. The results are corrected for the particle transmission efficiency of the beam generator used for sample introduction into the ion source, and also for inhomogeneity im radial distribution of different size particles across the beam. The number versus mass distribution is in good agreement with the distribution determined from electron microscopy of the aerosol sample collected on a nucleopore filter. The application of mass distribution measurements to the design of nebulizers and other spray devices for the dispersion of drugs and diagnostic agents is discussed.