Ž . Spectrochimica Acta Part B 56 2001 11131126 Spatial aerosol characteristics of a direct injection high efficiency nebulizer via optical patternation  Michael G. Minnich, John A. McLean, Akbar Montaser  The George Washington Uni  ersity, Department of Chemistry, Washington, DC 20052, USA Received 30 December 2000; accepted 30 April 2001 Abstract Ž . Optical patternation is used to study the aerosol produced by a direct injection high efficiency nebulizer DIHEN , Ž . a micronebulizer used in inductively coupled plasma ICP spectrometries. The technique allows for the rapid and non-intrusive elucidation of the two-dimensional spray structure, planar mass distribution, spatial droplet size distributions, and spatial transient spray processes on the nanosecond-timescale. The aerosol cone diameter and the cone angle are reported at selected cumulative volume percent of the total aerosol and as a function of nebulizer gas flow and at three key axial locations from the DIHEN tip. Optical patternation reveals three major results for the Ž. DIHEN aerosol probed in the absence of the ICP torch: 1 the primary aerosol is spatially confined to a greater degree at a nebulizer gas flow rate of 1.0 lmin compared to 0.25 lmin, which is a flow rate commonly used by the Ž. DIHEN for maximal sensitivity in ICP mass spectrometry; 2 the aerosol rotates around the nebulizer axis, Ž . producing satellite droplets that are observed to a greater extent at lower nebulizer gas flow rates 0.25 lmin ; and Ž. 3 satellite droplets are more prevalent at distances farther away from the nebulizer tip. The implication of these diagnostic results on the analytical performance of the DIHEN for ICP spectrometries is discussed, particularly, in relation to noise, imprecision, sample  plasma interactions, and the residence time of droplets in the plasma.  2001 Elsevier Science B.V. All rights reserved. Ž . Keywords: Direct injection high efficiency nebulizer DIHEN ; Optical patternation; Aerosol diagnostics; Aerosol rotation; Aerosol cone angle; Aerosol cone diameter; Inductively coupled plasma spectrometry  This paper is published in the Special Issue of Spectrochimica Acta Part B dedicated to the late Professor Velmer A. Fassel.  Corresponding author. Tel.: 202-994-6480; fax: 202-994-2298. Ž . E-mail address: montaser@gwu.edu A. Montaser . 0584-854701$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 5 8 4 - 8 5 4 7 01 00234-8