OPTICAL DEPTH OF FIELD EFFECTS IN PARTICLE-SIZE ANALYSIS BY LASER DIFFRACTOMETRY

A nonlinear overestimate of the median droplet diameter measured by laser diffractometry in aerosols of interest in atomic spectrochemical analysis is found to result if the aerosol path traversed by the laser exceeds the optical depth of field characteristic of the diffractometer. The depth of field of a Leeds and Northrup diffractometer is found to be 4. 4 cm. The magnitude of the error in apparent median droplet diameter is plus 21% for aerosols emergent from 10 cm slot burners used in flame spectrochemical analysis. Additional data are included for a variety of aerosol path lengths over the range 0. 5 to 20 cm.