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Howard A Johnsen

Kenneth R Hencken

David W Hahn

William L Flower

This invention pertains generally to a method for improving the accuracy of particle analysis under conditions of discrete particle loading and particularly to a method for improving signal-to-noise ratio and instrument response in laser spark spectroscopic analysis of particulate emissions. Under conditions of low particle density loading (particles/m.sup.3) resulting from low overall metal concentrations and/or large particle size uniform sampling can not be guaranteed. The present invention discloses a technique for separating laser sparks that arise from sample particles from those that do not; that is, a process for systematically 'gating' the instrument response arising from 'sampled' particles from those responses which do not, is dislosed as a solution to his problem. The disclosed approach is based on random sampling combined with a conditional analysis of each pulse. A threshold value is determined for the ratio of the intensity of a spectral line for a given element to a baseline region. If the threshold value is exceeded, the pulse is classified as a 'hit' and that data is collected and an average spectrum is generated from an arithmetic average of 'hits'. The true metal concentration is determined from the averaged spectrum.

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Livermore, CA, United States of America

Howard A Johnsen