STATISTICAL CONSIDERATIONS FOR THE DIRECT INTRODUCTION OF PARTICULATE SAMPLES FOR PLASMA EMISSION AND PLASMA SOURCE-MASS SPECTROMETRY

The statistical relationships for measurement uncertainties due to the discrete nature of particles in the direct analysis of powder samples with plasma sources are derived. Although the principles can be applied to direct analysis of particulates in general, the emphasis is placed on the introduction of powder samples by fluidized-bed and slurry nebulization methods. Uncertainties unique to the direct analysis of powders can be attributed to two main factors; random variation of the number of particles used for measurement, and homogeneity of the powder. Relationships for the compound uncertainty due to both these effects were derived applying Poisson and binomial distributions for binary mixtures. The compound variance is shown to be equal to the product of the average total number of panicles used for the measurement, and the fraction of particles containing the analyte in the bulk mixture. © 1990.