Accuracy of particle sizing

Calculations of average particle size, specific surface area, or particle population of a mixture may be based on either a differential or a cumulative analysis. In principle, methods based on the cumulative analysis are more precise than those based on the differential analysis, since when the cumulative analysis is used, the assumption that all particles in a single fraction are equal in size is not needed. The accuracy of particle-size measurements, however, is rarely great enough to warrant the use of the cumulative analysis, and calculations are nearly always based on the differential analysis. 

Egermann H. 1974. Dosage accuracy of singly dosed, stable drug forms with a small content of active substance. II. Influence of particle size on the homogeneity of the distribution of the active substance. Sci. Pharm. 42(1) 1-19. 

With sizing techniques that count the particles, it is desirable to know the accuracy of the size distribution after counting a given number of particles. Figure 2.4 gives the number of particles to be counted to give a specific accuracy [3]. For a less than 1% error in a given size... 

Detection limit, quantification limit, accuracy, and specificity are not normally considered appropriate for validation of particle sizing methods. 

Efforts have been made over the past several years to identify airborne metals with specific emission sources by the use of enrichment factors, and by comparing the trace element profile of airborne particles with characteristic components in particulate matter from various sources. Measurements of particle size and the application of sophisticated statistical techniques should increase the accuracy of these "fingerprinting approaches. 

Scales, P.J. and Jones, E., Effect of particle size distribution on the accuracy of electroacoustic mobilities, Langmuir, 8, 385, 1992. 

Figure 41.1 shows, for illustrative purposes, the fracto-grams for two different size ranges of polystyrene latex microspheres. (Polystyrene latex standards with narrow size distributions are ideal probes for testing the resolving power and accuracy of particle characterization methods. Those techniques unable to resolve close-lying latex... 

Recently a review asking the need for accuracy in reporting size parameters for pol)meric nanoparticles has been published.Although this review focused on polymeric nanoparticles, the same holds true for the lipid nanoparticles field. For accurate presentation of particle size data, all parameters (instrument, measurement principle, assumptions, calculation mode etc.) should be given and the limitations of the methods need to be considered. 

An operator with good technique is necessary in order to obtain reliable results with minimal systematic errors. Operator technique can influence accuracy of microscopic determination of particle size. There is a natural tendency for an operator to pay greater attention to large particles as he is less likely to miss them. Not only do small particles tend to be missed, they also pose problems by being hidden by the larger particles or appearing as clumps. However, in volumetric terms, small particles have a lesser influence. 

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