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AAPS PharmSciTech. 2003 September; 4(3): 62–70.
Published online 2003 June 4. doi:  10.1208/pt040336
PMCID: PMC2750629

Assessing the accuracy of routine photon correlation spectroscopy analysis of heterogeneous size distributions

Abstract

The aim of the current study was to investigate the ability of a fixed-angle routine photon correlation spectrometer (PCS) to resolve bimodal size distributions. The focus was on dispersions consisting of a majority of smaller and a minority of bigger particles. Monodisperse latex beads of sizes from 21 to 269 nm were measured first as single-size dispersions and then with various binary blends. For single-size dispersions, the mean diameters obtained were as indicated by the manufacturer, except for 21- and 34-nm particles, which were somewhat smaller. PCS analysis of blends of 21+102-nm and 34+102-nm particles resulted in bimodal distributions with particle diameters of the 2 peaks in the expected magnitude down to critical blending ratios of 0.002% and 0.08% of bigger particles, respectively. At these ratios, PCS results became inconsistent, and an increased number of monomodal results and/or high residuals were seen. For 21+102-nm blends, at even smaller ratios (0.001%), more consistent results were obtained again with predominantly monomodal distributions in the size range of the smaller particles (ie, the bigger particles were neglected). PCS analysis of blends of 21+269-nm particles yielded bimodal distributions with diameters within the expected magnitude as long as the content of bigger particles did not exceed 0.005%. Above this ratio, predominantly monomodal results with mean diameters in the magnitude of the bigger particles were obtained (ie, the smaller particles were neglected). In conclusion, a routine PCS instrument can resolve bimodal size distributions of colloidal dispersions only at certain ratios of the 2 subpopulations. Both low and high ratios lead to 1 of the 2 subpopulations being neglected.

Keywords: dynamic laser light scattering, quasielastic light scattering, latex colloids, particle size, size analysis

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
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Articles from AAPS PharmSciTech are provided here courtesy of American Association of Pharmaceutical Scientists