title: 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.
authors: Department of Pharmaceutics and Biopharmaceutics, Institute of Pharmacy, University of Tromso, 9037 Tromso, Norway.
authors: Christer B
authors: CB
authors: Frantzen
authors: Lars
authors: L
authors: Ingebrigtsen
authors: Merete
authors: M
authors: Skar
authors: Martin
authors: M
authors: Brandl
mesh_terms: D002627:Chemistry, Physical / Q000295:instrumentation / Q000379:methods / Q000592:standards; D003102:Colloids / Q000737:chemistry* / Q000378:metabolism*; D007834:Lasers; D008027:Light; D008863:Microspheres; D010316:Particle Size; D017785:Photons; D012542:Scattering, Radiation; D013057:Spectrum Analysis / Q000295:instrumentation / Q000379:methods / Q000592:standards*
chemical_list: D003102:Colloids