Particle size determination using turbidimetry. Capabilities, limitations and evaluation for on-line applications

There are numerous reports of the use of turbidimetry for the determination of either the particle size or the particle size distribution (PSD) for a variety of latex systems. There has been a controversy in the literature, on whether turbidimetric techniques are at all capable of providing a valid estimate of the particle size distribution of a suspension. When attempting to estimate the PSD in poly(vinyl acetate) latexes in our laboratories using specific turbidity measurements and assuming log-normal distributions we observed that the parameters of the estimated distribution were so highly correlated that effectively an infinite number of distributions could adequately explain the data. However, all these alternative solutions were found to correspond to distributions having the same weight average diameter. We also observed that the behaviour of the solution during the parameter estimation was very dependent: i) on the value of m of the suspension; ii) on the actual particle size of the suspension and iii) on the turbidimetric technique used.