DETECTOR SLIT WIDTH ERROR IN MEASUREMENT - OF LATEX PARTICLE-SIZE DISTRIBUTIONS WITH A DISK CENTRIFUGE

An expression for the turbidity is derived for a polydisperse distribution of particles in a detection zone having a finite slit width. It is shown that the turbidity is proportional to the differential volume distribution and decreases as the particles spread radially outward by a dilution effect. Furthermore, the first moment of the diameter about the turbidity - extinction coefficient ratio in time space yields the number average diameter. This paper reports an investigation of possible errors in particle size distribution and averages resulting from the finite size of the detector slit width. The previously reported derivation of turbidity accounting for the finite slit width by Treasure and Coll and Haseler is not rigorously correct. A more rigorous derivation is presented in this paper along with an error analysis of the effect of finite slit width on particle size values. Mixtures of nearly monodisperse latexes with closely spaced sizes analyzed by the disc centrifuge over a range of normal operational variables demonstrate that the error due to finite slit width is well within the observable experimental error of the method and as a practical matter can be neglected.