An automatic flow ultramicroscope for submicron particle counting and size analysis

• Published in: Journal of colloid and interface science Vol. 45; no. 3; pp. 573 - 583
• Main Authors: Mcfadyen, Peter, Smith, Alec L
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.01.1973
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(73)90174-4

A laser illuminated automatic flow ultramicroscope particle counter designed for submicron sized colloids is described. It makes use of a fine capillary which, in conjunction with further hydrodynamic focusing, confines the particles to a narrow stream in which they are all counted. This instrument is shown to meet the criteria necessary for reliable operation with a number of colloidal dispersions. Its advantages include: (a) the high rate of counting provides good statistical results with high reproducibility in a short time; (b) particles well below 1 μm diameter can be counted, the actual lower size limit depending to some extent on the optical properties of the components of the dispersion; (c) the low shear rates applied to particle aggregates allow measurements to be made on coagulating systems without introducing errors due to peptization within the instrument; (d) the possibility of extending the instrument's application to the analysis of particle size with reliable results at the small particle end of the distribution. An alternative version which counts only a proportion of the illuminated particles as defined by an ocular diaphragm in the microscope system is shown to be subject to serious errors due to “edge effects.” As a result, absolute calibration of such an instrument is not feasible.