An evaluation of radiocolloid sizing techniques.

Techniques for sizing radiocolloids are reviewed. The small size range (1-100 nm) of many radiocolloids and their polydispersity limit the choice of the technique used. To compare several techniques directly, the particle size of Technetium-99m sulfide colloid was studied using Nuclepore filtration, ultracentrifugation and electron microscopy. The last of these was adopted as the method of choice. Using this technique, the particle size and shape of colloids below 100 nm can be accurately determined. Technetium-99m antimony sulfide colloid and indium-113m hydroxide were then examined by electron microscopy, and the chemical nature of the particles was determined by x-ray fluorescence analysis. Results resolved the size discrepancies reported in the literature and demonstrated the importance of identifying the chemical nature of the particles under examination.