An evaluation of methods for sizing radiocolloidal particles.

Technetium-99m-labelled colloids covering the entire spectrum of particle size were prepared from commercial kits (antimony colloid, sulphur colloid, tin colloid) or by chemical (excess aluminium) or thermal modification of sulphur colloid (heating time of 30 min). Particle size measurements were obtained using electron microscopy and/or a laser light scattering technique. The results for antimony colloid agreed reasonably well for both techniques with a range of 3 to 25 nm. However, standard sulphur colloid had a smaller size (220 nm) when measured by electron microscopy in comparison to the larger size (390 nm) obtained with the light scattering method. This discrepancy was felt to be due to artefacts created by electron microscopy. These artefacts (drying and sublimation) were avoided by the laser light scattering techniques which has the advantage of being non-destructive and of quickly sizing particles while still in solution. The larger colloidal particles were sulphur colloid doped with aluminium ions (1000 nm) and the tin colloid (2500 nm) which were sized by electron microscopy and laser light scattering respectively.