ELECTRON-MICROSCOPY OF AQUATIC COLLOIDS - NON-PERTURBING PREPARATION OF SPECIMENS IN THE FIELD

This paper describes a simple and powerful procedure for the specimen preparation of aquatic colloidal particles prior to direct observation by transmission electron microscopy (TEM). Four preparation schemes are described. For waters containing sufficiently large concentrations of colloids, aqueous solutions of particles are mixed with Nanoplast, a water-soluble embedding resin, and centrifuged over specimen grids placed on a horizontal disc; after curing, the resulting film has optimum quality for studies of particles at ultra-high resolution (greater-than-or-equal-to 1 nm). For waters with low concentrations of colloids, or when size fraction is desired, particles are collected directly on a TEM grid placed at the bottom of a centrifugation tube; after deposition and curing of a film of Nanoplast over the specimen, the grid can be used directly for TEM observation. The advantages of these methods, and of two other applications of Nanoplast for aquatic and sediment particles, are compared to those of classical specimen preparation schemes. A large number of specimens may be quickly prepared in the field, using the above procedures; at the same time, most of the preparation artefacts linked to classical procedures are avoided. The new procedures should help to make TEM a semi-routine analysis method for studying the nature and behaviour of aquatic colloids.