Hello, Members of the List, About two months ago, Frank Key contributed very generously some techniques for fractionating EIS into its constituent species of silver, ionic and particulate. These were ultracentrifugation and freezing. The latter is, of course, the more readily available technique for most people. But the particulate (colloidal) fraction is lost by this separatory technique.
According to Herbert Freundich, the standard method for separating and purifying colloids for many years had been the original method discovered by Thomas Graham. This is fractionation by semipermeable membranes. Using this method, the colloid is not lost. Modern microfilters, utrafilters and nanofilters can be be bought for 1 or 2 dollars apiece when purchased in lots of a hundred. A century ago, parchment was used and did a reasonably good job. Perhaps other natural semipermeable membranes exist that will purify or condense colloids by removing the dissolved ionic fraction from EIS. Has anybody tried this? Best regards, Matthew
