[Gel model for measuring crystallization inhibitor activity]

In an attempt to develop a method with the most favourable possible relationship of information gained to expenditure of material and time a simple way of measuring crystallisation inhibitor activity was developed. Calcium and oxalate ions are diffused against each other out of two opposite start holes in a layer of gel on a microscopic slide and form a strip of calcium oxalate crystals where they meet in the middle. The substances influencing crystallisation are allowed to diffuse into this central area. The density and extent of the calcium oxalate strips vary according to the inhibitory effect of the substances used. These differences were registered by means of photometric measurement for comparison against a control without any inhibitor added and an inhibition index was computed. Some of the best-known inhibitors were tested and also show a defined effect in this model. In physiological concentrations magnesium and citrate can be said to have particular importance. The range of inhibitory activities to be expected of human urine is covered by the present model.