Crystallization of calcium oxalate from synthetic urine.

The precipitation of calcium oxalate from synthetic urine was followed from the disappearance of radioactive oxalate from solution. Rates of precipitation were also estimated from the time of appearance of crystals. Synthetic urine inhibited the rate of crystallization of calcium oxalate; this inhibition was a combined effect of ionic strength and specific inhibition by one or mroe components of the synthetic urine. Polyphosphate and polyacrylate ions strongly inhibited crystallization of calcium oxalate from synthetic urine; phosphonates, heparin, and polystyrene sulfonate showed much less inhibition. Inasmuch as citrate and pyrophosphate ions showed some inhibition, it seems that carboxylate and phosphate groups on a polymer chain are the most effective inhibitors.