Effects of urine pretreatment on calcium oxalate crystallization inhibition potentials

Activated carbon and calcium oxalate solids have been used as adsorbents to remove crystallization inhibiting species from centrifuged and dialyzed normal urines. The urine supernatants, following adsorption treatments, have been examined for their calcium oxalate monohydrate crystallization inhibitory potentials by means of a constant composition potentiostatic seeded growth method. The supersaturation of the reactant solution was maintained constant during the crystallization process by the potentiometrically monitored addition of solutions containing crystal lattice ions controlled by a specific calcium ion selective electrode. The experimental results indicate that normal urine contains a number of inhibiting species of variable molecular weight and adsorbability. In addition, preliminary results indicate that substances present in normal urine interfere substantially with the adsorption of crystallization inhibiting species by calcium oxalate monohydrate crystal surfaces. Both charcoal and CaOx adsorbents have been successfully used to completely remove a synthetic, model urinary crystallization inhibitor, ethylene-diamine-tetramethylene-phosphonic acid, ENTMP, from relatively concentrated solutions in 0.15 M NaCl.