Ammonia transport across hydrophobic membranes. Application to dialysate regeneration

Removal of ammonia from a recirculating dialysate buffer in a portable hemodialysis application can be achieved by countercurrent, gas phase ammonia transfer across a hydrophobic membrane into an acid solution. Ammonia transfer fluxes as high as 0.076 mumol/sec/m2 have been achieved using a Sarns Turbo Membrane Oxygenator (Sarns-3M, Ann Arbor, MI) with a 1.9 m2 membrane surface area (0.145 mumol/sec actual rate). A simple physical model based upon ammonia desorption at the gas-dialysate buffer interface in a membrane pore, ammonia diffusion through the gas filled pore, and subsequent ammonia absorption at the gas/acid interface side of the pore quantitatively describes the experimental data. The ammonia transfer rate is most dependent upon dialysate buffer pH (higher pH promoting transfer rate) and ammonia concentration in the dialysate buffer (higher concentrations promoting transfer rate). A 500 fold improvement in transfer rate, however, will be required for clinical application.