A simple method for the simultaneous measurement of sodium and chloride fluxes across transporting epithelia.

A simple technique for the separation of 22Na and 36Cl radioactivity in the same solution is described. Two samples were taken from a solution containing both 22Na and 36Cl. One sample was precipitated with AgNO3 and the other was untreated. Samples were assayed for radioactivity by liquid scintillation spectrophotometry. Precipitation with AgNO3 removed 100% of the 36Cl activity from solution while having no effect on the 22Na radioactivity. Thus precipitated samples contained only 22Na radioactivity. Subtraction of the radioactivity in the supernatants of precipitated samples (i.e. 22Na) from the total radioactivity of untreated samples (i.e. 22Na and 36Cl) yielded the level of 36Cl activity in these samples.