Solid-phase separation of 14C-labelled urea and aminoisobutyric acid for membrane transport studies

A sorbent extraction method has been developed for separating 14C-labelled urea and aminoisobutyric acid (AIB) in blood. The use of commercial solid-phase extraction cartridges containing aminopropyl-bonded silica provided a convenient and rapid separation of urea and AIB with better than 92% recovery of each and less than 5% cross-contamination. This allows these compounds, together with [3H]methylglucose, to be used as marker compounds for investigating three aspects of membrane transport. The facility to separate any two of the three compounds permits their simultaneous measurement, greatly increasing the amount of data obtainable from each in vivo preparation.