PRECONCENTRATION BY FLOW REVERSAL IN CONDUCTOMETRIC SEQUENTIAL INJECTION-ANALYSIS OF AMMONIUM

A simple sequential injection method for the determination of ammonium with conductometric detection is described. The sample and alkaline s olution are sequentially aspirated into a single tubular channel and m ixed by flow reversal. The formed ammonia permeates through a gas perm eable membrane and is collected on a static acceptor solution. The cha nge in conductance of the acceptor solution is related to the concentr ation of ammonium ions in the sample. The use of flow reversal and inf luence of sample residence time on preconcentration are studied. The d etection limit can be lowered from 1.5 mg L(-1) to 0.1 mg L(-1) if pre concentration by successive sample flow reversal is used. The relative standard deviation is lower than 3%.