DIRECT DETERMINATION OF AMMONIUM IN SOLID SAMPLES BY AUTOMATIC FLOW PROCEDURES

Two new approaches to the determination of ammonium in solid samples u sing flow systems and photometric detection are presented. Both allow the direct determination of this analyte as gaseous ammonia, and simpl ify the treatment of the samples by reducing their manual manipulation . One of the manifolds used incorporates an absorbing solution held in a mini-chamber, whereas the other is based on a flow-through gas-diff usion probe. Both methods allow the ammonium to be determined at mu g g(-l) level with relative standard deviations between +/- 3% and +/- 5 %. The performance of the two methods was tested by analysing both syn thetic and real (soil) samples. Nitrogen availability and extractable ammonium nitrogen in soil were determined by using the proposed method ologies.