SEQUENTIAL ANALYTE REMOVAL IN FLOW-ANALYSIS - DETERMINATION OF NITROGEN, PHOSPHORUS AND POTASSIUM IN FERTILIZERS

A new approach for multiparametric determinations in now analysis base d on successive sequestering of analytes is proposed and exemplified i n the determination of water soluble nitrogen, phosphorus and potassiu m in fertilizers. The analytes are partially and reproducibly removed from the sample zone in the main stream towards specific analytical ch annels without significant alterations in the flowing sample plug. By using gas diffusion, dialysis and asymmetric stream splitting, ammoniu m, potassium and orthophosphate ions are stripped out and determined b y flow potentiometry, flame photometry and spectrophotometry, respecti vely. The system permits up to 75 samples to be examined per hour, req uires 90 mg tris(hydroxymethyl)aminomethane plus 75 mg ammonium heptam olybdate tetrahydrate plus 75 mg ascorbic acid per sample, and yields reproducible results (R.S.D. usually < 3%) in agreement with usual man ual procedures. The feasibility of an analogous modular system with a random selection of procedures is discussed.