TURBIDIMETRIC FLOW-INJECTION DETERMINATION OF TOTAL NITROGEN AND POTASSIUM IN VEGETABLES

A turbidimetric flow-injection system was developed for the determinat ion of total nitrogen and potassium in vegetable samples using a singl e spectrophotometer as detector. As a precipitating agent, 3.0% (w/v) sodium tetraphenylboron solution prepared in 2.0% (w/v) poly(vinyl alc ohol) was used. A gas diffusion process was included in the manifold t o separate ammonium ions from the rest of the sample and to allow pair ed analysis. Total nitrogen and potassium determinations were carried out on the solutions remaining in the acceptor and donor streams, resp ectively. Results obtained were precise (relative standard deviations <2.1 and 1.6% for total N (<25 mg g(-1)) and K (<55 mg g(-1)) determin ations, respectively) and in agreement with those of reference methods . Analysis can be carried out at a rate of up to 35 samples per hour ( corresponding to 70 determinations per hour) within concentration rang e 87-430 mg N-NH4+ l(-1) and 78-390 mg K+ l(-1) for the total nitrogen and potassium determinations, respectively. (C) 1997 Elsevier Science B.V.