01679naa a2200253 a 450000100080000000500110000800800410001910000170006024501460007726000090022352009430023265000090117565300210118465300180120565300240122365300080124770000260125570000200128170000160130170000190131770000310133670000220136777300360138910451182022-01-04       2000    bl uuuu     u00u1 u    #d1 aSILVA, F. V.  aPotentiometric determination of urea by sequential injection using Jack bean meal crude extract as a source of urease.h[electronic resource]  c2000  aA sequential injection system was proposed to accomplish the potentiometric determination of urea. This procedure used an ammonium tubular selective electrode to assess ammonium concentration produced by enzymatic hydrolysis of urea from Jack bean meal (Canar;alia ensiformis DC) crude extract. A gaseous diffusion device was coupled to the flow set-up allowing on-line sampling and suitable selectivity for determinations. A detection limit of 6.0 x 10 mol urea 1 ', a relative standard deviation of' 1.9% (n = 10) and a sampling rate of 20 samples h-1 ' were observed when 172 Sumner units (SU) of urease and 900 ul of sample were used. Results agreeing with a comparative method were obtained by the proposed procedure and the use of the crude extract solution combined with the sequential injection approach improved the performance, producing reproducible results and low costs in comparison with procedures using commercial enzymes.  aurea  aAmmonium tubular  aCrude extract  aSelective electrode  aSIA1 aNOGUEIRA, A. R. de A.1 aSOUZA, G. B. de1 aREIS, B. F.1 aARAÚJO, A. N.1 aMONTENEGRO, M. C. M. B. S.1 aLIMA, J. L. F. C.  tTalantagv.53, p.331-336, 2000.