title: Determination of urea in serum by using naturally immobilized urease in a flow injection conductimetric system.
abstract: A flow injection method was developed, aimed at the determination of urea in human serum. The system makes use of the naturally immobilized urease present in Canavalia ensiformis DC (jack bean). A column is filled with small pieces of this bean, and the sample (50 microliters) containing urea passes through it carried by a 1% NaCl solution. On leaving the column the stream is merged with an alkaline reagent (0.5 mol dm-3 NaOH; 0.5% disodium dihydrogen ethylenediaminetetraacetate). The ammonium ions, arising from the enzymatic reaction that occurs inside the column, are changed into the molecular form, which permeates a polytetrafluoroethylene membrane and is received in a de-ionized water acceptor stream. The ammonia ionizes causing an increase in the conductance, which is proportional to the urea content of the sample. About 40 samples can be processed in 1 h with negligible carry-over and with a relative standard deviation of 1% or less. The results are in agreement with those obtained by a standard spectrophotometric method.
authors.affiliation: Instituto de Química, Universidade Estadual de Campinas CEP 13081, São Paulo, Brazil.
authors.forename: L C
authors.initials: LC
authors.lastname: de Faria
authors.forename: C
authors.initials: C
authors.lastname: Pasquini
authors.forename: G
authors.initials: G
authors.lastname: de Oliveira Neto
mesh_terms: D003217:Conductometry / Q000379:methods* / Q000706:statistics & numerical data; D004800:Enzymes, Immobilized; D006801:Humans; D006863:Hydrogen-Ion Concentration; D014508:Urea / Q000097:blood*; D014510:Urease / Q000037:antagonists & inhibitors
chemical_list: D004800:Enzymes, Immobilized; D014508:Urea; D014510:Urease