Urea Determination in Human Sera With an Ammonium Ion Selective Electrode Made With Solid Inner Electric Contact and Immobilised Urease

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Abstract
A PVC matrix nonactin based membrane electrode assembled with a solid carbon-epoxy inner electric contact has been successfully used in ammonium and urea analysis. Different buffers have been tested and sodium and potassium interferences have been evaluated in order to obtain the best calibration curve for determination of ammonium and urea in serum samples. Three immobilization techniques for the enzyme urease have been compared. Nylon net immobilization procedure was found to have the best analytical features when coupled with this electrode and it has been selected for urea determination in sera. Results were in good agreement with those obtained with the clinical standard spectrophotometric method.