Thermogravimetry/mass spectrometry of urease-immobilized sol–gel silica and the application of such a urease-modified electrode to the potentiometric determination of urea Original Research Article

Urease has been immobilized in a sol–gel silica matrix, and the enzyme-fixed silica characterized by means of thermogravimetry/mass strectrometry and Fourier transform infrared (FTIR) spectroscopy. The former indicated that the urease immobilized in the sol–gel silica is thermally more stable than free urease. The FTIR spectrum of the urease-fixed silica results from the superimposition of the silica and urease spectra, confirming that the enzyme can be immobilized in the sol–gel silica without any chemical deterioration. The urease-fixed sol–gel silica electrode has been applied to the potentiometric determination of urea. A Nernstian relationship (slope 59 mV decade−1) was obtained for 1×10−5–5×10−2 M urea at pH 8.