ION-SPECIFICITIES OF SULFITE AND PHOSPHAT E ION ENZYME SENSORS

A sulfite ion enzyme sensor was prepared by cross-linking sulfite oxid ase with bovine serum albumin using glutaraldehyde on the flat end of a platinum disk electrode silanized with 3-aminopropyltrimethoxysilane . Similarly, a phosphate ion enzyme sensor was made by coimmobilizing purine nucleoside phosphorylase and xanthine oxidase on the flat end o f a glassy carbon disk electrode. A sulfite sensor was based on the am perometric detection (0.6 V vs. Ag/AgCl) of hydrogen peroxide produced by an enzymatic reaction; the current response was linearly related t o the sulfite concentration over the range of 5 X 10(-7)-5 X 10(-4) M. This sensor was highly selective for sulfite, except for a small resp onse to nitrite, thiocyanate and thiosulfate. A phosphate sensor gave a response when inosine (5 mM) was added to a 0.1 M borate buffer solu tion (pH 7.5) containing phosphate. This sensor was based on the amper ometric detection (0.5 V vs. Ag/AgCl) of uric acid produced by two suc cessive enzymatic reactions. The current response was linearly related to the phosphate concentration over a range of 5 X 10(-7) approximate ly 2 X 10(-5) M at 37 +/- 0.2-degrees-C. This sensor was essentially s pecific for phosphate.