AMPEROMETRIC ENZYME ELECTRODE FOR THE DETERMINATION OF URINE OXALATE

An enzyme electrode has been developed for the simplified determinatio n of oxalate in human urine. Oxalate oxidase has been co-immobilised w ith bovine serum albumin (BSA) using glutaraldehyde between polycarbon ate or haemodialysis external membranes and an internal cellulose acet ate membrane to form a classical oxidase enzyme laminate construction. The underlying cellulose acetate permselective barrier confers the re quired selectivity for H2O2 over the interferent constituents of urine . Prior dilution and acidification of urine samples has enabled optimi sation of enzyme activity and therefore electrode response characteris tics for low level oxalate assay. Sequestering of singly and doubly ch arged cations in urine by ethylenediaminetetraacetic acid (EDTA) has e nsured release of bound oxalate, so permitting near total (>98%) deter mination of urinary oxalate. An outer substrate diffusion Limiting mem brane has proved critical to an electrode linear response within the c linical concentration range. Determination of human urinary oxalate in the concentration range 2-200 mu M in diluted urine (corresponding to 80-800 mu M oxalate in undiluted urine) has been possible. Results co rrelate well (r(2)=0.971; y=1.11x+4.20; n=20) with standard spectropho tometric determinations (x) performed within a hospital laboratory.