Development of a new chemically modified carbon paste electrode for selective determination of urinary and serum oxalate concentration

The construction and evaluation of a novel modified carbon paste electrode with high selectivity toward oxalate ion are described. The constructed carbon paste potentiometric sensor for oxalate ion is based on the use of a zirconium salan complex as a good ionophore in the carbon paste matrix. The electrode exhibits a Nernstian slope of 29.1 mV/decade to oxalate ion over a wide concentration range from 1.5×10−6 to 3.9 ×10−2 mol L−1 with a low detection limit of 7.0×10−7 mol L−1. The electrode possesses fast response time, satisfactory reproducibility, appropriate lifetime, and most importantly, good selectivity toward C2O42− relative to a variety of common anions. The potentiometric response of the electrode is independent of the pH of the test solution in the pH range 2.5–8.0. The modified carbon paste electrode was successfully applied as an indicator electrode in potentiometric titration and potentiometric determination of oxalate ion in mineral water, blood serum and urine samples.