Electrochemically preanodized clay-modified electrodes were used for the detection of uric acid or dopamine in the presence of a high concentration of ascorbic acid by square wave voltammetry. The major obstacle of the overlapped oxidation potential of ascorbic acid could be overcome through the distinct ability of uric acid and dopamine to coordinate with the electrochemically preanodized clay-modified electrodes. The selective sensing of dopamine is further improved by the charge-exclusion and preconcentration features of Nafion. Linear calibration curves are obtained for 0.5-10 and 10-100 µM uric acid with 30 s preconcentration time in 0.1 M, pH 1.0 citrate buffer and for 0-6 µM dopamine in 0.1 M, pH 7.4 phosphate buffer with 20 s preconcentration time. The detection limits (3σ) are 0.2 µM and 2.7 nM for uric acid and dopamine, respectively. The practical analytical utility is illustrated by selective measurements of uric acid in human urine without any preliminary treatment.

Considering the unique adsorption and regeneration properties of dopamine, glucose oxidase, and nontronite, a glucose sensor was constructed by immobilizing glucose oxidase and nontronite clay coating on a glassy carbon electode with dopamine as mediator. The response of the glucose sensor was determined by measuring the cyclic voltammetric oxidation peak current values of dopamine under aerobic solution conditions. The effects of the amount of enzyme immobilized, the operating pH, and the common interferences on the response of the glucose sensor were studied. The detection limit was 7.4 µM (S/N ) 3), with a linear range extending to about 10 mM, giving a dynamic range of about 3 orders of magnitude for 0.8 mM dopamine. When stored in pH 7 phosphate buffer at 4 °C, the sensor shows almost no change in performance after operating for 45 days.

Electrochemically preanodized nontronite clay-modified electrodes were found to be very sensitive in the detection of dopamine and catechol by square-wave voltammetry. When preanodized in a neutral medium at þ1.8 V (vs. Ag/AgCl) for 60 s, the clay-modified electrodes exhibit a marked enhancement of the current response for dopamine and catechol. The sensitivity of dopamine can be further improved at the preanodized claymodified electrode with the addition of triethylamine. After 20 s preconcentration in phosphate buffer (pH 7.4) solution, linear calibration plots are obtained over 0-0.7 mM and 0.7-15 mM ranges with a detection limit (3j) of 0.10 nM for catechol. As to dopamine, in the presence of 30 mM triethylamine, linear calibration plots are obtained over 0-1 mM and 1-10 mM ranges and the detection limit is 0.056 nM.

Electrochemically preanodized nontronite clay‐modified electrodes were found to be very sensitive in the detection of dopamine and catechol by square‐wave voltammetry. When preanodized in a neutral medium at +1.8 V (vs. Ag/AgCl) for 60 s, the clay‐modified electrodes exhibit a marked enhancement of the current response for dopamine and catechol. The sensitivity of dopamine can be further improved at the preanodized clay‐modified electrode with the addition of triethylamine. After 20 s preconcentration in phosphate buffer (pH 7.4) solution, linear calibration plots are obtained over 0–0.7 μM and 0.7–15 μM ranges with a detection limit (3σ) of 0.10 nM for catechol. As to dopamine, in the presence of 30 μM triethylamine, linear calibration plots are obtained over 0–1 μM and 1–10 μM ranges and the detection limit is 0.056 nM.