Membrane covered carbon paste electrode for the electrochemical determination of peroxidase and microperoxidase in a flow system

Abstract

Electrocatalytical reduction of hydrogen peroxide in a flow system was performed by horseradish peroxidase (HRP) and microperoxidase-11 (MP-11) on membrane covered modified carbon paste electrodes (MCPE). MCPE contained the mediator 1-( N, N-dimethylamine)-4-(4-morpholine)benzene (AMB) dissolved in paraffin. The electrocatalytical process proceeded at 0.0 V vs. 0.1 M NaCl Ag/AgCl. Half-time of the electrocatalytic current in flow system was dependent on enzyme and electrode type. In the case of HRP it was 2.1 and 8.5 min, respectively, for bare and membrane covered and with 1.7% of mediator modified electrode. Decreasing the AMB amount 10 times changed the half-time only a little. The kinetics of MP-11 current evolution was not limited by MP-11 transport through the membrane since the half-time change was small for bare and membrane covered electrode. The dependence of electrocatalytical current on hydrogen peroxide showed hyperbolic form at different AMB amount. The largest current for HRP and MP-11 was measured at carbon paste loading by 1.7% of mediator. Half-concentration of hydrogen peroxide changed from 0.04–0.12 mM and from 0.18 to 1.4 mM, respectively, for HRP and MP-11. In the case of HRP the largest ratio between membrane free and membrane covered MCPE current was at 0.88% of mediator loading. A leakage of AMB from membrane free MCPE was fast in the first 10 min and later stabilized. The total amount of AMB liberated from the electrode in the period of 2.5 h corresponded to 12% of the total mediator quantity in MCPE. The electrocatalytical current decreased only 16% over this period of time. The electrode covering by membrane suppressed the fast phase of mediator leakage, the total amount of liberated mediator was similar to the bare electrode, but the electrode current decreased only 5%.