Improved Solid-Contact Nitrate Ion Selective Electrodes Based on Multi-Walled Carbon Nanotubes (MWCNTs) as an Ion-to-Electron Transducer.

Possible improvement of the performance characteristics, reliability and selectivity of solid-contact nitrate ion-selective electrodes (ISE) (SC/NO3--ISE) is attained by the application of a nitron-nitrate (Nit(+)/NO3-) ion association complex and inserting multi-walled carbon nanotubes (MWCNTs) as an ion-to-electron transducer between the ion sensing membrane (ISM) and the electronic conductor glassy carbon (GC) substrate. The potentiometric performance of the proposed electrode revealed a Nernstian slope -55.1 +/- 2.1 (r(2) = 0.997) mV/decade in the range from 8.0 x 10(-8)-1 x 10(-2) M with a detection limit of 2.8 x 10(-8) (1.7 ng/mL). Selectivity, repeatability and reproducibility of the proposed sensors were considerably improved as compared to the coated disc electrode (GC/NO3--ISE) without insertion of a MWCNT layer. Short-term potential stability and capacitance of the proposed sensors were tested using a current-reversal chronopotentiometric technique. The potential drift in presence of a MWCNT layer decreased from 167 mu Vs(-1) (i.e., in absence of MWCNTs) to 16.6 mu Vs(-1). In addition, the capacitance was enhanced from 5.99 mu F (in absence of MWCNTs) to 60.3 mu F (in the presence of MWCNTs). The presented electrodes were successfully applied for nitrate determination in real samples with good accuracy.