Sensitive and stable amperometric measurements at ionic liquid–carbon paste microelectrodes

Ionic liquids (ILs) were utilized in preparing carbon paste electrodes with improved sensitivity, linearity, and stability. In order to overcome the large capacitance encountered with these pastes which affects the measured signal, microelectrodes were used to minimize the background current and improve the signal to background response. A number of ILs were tested including those having the same anions, such as butyl, hexyl, and octyl hexafluorophosphate (PF6), and those having the same cation, including hexyl-imide, trifluorophosphate (PF3) and PF6. Based on the structure of each ILs, different responses were obtained. Several probes were utilized for those studies including hydrogen peroxide, acetaminophen, and ascorbic acid. The butyl-methyl-imidazolium (BMI)-PF6 displayed the highest response among other ILs with similar anions and the smallest peak separation. The optimum ILs loading in terms of electrode resistance, capacitance, and peak separation was 30–40%. Improved resistance to surface fouling was observed at the ILs–carbon paste electrode compared to that using mineral oil when tested for NADH detection. Very good linearity up to 1 mM hydrazine (correlation coefficient 0.996) was obtained using the ILs–carbon paste electrode.