Voltammetric determination of uric acid with a glassy carbon electrode coated by paste of multiwalled carbon nanotubes and ionic liquid

The voltammetric behavior of uric acid (UA) has been studied at a multiwalled carbon nanotube-ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) paste coated glassy carbon electrode (MWNTsBMIMPF6/GC). It is found that UA can effectively accumulate at this electrode and cause a sensitive anodic peak at about 0.49 V (vs. SCE) in pH 4:0 phosphate buffer solutions. Experimental parameters influencing the response of the electrode, such as solution pH and accumulation time, are optimized for uric acid determination. Under the optimum conditions, the anodic peak current is linear to UA concentration in the range of 1.0 X 10(-8) M to 1.0 X 10(-6) M and 2.0 x 10(-6) M to 2.0 x 10(-5) M. The detection limit is 5.0 x 10(-9) M for 180 s accumulation on open circuit. The electrode can be regenerated by successively cycling in a blank solution for about 3 min and exhibits good reproducibility. A 1.0 X 10(-6) M UA solution is measured for eight times using the same electrode regenerated after every determination, and the relative standard deviation (RSD) of the peak current is 3.2%. As for different electrodes fabricated by the same way the RSD (i.e., the electrode to electrode deviation) is 4.2% (n = 9). This method has been applied to the determination of UA in human urine samples, and the recoveries are 99%-100.6%. In addition, comparison is made between MWNTs-BMIMPF6/GC and MWNTs/GC. Results show that the MWNTsBMIMPF6/GC exhibits higher sensitivity, selectivity and ratio of peak current to background current.