Carbon paste electrode (CPE) was first reported in 1958 by Adams. It has become widely used in electrochemical research due to its often-cited advantages of low ohmic resistance, large potential window, and ease of modification. Ease of modification is one of the most valuable features of CPE. This is due to the well-developed surface of CPE, which has a high adsorptivity for substances. To a large extent, it enhanced
the sensitivity and selectivity of CPE. Beitollahi et al. introduced two methods of the simultaneous determination of UA and FA that applied carbon nanotube modified carbon paste electrode as a working electrode. However, one required the more expensive carbon nanotube and dioxo-molybdenum (VI) complex [Mo(C10H11NO2)O2(CH3OH)] synthesized in the laboratory as the material of modified electrode. The other needed synthesize 5-amino-3,4-dimethoxy-biphenyl-2-ol (5ADMB) in addition to carbon nanotube to modify the carbon paste electrode. What is more, the preparation of 5ADMB was cumbersome and adopted Pd(PPh3)4 as the catalyst. The progress of reaction was heated at about 90 ◦C for at least 12 h and monitored by TLC. The crude product needed to be further recrystallized to afford pure 5ADMB. Ardakani et al. reported the electrocatalytic and simultaneous determination of UA and FA by using a 2,2-[1,2 buthanediylbis(nit-riloethylidyne)]-bis hydroquinone (BQ)/TiO2 nanoparticles modified carbon paste electrode (BQTMCPE). But the synthesis of BQ was a complicated procedure
and it took 10 h or more to prepare TiO2 nanoparticles. While, the simultaneous determination of UA and FA was also achieved at the
chloranil modified carbon nanotube paste electrode (CAMCNPE). Thus it can be seen that the above modified electrodes used to determine UA and FA are all composite materials. Obviously, the disadvantages of corresponding electrodes are high cost, numerous of process, longer reaction time. In particular, these electrodes use some harmful organic reagents, for example, chloroform and chloranil. Therefore, these modified electrodes will not obtain the widespread popularization and application in routine laboratories.