Evaluation of the number of carboxyl groups on glassy carbon after modification by 3,4-dihydroxybenzylamine

An electrochemical method for determining the number of carboxyl groups on glassy carbon (GC) has been developed. In this method, a carboxyl group is modified with 3,4-dihydroxybenzylamine (DHBA) by the action of carbodiimide. The number of carboxyl groups can be determined from the peak area of DHBA in cyclic voltammograms of GC. The physical adsorption of DHBA on GC is not desirable for this quantification. Thus, physical adsorption is minimized by thorough washing and optimization of the modification conditions. Physical adsorption was assessed by experiments on DHBA-treatment without carbodiimide. The minimization and assessment of the physical adsorption of DHBA enables the use of this modification to determine the number of carboxyl groups on GC. The method is quantitative and much more rapid than other methods that have been used to evaluate surface oxides. Using this method, the numbers of carboxyl groups on several electrochemically oxidized GCs were determined. The results revealed that strong electrochemical oxidation of GC increases not only the total number of carboxyl groups but also the surface area of the GC. Strong oxidation does not greatly increase the number of carboxyl groups per surface area.