Indirect voltammetric determination of nicotinic acid by using a graphite paste electrode modified with reduced graphene oxide and a molecularly imprinted polymer

Nano-sized molecularly imprinted polymers (nano-MIPs) possessing cavities that fit nicotinic acid were synthesized via precipitation polymerization. Acrylamide, divinyl benzene, nicotinic acid (NA) and acetone were utilized as functional monomer, cross-linker, template and porogen, respectively. The nano-MIPs were placed on a graphite paste electrode doped with reduced graphene oxide (rGO). An indirect detection method was employed that makes use of Cu(II) ion as an electrochemical probe because NA itself does not generate a significant voltammetric signal. To accomplish this, the modified electrode was first incubated with a solution of nicotinic acid, then with a solution of Cu(II). It is found that a MIP-based electrode that was previously incubated with nicotinic acid solution showed a distinct signal for Cu(II), while the same electrode incubated with Cu(II) only gave a very weak signal. A non-imprinted polymer-based electrode also gave no signal. In addition, the presence of rGO in the electrode led to a significantly increased current. Various factors influencing the analytical performance were optimized. The electrode, best operated at 0.2 V (vs. Ag/AgCl), has a linear response in the 10 nM to 0.2 μM NA concentration range. The detection limit is as low as 8.0 nM (at 3 Sb/m). The method was applied to the determination of NA in spiked plasma and urine samples.