INVESTIGATION ON DIFFERENTIAL PULSE POLAROGRAPHY V. THE POLAROGRAPHIC CURRENT OF (一) ADENOSINE-5′-MONOPHOSPHATE ON DROPPING MERCURY ELECTRODE

This paper reports the experimental results of the differential pulse polaro- graphic current of(-)adenosine-5'-monophosphate (5'-AMP) on dropping mercury electrode and the relevant theory. Tests are carried out in a 0.1M HOAc-NaOAc buffer solution (pH=4.2) and the experimental results indicate that (1) the electrode reaction is a four successive 1e-1 H~+ polarographic reversible process, (2) the polarographic current (i_T) is the sum of two components, one is the diffusion current (i_(diff)) and the other is the adsorptive current (i_(ads)). Thus the following relationship holds: i_T=xi_(ads)+(1-x)i_(diff) in which the fraction, x, can range from zero to unity. The equation for the i-E curve is as follows: where ψ=(θ_1-θ_2)/(1+θ_1)(1+θ_2); θ_1=exp((nF)/(RT))(E_1-E~0) θ_2=exp((nF)/(RT))(E_1-E~0+ΔE); C_0~* is the bulk concentration of 5'-AMP, while a is related to x by the following equation x=α/(0.858+0.142α) When α=1, the current is controlled by adsorption of the depolarizer and when α=0, the current is controlled by the rate of diffusion. The α values have been determined experimentally by the relationship between the peak current of polarographic wave and the pulse amplitude (ΔE). The values of z calculated were 0.323 (at 25℃) and 0.365 (at 7℃). The diffusion coefficient value (D_0) of 5~-AMP determined agreed with that obtained by the d. e. polarographic method reported in literature. This proves that the above equation for i_T is correct.