A new type of polarographic catalytic wave of organic compound, termed as association/parallel catalytic hydrogen wave, has been reported. The association/parallel catalytic hydrogen wave with such characters as the negative shift of the peak potential and the great increase of the peak current in midecamycin-hydrogen peroxide system was studied. Here hydrogen peroxide as ligand formed an association complex with protonated midecamycin, which caused the peak potential of the catalytic hydrogen wave of midecamycin to shift negatively. Additionally, the great increase of the peak current was due to the further catalysis of the catalytic hydrogen wave by hydroxyl radical produced in the reduction of hydrogen peroxide at electrode. It was determined that the association ratio was 1:1 and the apparent association constant was 7.18. In 0.15 mol·L^-1 KH₂PO₄-NaOH (pH 7.4)-0.02 mol·L^-1 H₂O₂ supporting electrolyte, the second-order derivative peak current of the association/parallel catalytic hydrogen wave with peak potential -1.59 V (vs. SCE) was proportional to the midecamycin concentration in the range of 2.0×10^-8～1.0×10^-5 mol·L^-1. The detection limit was 6×10^-9 mol·L^-1. The association/parallel catalytic hydrogen wave was two orders in magnitude higher than that of the corresponding catalytic hydrogen wave in analytical sensitivity.

Key words: midecamycin, hydrogen peroxide, association/parallel catalytic hydrogen wave