Polarographic determination of berberine in the presence of H(2)O(2) in medicinal plants.

The mechanism of the parallel catalytic wave of berberine in the presence of H(2)O(2) was studied. The results showed that the reduction process of the C[double bond]N bond of berberine was two successive one-electron transfers, in which an intermediate free radical was involved. When H(2)O(2) was present, it oxidized the free radical to the original C[double bond]N bond, producing the parallel catalytic wave of berberine. In Na(2)B(4)O(7)-Na(2)CO(3) (pH 9.4, 0.08 M)-H(2)O(2)(4 mM) supporting electrolyte, the peak current of the catalytic wave was linear to the berberine concentration in the range of 1.0 x 10(-8)-3.0 x 10(-7) M. The limit of detection was 7.0 x 10(-9) M. The catalytic wave can be applied to direct determination of berberine in medicinal plant Coptis chinensis Franch, after sufficiently diluting the water extraction without preliminary separation.