Determination of Hypericin in herbal medicine products by differential pulse polarography

A differential pulse polarographic method is presented for the determinatio n of total hypericin in phytotherapeutic preparations (drops, tablets and c apsules). The polarographic behaviours of hypericin and of pseudohypericin were examined in various buffer systems over the pH range 3.5-10.0. In Brit ton Robinson buffer:methanol solution (at pH 6.0) the differential pulse po larograms exhibited reproducible peaks at E-p-1.02 V vs silver/silver chlor ide for hypericin, and at -1.00 V for pseudohypericin, Under these conditio ns, a plot of peak height against concentration of hypericin was found to b e linear over the range 0.5-9.0 mu g/mL (r = 0.9994) and 9.0-16.0 mu g/mL ( r = 0.9987). The polarographic method was applied to the determination of t he content of total hypericin (hypericin, pseudohypericin, protohypericin a nd protopseudohypericin) in herbal medicinal products containing Hypericum perforatum. The precursors protohypericin and protopseudohypericin were con verted into hypericin and pseudohypericin, respectively, by subjecting them to artificial light or daylight prior to analysis. Under these conditions, no separation step was required for the polarographic analysis. In order t o evaluate the total concentration of hypericin, the standard addition meth od with hypericin as standard was applied, The relative standard deviation involved in analysing various herbal medicinal products ranged from +/-1.9 to 2.9%. Copyright (C) 2000 John Wiley & Sons, Ltd.