Determination of 5-hydroxynaphthoquinones in phytotherapeutic Drosera preparations by differential pulse polarography

A differential pulse polarographic method is described for the determinatio n of three pharmacologically active 5-hydroxynaphthoquinones in Drosera-con taining phytomedicines available on the Austrian market. The polarographic behaviours of plumbagin, 7-methyljuglone and droserone were examined in var ious buffer systems in the pH-range from 3.5 to 10.0. The compounds were re duced in a single reversible peak at the dropping mercury electrode. The di fferential pulse polarograms of the naphthoquinones showed distinct peaks i n sodium acetate/acetic acid buffer:methanol solution, and a plot of peak h eight against concentration was found to foe linear over the range 0.16-30. 0 mu g/ml for droserone, 0.06-8.0 mu g/ml for plumbagin and 0.15-25.0 mu g/ ml for 7-methyljuglone, The polarographic method was applied to determine t he amounts of these naphthoquinones in three Drosera-containing phytomedici nes, In one preparation the droserone concentrations, depending on the samp le taken, were found to be 6.81 and 5.78 mu g/ml, whilst in a second prepar ation the droserone concentrations were 1.87, 3.67 and 0.51 mu g/ml. The co ntent of plumbagin and 7-methyljuglone was lower than the polarographic det ection limit (0.4 mu g/ml of each). In a third preparation neither droseron e, plumbagin, nor 7-methyljuglone were polarographically detectable (<0.2 m u g/ml). Copyright (C) 1999 John Wiley & Sons, Ltd.