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

摘要

A differential pulse polarographic method is described for the determination of 3 pharmacologically active 5-hydroxynaphthoquinones in Drosera-containing phytomedicines available on the Austrian market. The polarographic behaviours of plumbagin, 7-methyljuglone and droserone were examined in various buffer systems in the pH-range from 3.5 to 10.0. The compounds were reduced in a single reversible peak at the dropping mercury electrode. The differential pulse polarograms of the naphthoquinones showed distinct peaks in sodium acetate/acetic acid buffer:methanol solution, and a plot of peak height against concentration was found to be linear over the range 0.16-30.0μg/ml for droserone, 0.06-8.0μg/ml for plumbagin and 0.16-25.0μg/ml for 7-methyljuglone. The polarographic method was applied to determine the amounts of these naphthoquinones in 3 Drosera-containing phytomedicines. In one preparation, the droserone concentrations, depending on the sample taken, were found to be 6.81 and 5.78μg/ml, whilst in a second preparation the droserone concentrations were 1.87, 3.67 and 0.51μg/ml. The content of plumbagin and 7-methyljuglone was lower than the polarographic detection limit (0.4μg/ml of each). In a third preparation, neither droserone, plumbagin, nor 7-methyljuglone were polarographically detectable (<0.2μg/ml).