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

✍ Scribed by Astrid Michelitsch; Mario Wurglics; Manfred Schubert-Zsilavecz; Werner Likussar

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 75 KB
• Volume: 10
• Category: Article
• ISSN: 0958-0344
• DOI: 10.1002/(sici)1099-1565(199903/04)10:2<64::aid-pca434>3.0.co;2-t

✦ Synopsis

A differential pulse polarographic method is described for the determination of three 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 0.16-30.0 mg/ml for droserone, 0.06-8.0 mg/ml for plumbagin and 0.16-25.0 mg/ml for 7-methyljuglone. The polarographic method was applied to determine the amounts of these naphthoquinones in three Drosera-containing phytomedicines. In one preparation the droserone concentrations, depending on the sample taken, were found to be 6.81 and 5.78 mg/ml, whilst in a second preparation the droserone concentrations were 1.87, 3.67 and 0.51 mg/ml. The content of plumbagin and 7-methyljuglone was lower than the polarographic detection limit (0.4 mg/ml of each). In a third preparation neither droserone, plumbagin, nor 7-methyljuglone were polarographically detectable (`0.2 mg/ml).