Naphthoquinone esters from the root of Rhinacanthus nasutus.

Reinvestigation of the root of Rhinacanthus nasutus afforded, in addition to rhinacanthin-A to -D reported previously, two new dimethyldihydropyranonaphthoquinone esters (5, 6) and eight new 2-hydroxy-1,4-naphthoquinone esters (7-14) were isolated. The stereochemistry of rhinacanthin-A was determined as the R configuration. Compounds rhinacanthin-G to -N, belong to a class of 2-hydroxy-3-(3-hydroxy-2,2-dimethylpropyl)-1,4-naphthoquinone esters, and so far have been isolated only in this plant. Their biosynthesis is also discussed.

Determination of lead, arsenic and mercury in cosmetic formulations at modified electrodes.

Synopsis Lead, arsenic and mercury in cosmetic formulations digested with HNO(3)+ HF (10:3) or HNO(3)+ H(2)SO(4) (5:1) in a microwave oven were determined, respectively, by the thin mercury film electrode, gold electrode and thin gold film electrode in sodium acetate buffer, in 6 m HNO(3) and 0.1 m HCIO(4) solution. Comparison with results obtained from atomic absorption spectrophotometric analysis (AAS) showed good agreement. The detection limits were 0.38 ppb (mugl(-1)), 0.66ppb and 0.04ppb for lead, arsenic and mercury, respectively, using square wave anodic stripping voltammetry. The detection limits for lead, arsenic and mercury were 0.53 ppb, 1.24ppb and 0.40ppb, respectively, using AAS. The two methods proposed were applicable to the determination of concentrations at ppb levels of commercial cosmetic formulations.