Atropine in Belladonna Preparations

Leroy and Nicolas (1987) analyzed atropine in a powder and tincture of Belladonna, and in multicomponent tablets containing Belladonna. The sample was first dissolved in dilute sulfuric acid and washed with diethyl ether, the aqueous phase was made alkaline (pH 9-11) and the alkaloids were extracted with dichlormethane. Finally, the organic phase was evaporated and the residue was redissolved in acetonitrile. 

Because the oxidizable group in atropine is a tertiary nitrogen atom (pKa 9.8), the response increased as the pH of the mobile phase was increased. A buffer of pH 7.2 was chosen, as it offered a high response and ensured column stability. Atropine and scopolamine were separated on a hydrophilic-diol column. Reversed-phase columns were also tested, but gave long retention times. However, scopolamine was not completely resolved from the early eluting interferences on the diol column and only atropine was quantitated. 

The operating potential was chosen near the upper plateau of the voltammogram, since this offered the best compromise between a high response and a low background current (+1.2 V vs. SCE, saturated calomel electrode, similar to +1.2 V vs. Ag/AgCl). The structurally related alkaloids scopolamine arid apoatropine were also oxidized at this potential. The lower limit of the linear dynamic range was 2.9 ng for atropine. EC offered at least a tenfold lower detection limit and wider linear response than UV at 220 nm. 

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