Spectrophotometric determination of quinine, emethine and ephedrine in pharmaceutical preparations with tetrabromophenolphthalein ethyl ester by solvent extraction.

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Abstract
A singly charged tetrabromophenolphthalein ethyl ester (TBPE) anion was extracted with alkaloids as 1:1 complexes in 1,2-dichloroethane. Of various solvents, a TBPE-1,2-dichloroethane system gave a red color for alkaloids, while in the absence of alkaloids, an organic phase is pale yellow color. Spectrophotometric methods were investigated for the determination of a small amount of the alkaloids, such as quinine, emethine and ephedrine, by solvent extraction. Quinine is determined by measuring the absorbance of the extracts over a range from 0.5-5 .times. 10-6 M (0.20-1.98 .mu.g/ml) at 555 nm. Emethine is determined from 2 .times. 10-6 M to 1 .times. 10-5 M (1.1-5.5 .mu.g/ml) at 570 nm and ephedrine, from 1 .times. 10-6 M to 1 .times. 10-5 M (0.20-2.0 .mu.g/ml) at 555 nm. From the conductivity measurements, the red species in the extract is considered to be a kind of charge transfer complexes.

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