Abstract
We undertook to learn whether quinin could be determined quantitatively in extracts of animal tissues by means of the so-called thalleioquin color reaction, but it soon became apparent that the intensity of the color varies with too many factors to permit of its use for this purpose. It was observed, however, that the color of the bromin water disappeared sharply on the addition of a slight excess of quinin, and the present method depends upon the fact that when quinin is added to bromin they combine in definite proportions with the loss of the color of the bromin in reflected light.
Hart 1 attempted unsuccessfully to estimate quinin quantitatively by means of the thalleioquin reaction. He found, however, that four atoms of bromin are absorbed by the quinin, two of them loosely. He says, “It follows, then, that quinine may be determined from its bromine absorption for five minutes in the manner stated: 1 cc. N/10 Br. = 0.0081 g. quinine.” This method has not been employed hitherto so far as we know.
Nine solutions of quinin, varying widely in concentration and containing from 0.5 to 2.0 milligrams of quinin base, were prepared by one of us (H) and examined by the other (W), who did not know the strength of the solution in any case. The determinations were made with an average error of about five per cent.
The necessary reagents are prepared in the following manner: Bromin water: Place a convenient volume of bromin in a bottle with a tightly fitting glass stopper, add water, and shake until saturation occurs with an excess of bromin in the bottom of the bottle. It keeps indefinitely.
Diluted bromin water : Dilute a convenient volume of bromin water with nine volumes of water immediately before using.
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