Abstract
The need to measure the amount of cocaine penetrating to the aqueous humor of an experimental animal after instillation of a cocaine solution into the conjunctival sac led to the following analytical procedure, which we find applicable to the quantitation of traces of many alkaloids in aqueous solution, and of certain alkaloids, particularly cocaine and strychnine, in body fluids. The method, which is accurate within the limits of colorimetric observations, is strikingly simple, and we believe will be of interest to workers in pharmacology, toxicology and experimental medicine.
A. Procedure for aqueous solutions. To a measured amount of solution containing from .5 to .05 mg. of the alkaloid is added 1 cc. of a 1% solution of phosphomolybdic acid in normal sulphuric acid. This is best done in a small test tube of about 5 cc. capacity. After mixing and standing for 15 minutes, the mixture in the test tube is centrifuged and the supernatant fluid decanted. The residue is resuspended in water, again centrifuged and the supernatant discarded. To the washed precipitate is now added 1 cc. of fifth normal sulphuric acid, 1 cc. of 2% aqueous solution of hydroquinone, and after shaking, 1 cc. of the carbonate-sulphite solution used in the Bell and Doisy 1 method for phosphate determination (15% sodium carbonate and 3% sodium sulphite). The color developed is read promptly in the small Duboscq type colorimeter against a standard prepared by treating 1 cc. of a solution of known and approximately equal alkaloid content (using the same alkaloid that is being determined) simultaneously with the same reagents. If necessary, it is a relatively simple matter to prepare several standards (5 of the small test tubes can be spun in an ordinary 50 cc. metal centrifuge cup) and the proper one can be selected by inspection.
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