Text-book of forensic medicine and toxicology

by R. J. M. Buchanan

Otto‘s Method.—Otto‘s modification of Stas‘s process is simpler, and at the same time equally accurate. Instead of numerous treatments and evaporations which have to be gone through in the original process, Otto converts the alkaloid into a salt, such as the sulphate, by the addition of acid, and after solution in a small quantity of water, agitates with successive quantities of ether, which remove all foreign fatty matters, leaving the solution of the alkaloid comparatively pure, and from which the alkaloid may be obtained in a state of great purity, by first rendering the solution alkaline and then using ether to dissolve the alkaloid.

R. Wagner‘s Method.—The presence of alkaloids in organic liquids—strychnia in beer, for example—may, according to R. Wagner (Zeitschr. Anal. Chem., vol. iv. p. 387), be detected by mixing the liquid, diluted with two vols. water (½ to 1 litre), with about 5 c.c. of a solution of iodine in potassium iodide (12.7 grains iodine to the litre) and a few drops of sulphuric acid. The precipitate separated from the supernatant liquid is dissolved in a dilute solution of sodium hyposulphite, and again precipitated by means of the iodine solution. If this new precipitate be now dissolved in aqueous sulphurous acid, the solution will leave, on evaporation, the pure sulphate of the base.

Dragendorff‘s Method.—This is intended for the purpose of separating alkaloids from each other when more than one are in aqueous solution, by using different solvents in sequence. Some solvents take up certain alkaloids to the exclusion of others. The process consists of extracting the aqueous acid solution of the alkaloids successively with petroleum spirit, benzene, chloroform, and amyl-alcohol, then alkalising it and repeating with the same solvents.

1. From the acid solution benzene removes caffeine, colchicine, santonin, digitalin, cantharidin. Chloroform removes papaverine, colchicine, narceine, picrotoxin.

2. From the alkaline solution petroleum ether removes strychnine, brucine, aconitine, veratrine, conine, nicotine, lobeline, emetine, and aniline. Benzene removes atropine, hyoscyamine, physostigmine, codeine, narcotine, and further quantities of strychnine, brucine, aconitine, veratrine, and emetine. Chloroform removes morphine, narceine, papaverine, strychnine, and brucine. Amyl-alcohol removes morphine, solanine, and narceine.

The Stas process cannot be recommended for the detection of opium in organic liquids, for two reasons. Firstly, that it altogether fails to indicate the presence of meconic acid; and, secondly, because morphine is almost insoluble in ether. Dragendorff recommends the use of benzole for separating the alkaloids, but in this substance morphia is nearly insoluble. It is, however, applicable to strychnine, aconitine, conine, and atropine; but for the two last, on account of their volatility, ether is preferable.

Rodger‘s and Girdwood‘s Method.—Extraction with dilute hydrochloric acid and the use of chloroform instead of ether. Chloroform is a much better solvent of most alkaloids than ether. Particularly useful for the isolation of strychnine and for most alkaloids, but there is a little danger of hydrolysis of the alkaloid in the use of a mineral acid, e.g. hyoscine.

Stevenson‘s Modification of the Otto-Stas Process.—The material to be examined, if solid, is finely divided, and digested for twenty-four hours with twice its weight of rectified spirit at 35° C.; if fluid, with twice its volume. The clear liquid is decanted and the residue again digested with fresh spirit; this is again decanted, and mixed with the first alcoholic solution. The residue is now digested with spirit faintly acidified with acetic acid; this is decanted, and the residue digested with two or three lots of unacidified alcohol. The alcoholic extracts obtained before acidification are mixed together and rapidly raised to 70° C. for a moment or two. They are quickly cooled and filtered, and the filter washed with spirit. The acidified extract and those after it are mixed and treated in the same way. The extracts are then separately evaporated at a temperature not above 35° C. to the consistency of a syrup, the excess of acid being neutralised with soda; these are extracted with absolute alcohol, and the extracts evaporated to a syrup as before. The syrupy extracts are now diluted with a small quantity of water, filtered, the filters washed with water, and the filtrates mixed. The liquid will contain the whole of the alkaloids, and will be free from albuminoids, which have been coagulated while the extracts were at 70° C. The liquid containing the alkaloids is extracted several times with washed ether, which removes fatty acids or oils, but does not remove alkaloidal salts. The ether should be washed with water to which a few drops of sulphuric acid has been added, and the water kept: this has to be done because some alkaloidal salts are slightly soluble in ether. The acid liquid and the acidified aqueous washings of the ether are mixed together, rendered alkaline with sodium carbonate, and exhausted firstly with a mixture of one volume of chloroform to three of ether, and lastly three or four times with ether alone.

The alkalisation with sodium carbonate liberates the alkaloids from their salts, and these are soluble in the chloroform-ether and ether. These ethereal extracts are then washed with water acidified with sulphuric acid, and water alone, and the washings mixed. The water acidulated with sulphuric acid converts them into sulphates, which are insoluble in the ether and chloroform, and are removed by the acidified water, while impurities are left behind. The mixed aqueous and acid extracts are again washed with ether, the ether removed, and the liquid re-alkalised with sodium carbonate and then re-extracted with chloroform-ether and ether.

The ethereal solutions are removed and are washed with water slightly alkalised with sodium carbonate. The ethereal solution is filtered through a dry filter, the filtrate evaporated to dryness first at 35° C. then at 100° C., and cooled over sulphuric acid. The residue is weighed and represents the weight of the alkaloids. A test quantity should be evaporated to see if there be any oily odorous residue, i.e. a volatile alkaloid, nicotine or conine. If so, the chloroform and ether extracts should be mixed with a little pure ether and strong hydrochloric acid; the alkaloids are thus changed into non-volatile hydrochlorides, which are left behind after evaporation of the chloroform and ether. Any alkaloid found should be converted into the hydrochloride, dissolved, and tested by special tests. Morphine cannot be extracted except in very minute amounts by this method. To obtain it, the first alkaline solution from which the other alkaloids have been removed should be extracted with acetic ether and ether, in which morphine is soluble.