Rodgers and Girdwood’s Method
This method—which as yet has only been employed in the detection of strychnine—is based upon the solubility of this alkaloid in chloroform. The substances under examination are digested with dilute hydrochloric acid, and the mixture filtered. The filtrate is then evaporated to dryness on the water-bath, the residue taken up with pure alcohol, the alcoholic solution evaporated, the second residue treated with water, and the solution so obtained filtered. The filtrate is next supersaturated with ammonia, and well shaken with chloroform, which, upon being separated by means of a pipette and evaporated, leaves the alkaloid in an impure state. Concentrated sulphuric acid is then poured upon the alkaloid: the latter is not affected by this treatment, whereas the foreign organic substances present are carbonized. After the lapse of several hours, the mixture is treated with water, the fluid filtered, and the strychnine extracted from the filtrate by means of ammonia and chloroform, as already described. The operation is repeated until the residue obtained by evaporating the chloroform is no longer affected by the treatment with sulphuric acid.