The rhizome differs from the root in having a ring of xylem around a large pith. The pericycle contains characteristic sclerenchymatous cells. Spiral vessels are found in the protoxylem. The pith is composed of pitted parenchyma, which is somewhat lignified.

Extract the alkaloids from the ether with 2 N sulfuric acid, using at first 15 mL, or more, if necessary, to ensure an acid reaction, then successive 10-mL portions until extraction is complete, and filtering all extracts through the same filter into a second separator. To the combined acid solutions add about an equal volume of ether, render the mixture distinctly alkaline with 6 N ammonium hydroxide (at least pH 10, by test paper), and extract with successive portions of ether until the last extract shows not more than a slight turbidity when treated as follows: Evaporate 1 mL of the last extraction, dissolve the residue in 0.5 mL of 0.5 N hydrochloric acid, and add 1 drop of mercuric iodide TS.

Filter each portion of the ether extract into a flask or beaker, and carefully evaporate the combined ether extracts on a steam bath almost to dryness. Add 5 mL of ether and 10.0 mL of 0.1 N sulfuric acid VS, and heat on a steam bath to dissolve the alkaloids and to remove all the ether. Cool, add 15 mL of water, then add methyl red TS, and titrate the excess acid with 0.1 N sodium hydroxide VS. Each mL of 0.1 N sulfuric acid is equivalent to 24.0 mg of the total ether-soluble alkaloids of ipecac, calculated as emetine (C29H40N2O4).

Prepare Column I as follows. To the Assay preparation add 6 g of purified siliceous earth, mix, transfer the mixture to the column, scrub the beaker with about 1 g of the purified siliceous earth, transfer this to the top of the column, and tamp. Prepare Column II using 3 g of the purified siliceous earth and 2 mL of Phosphate buffer; prepare Column III using 2 mL of Citric acid buffer and 3 g of the purified siliceous earth; and prepare Column IV using 2 mL of sodium hydroxide solution (1 in 50) and 3 g of the purified siliceous earth. Pack a pledget of glass wool on the top of each column.

Elute Column IV with 75 mL of chloroform, collecting the eluate in a 250-mL separator containing 150 mL of ether. Discard Column IV. Extract with one 20-mL and then with two 10-mL portions of 0.5 N sulfuric acid, collecting the extracts in a 50-mL volumetric flask. Rinse the stem of the separator, add the acid to volume, and mix (cephaeline solution).

Concomitantly determine the absorbances of the emetine solution, the cephaeline solution, and the Standard preparation in 1-cm cells at the wavelength of maximum absorbance at about 283 nm and at 350 nm, with a suitable spectrophotometer, using 0.5 N sulfuric acid as the blank.

Calculate the quantity, in mg, of emetine in the portion of Ipecac taken by the formula:

in which C is the concentration, in µg per mL, of emetine in the Standard preparation; and the parenthetic expressions are the differences in the absorbances of the solution of emetine from the Assay preparation (U) and the Standard preparation (S), respectively, at the wavelengths indicated by the subscripts.

Calculate the quantity, in mg, of cephaeline in the portion of Ipecac taken by the formula:

in which 0.971 is the ratio of the molecular weight of cephaeline to that of emetine; C is as defined above; and the parenthetic expressions are the differences in the absorbances of the solution of cephaeline from the Assay preparation (U) and the Standard preparation (S), respectively, at the wavelengths indicated by the subscripts.