A: Injection meets the requirements for Identification test A under Digoxin Oral Solution.

B: Chloramine T–trichloroacetic acid reagent, Spotting solvent, and Standard solution—Proceed as directed for Identification test B under Digoxin Oral Solution.

Test solution— Pipet a volume of Injection, equivalent to 0.5 mg of digoxin, into a separator, and add 5 mL of water. Extract with three 10-mL portions of chloroform, combining the extracts in a conical flask. Evaporate the combined chloroform extracts on a steam bath with the aid of a current of air to dryness. (If traces of water or propylene glycol remain, dry the flask in vacuum at 100 for 30 minutes.) Dissolve the residue in 2 mL of Spotting solvent.

Procedure— Proceed as directed for Procedure in the test for Related glycosides under Digoxin, except to omit the use of the Gitoxin standard solution. Examine the plate under long-wavelength UV light: the RF value of the principal spot in the chromatogram of the Test solution corresponds to that of the Standard solution.

Mobile phase— Proceed as directed in the Assay under Digoxin.

Standard preparation— Dissolve an accurately weighed quantity of USP Digoxin RS in diluted alcohol, and dilute quantitatively with diluted alcohol to obtain a solution having a known concentration of about 250 µg per mL. Use a sonic bath to aid dissolution. If necessary, dilute quantitatively to match, approximately, the concentration of the Injection.

Chromatographic system and System suitability preparation— Proceed as directed in the Assay under Digoxin.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and Injection into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in µg, of C41H64O14 in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of USP Digoxin RS in the Standard preparation; and rU and rS are the responses for the digoxin peaks obtained from the Injection and the Standard preparation, respectively.