Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Standard preparation— Dissolve an accurately weighed quantity of USP Pentobarbital RS in freshly prepared dilute ammonium hydroxide (1 in 20) to obtain a solution having a known concentration of about 10 µg of pentobarbital per mL. The concentration of pentobarbital, multiplied by 1.097, represents the equivalent amount of pentobarbital sodium.

Procedure— Determine the amount of C11H17N2NaO3 dissolved from UV absorbances at the wavelength of maximum absorbance at about 240 nm on filtered portions of the solution under test, suitably diluted with freshly prepared dilute ammonium hydroxide (1 in 20), in comparison with the Standard preparation.

Tolerances— Not less than 75% (Q) of the labeled amount of C11H17N2NaO3 is dissolved in 45 minutes.

Procedure for content uniformity— Transfer the contents of 1 Capsule to a 250-mL volumetric flask, with the aid of about 5 mL of alcohol. Add 10 mL of freshly prepared dilute ammonium hydroxide (1 in 200), and without delay dilute with the same solution to volume. Mix, filter if necessary, and discard the first 20 mL of the filtrate. Dilute a portion of the clear solution with dilute ammonium hydroxide (1 in 200) to obtain a solution having a concentration of about 10 µg of pentobarbital sodium per mL. Dissolve a suitable quantity of USP Pentobarbital RS in dilute ammonium hydroxide (1 in 200) to obtain a Standard solution having a known concentration of about 10 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 240 nm, with a suitable spectrophotometer, using dilute ammonium hydroxide (1 in 200) as the blank. Calculate the quantity, in mg, of C11H17N2NaO3 in the Capsule taken by the formula: in which T is the labeled quantity, in mg, of pentobarbital sodium in the Capsule, CU is the concentration, in µg per mL, of pentobarbital sodium in the solution from the Capsule contents, on the basis of the labeled quantity per Capsule and the extent of dilution, CS is the concentration, in µg per mL, of USP Pentobarbital RS in the Standard solution, and AU and AS are the absorbances of the solution from the Capsule contents and the Standard solution, respectively.

Internal standard— n-Tricosane.

Internal standard solution— Dissolve an accurately weighed quantity of n-tricosane in chloroform, and quantitatively dilute with chloroform to obtain a solution having a known concentration of about 0.4 mg per mL.

Standard preparation— Dissolve accurately weighed quantities of USP Pentobarbital RS and n-tricosane in chloroform, and quantitatively dilute with chloroform to obtain a solution that contains, in each mL, known amounts of about 0.9 mg of USP Pentobarbital RS and about 0.4 mg of n-tricosane.

Assay preparation— Weigh not less than 20 Capsules, and transfer the contents as completely as possible to a suitable container. Remove any residual powder from the empty capsules with the aid of a current of air, and weigh the capsule shells, determining the weight of the contents by difference. Mix the contents of the Capsules, transfer an accurately weighed portion of the powder, equivalent to about 50 mg of pentobarbital sodium, to a separator. Add 15 mL of water and 1 mL of hydrochloric acid, and extract with five 25-mL portions of chloroform. Filter the extracts through about 15 g of anhydrous sodium sulfate that is supported on a funnel by a small pledget of glass wool. Collect the combined filtrate in a 100-mL volumetric flask, wash the sodium sulfate with 15 mL of chloroform, collecting the washing with the filtrate, dilute with chloroform to volume, and mix. Combine 2.0 mL of this solution with 1.0 mL of Internal standard solution in a suitable container, and reduce the volume to about 1 mL by evaporation, with the aid of a stream of dry nitrogen, at room temperature.

Chromatographic system and System suitability— Proceed as directed for Chromatographic System and System Suitability under Barbiturate Assay 361, the resolution, R, between pentobarbital and n-tricosane being not less than 2.3. [note—Relative retention times are, approximately, 0.5 for n-tricosane barbital and 1.0 for pentobarbital.]

Procedure— Proceed as directed for Procedure under Barbiturate Assay 361. Calculate the quantity, in mg, of C11H17N2NaO3 in the portion of Capsules taken by the formula: in which 248.25 and 226.27 are the molecular weights of pentobarbital sodium and pentobarbital, respectively.