Standard solutions— Dissolve a quantity of USP Butabarbital RS in a mixture of chloroform and methanol (1:1) to obtain a solution having a concentration of 4.0 mg per mL (Standard solution A). Dilute 1.0 mL of Standard solution A with a mixture of chloroform and methanol (1:1) to 10.0 mL, and mix (Standard solution B).

Test solution— Dissolve a quantity of Butabarbital in a mixture of chloroform and methanol (1:1) to obtain a solution having a concentration of 40 mg per mL.

Procedure— Proceed as directed for Procedure in the test for Chromatographic purity under Butabarbital Sodium.

Internal standard solution— Transfer about 400 mg of tetracosane to a 200-mL volumetric flask, add chloroform to volume, and mix.

Standard preparation— Transfer about 200 mg of USP Butabarbital RS, accurately weighed, to a 100-mL volumetric flask, add chloroform to volume, and mix. Transfer 10.0 mL of the resulting solution to a 50-mL volumetric flask, add 10.0 mL of Internal standard solution, and mix to obtain a solution having a known concentration of about 1.0 mg of USP Butabarbital RS per mL.

Assay preparation— Transfer about 200 mg of Butabarbital, accurately weighed, to a 100-mL volumetric flask, add chloroform to volume, and mix. Transfer 10.0 mL of the resulting solution to a 50-mL volumetric flask, add 10.0 mL of Internal standard solution, and mix.

Chromatographic system (see Chromatography 621)—The gas chromatograph is equipped with a flame-ionization detector and a 4-mm × 1.8-m column packed with 10% phase G37 on support S1AB. The column temperature is maintained at about 260, the injection port at about 260, and the detector block at about 300. Dry nitrogen is used as the carrier gas at a flow rate of about 50 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factors for the analyte and internal standard peaks are not more than 1.3 and 1.2, respectively; the resolution, R, between the analyte and internal standard peaks is not less than 3.0; and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 2 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.6 for butabarbital and 1.0 for tetracosane. Calculate the quantity, in mg, of C10H16N2O3 in the portion of Butabarbital taken by the formula: in which C is the concentration, in mg per mL, of USP Butabarbital RS in the Standard preparation; and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.