Standard solutions— Dissolve a quantity of USP Butabarbital RSin a mixture of chloroform and methanol (1:1)to obtain a solution having a concentration of 4.0mg per mL(Standard solution A).Dilute 1.0mLof Standard solution Awith a mixture of chloroform and methanol (1:1)to 10.0mL,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 40mg per mL.

Procedure— Proceed as directed for Procedurein the test for Chromatographic purityunder Butabarbital Sodium.

Solvent— Use dimethyl sulfoxide.

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

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

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

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 4-mm ×1.8-m column packed with 10%phase G37on 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 50mLper 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 1.3and 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 2µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.6for butabarbital and 1.0for tetracosane.Calculate the quantity,in mg,of C10H16N2O3in the portion of Butabarbital taken by the formula: in which Cis the concentration,in mg per mL,of USP Butabarbital RSin the Standard preparation;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.