A:Infrared Absorption á197Kñ.

B: Transfer about 50mg of it to a 500-mLvolumetric flask,add water to volume,and mix.Transfer 10.0mLof the resulting solution to a 100-mLvolumetric flask,add 2.0mLof 0.1Nhydrochloric acid,dilute with water to volume,and mix to obtain a 1in 100,000solution:the UVabsorption spectrum of the solution so obtained exhibits maxima and minima only at the same wavelengths as that of a similar solution of USP Isoniazid RS,concomitantly measured.

Mobile phase— Dissolve 4.4g of docusate sodium in 600mLof methanol,add 400mLof water,adjust with 2Nsulfuric acid to a pHof 2.5,and mix.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Isoniazid RSin Mobile phase,and quantitatively dilute with Mobile phaseto obtain a solution having a known concentration of about 0.32mg per mL.

Assay preparation— Transfer about 16mg of Isoniazid,accurately weighed,to a 50-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency determined from the isoniazid peak is not less than 1800theoretical plates;the tailing factor for the isoniazid peak is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C6H7N3Oin the portion of Isoniazid taken by the formula: in which Cis the concentration,in mg per mL,of USP Isoniazid RSin the Standard preparation;and rUand rSare the peak responses of isoniazid obtained from the Assay preparationand the Standard preparation,respectively.