A: Infrared Absorption 197K.

B: Transfer about 50 mg of it to a 500-mL volumetric flask, add water to volume, and mix. Transfer 10.0 mL of the resulting solution to a 100-mL volumetric flask, add 2.0 mL of 0.1 N hydrochloric acid, dilute with water to volume, and mix to obtain a 1 in 100,000 solution: the UV absorption 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.

(Official January 1, 2007)

Mobile phase— Dissolve 4.4 g of docusate sodium in 600 mL of methanol, add 400 mL of water, adjust with 2 N sulfuric acid to a pH of 2.5, and mix. Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)— 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 1.5 mL per 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 1800 theoretical 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C6H7N3O in the portion of Isoniazid taken by the formula: in which C is the concentration, in mg per mL, of USP Isoniazid RS in the Standard preparation; and rU and rS are the peak responses of isoniazid obtained from the Assay preparation and the Standard preparation, respectively.