Packaging and storage— Preserve in tight containers.

USP Reference standards 11—
USP Chlorothiazide RS.

Identification— The UV absorption spectrum of the solution of chlorothiazide prepared from Oral Suspension as directed in the Assay exhibits maxima and minima at the same wavelengths as that of a solution of USP Chlorothiazide RS, prepared as directed in the Assay, concomitantly measured.

Uniformity of dosage units 905—

Deliverable volume 698—

pH 791: between 3.2 and 4.0.

Assay— Transfer to a 250-mL volumetric flask an accurately measured volume of Oral Suspension, equivalent to about 250 mg of chlorothiazide, dilute with sodium hydroxide solution (1 in 250) to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, add dilute hydrochloric acid (1 in 100) to volume, and mix. Transfer 50.0 mL of the resulting solution to a 125-mL separator, and wash with two 25-mL portions of chloroform, discarding the washings. Transfer 10.0 mL of the washed solution to a 100-mL volumetric flask, dilute with sodium hydroxide solution (1 in 250) to volume, and mix. Dissolve an accurately weighed quantity of USP Chlorothiazide RS in sodium hydroxide solution (1 in 250) 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 292 nm, with a suitable spectrophotometer, using sodium hydroxide solution (1 in 250) as the blank. Calculate the quantity, in mg, of chlorothiazide (C7H6ClN3O4S2) in each mL of the Oral Suspension taken by the formula: in which C is the concentration, in µg per mL, of USP Chlorothiazide RS in the Standard solution; V is the volume, in mL, of Oral Suspension taken; and AU and AS are the absorbances of the solution from the Oral Suspension and the Standard solution, respectively.

Topic/Question	Contact	Expert Committee
Monograph	Sujatha Ramakrishna, Ph.D. Scientist 1-301-816-8349	(MDCV05) Monograph Development-Cardiovascular
Reference Standards	Lili Wang, Technical Services Scientist 1-301-816-8129 RSTech@usp.org

USP32–NF27 Page 1905