A: Triturate a portion of the contents of Capsules, equivalent to about 100 mg of guaifenesin, with 10 mL of chloroform, filter, and evaporate 1 mL of the filtrate on a watch glass. Mix the residue with 1 drop of formaldehyde and a few drops of sulfuric acid: a deep cherry-red to purple color is produced.

B: The retention time of the guaifenesin peak in the chromatogram of the Assay preparation corresponds to that of the guaifenesin peak in the chromatogram of the Standard preparation as obtained in the Assay.

Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C10H14O4 dissolved, employing the procedure set forth in the Assay, making any necessary modifications.

Tolerances— Not less than 75% (Q) of the labeled amount of C10H14O4 is dissolved in 45 minutes.

Mobile phase, Benzoic acid solution, Resolution solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Guaifenesin Tablets.

Assay preparation— Transfer, as completely as possible, the contents of not less than 20 Capsules to a suitable tared container, and determine the average content weight per Capsule. Mix the combined contents, and transfer an accurately weighed portion, equivalent to about 200 mg of guaifenesin, to a 100-mL volumetric flask. Proceed as directed for Assay preparation in the Assay under Guaifenesin Tablets, beginning with “add about 60 mL of water.”

Procedure— Proceed as directed for Procedure in the Assay under Guaifenesin Tablets. Calculate the quantity, in mg, of guaifenesin (C10H14O4) in the portion of Capsule contents taken by the formula: in which the terms are as defined therein.