A: Triturate a quantity of finely powdered Tablets,equivalent to about 100mg of guaifenesin,with 10mLof chloroform,filter,and evaporate 1mLof the filtrate on a watch glass.Mix the residue with 1drop 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 preparationcorresponds to that of the guaifenesin peak in the chromatogram of the Standard preparationas obtained in the Assay.

Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C10H14O4dissolved in filtered portions of the solution under test from UVabsorbances at the wavelength of maximum absorbance at about 274nm in comparison with a Standard solution having a known concentration of USP Guaifenesin RSin the same medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C10H14O4is dissolved in 45minutes.

Mobile phase— Prepare a suitable filtered and degassed mixture of water,methanol,and glacial acetic acid (60:40:1.5).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Benzoic acid solution— Dissolve a suitable quantity of benzoic acid in methanol to obtain a solution containing about 2mg per mL.

Resolution solution— Dissolve a suitable quantity of guaifenesin in water,with shaking,to obtain a solution containing about 2mg per mL.Transfer 2.0mLof this solution and 5.0mLof Benzoic acid solutionto a 100-mLvolumetric flask,add 40mLof methanol,dilute with water to volume,and mix to obtain a solution containing about 40µg of guaifenesin and 100µg of benzoic acid per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Guaifenesin RSquantitatively in water,with shaking,to obtain a solution having a known concentration of about 2mg per mL.Transfer 2.0mLof this solution to a 100-mLvolumetric flask,add 45mLof methanol,dilute with water to volume,and mix to obtain a Standard preparationhaving a known concentration of about 40µg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 200mg of guaifenesin,to a 100-mLvolumetric flask,add about 60mLof water,and shake for about 15minutes.Dilute with water to volume,filter if necessary to obtain a clear solution,and mix.Transfer 2.0mLof this solution to a 100-mLvolumetric flask,add 45mLof methanol,dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 276-nm detector and a 4.6-mm ×25-cm column that contains 10-µm packing L1.The flow rate is about 2mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed under Procedure:the resolution,R,between the guaifenesin and benzoic acid peaks is not less than 3.0(the relative retention times are about 0.7for guaifenesin and 1.0for benzoic acid).Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative standard deviation for replicate injections is not more than 2.5%.

Procedure— Separately inject equal volumes (about 20µL)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 guaifenesin (C10H14O4)in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Guaifenesin RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.