A: Infrared Absorption á197Mñ.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of theStandard preparation,as obtained in theAssay.

C: It meets the requirements for Chloride á191ñ.

Change to read:

Change to read:

Mobile phase— Prepare a filtered and degassed mixture of tert-butyl methyl ether,chromatographic n-heptane,acetonitrile,and water (63:35:2:0.2).Make adjustments if necessary (see System SuitabilityunderChromatography á621ñ).

System suitability solution— Transfer about 18mg of USP Dorzolamide Hydrochloride RSand 2mg of USP Dorzolamide Hydrochloride Related Compound A RS,each accurately weighed,to a 15-mLcentrifuge tube,dissolve in 4mLof 0.5Nammonium hydroxide,add 4mLof ethyl acetate,and mix.Separate the ethyl acetate layer,and transfer to a 15-mLcentrifuge tube.Add 4mLof ethyl acetate to the aqueous layer,mix,separate the ethyl acetate layer,and combine it with the first extract.Evaporate the combined organic layers to dryness on a water bath maintained at 50under a stream of nitrogen.Dissolve the residue in 3mLof acetonitrile,add 3drops of (S)-(-)-a-methylbenzyl isocyanate [NOTE—Discard the reagent if it is colored.],USP28and allow to react for 5minutes on a water bath maintained at 50.USP28Evaporate the mixture to dryness on a water bath maintained at 50under a stream of nitrogen.Dissolve the residue in 10mLof a mixture of tert-butyl methyl ether,glacial acetic acid,and acetonitrile (87:10:3).

Test solution— Transfer about 20mg of Dorzolamide Hydrochloride,accurately weighed,to a 15-mLcentrifuge tube,and proceed as directed for System suitability solution beginning with “dissolve in 4mL”.

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 L3.The flow rate is about 2mLper minute.Chromatograph theSystem suitability solution,and record the peak areasUSP28as directed for Procedure:the relative retention times are about 1.0for dorzolamide and 1.5for dorzolamide hydrochloride related compound A;the resolution,R,between dorzolamide and dorzolamide hydrochloride related compound Ais not less than 4.0;the column efficiency for the dorzolamide hydrochloride peakUSP28is not less than 4000USP28theoretical plates;the tailing factor is not more than 1.4;and the relative standard deviation for replicate injections determined from the dorzolamide peak is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10µL)of the System suitability solutionand theTest solutioninto the chromatograph,record the chromatograms,and measure the areas forUSP28the major peaks.Calculate the percentage of dorzolamide hydrochloride related compound Ain the portion of Dorzolamide Hydrochloride taken by the formula: in which rIis the peak area of dorzolamide hydrochloride related compound Aobtained from the Test solution;and rSis the peak area of dorzolamide hydrochloride obtained from the Test solution:not more than 0.5%is found.USP28

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Phosphate buffer,USP28Solution A,Solution B,Mobile phase,andChromatographic system— Proceed as directed in the Assay.

USP28

Test solution— Use theAssay preparation.

Procedure— Inject a volume (about 10µL)ofUSP28the Test solutioninto the chromatograph,record the chromatogram,and measure all of the peak areas.USP28Calculate the percentage of each impurity in the portion of Dorzolamide Hydrochloride taken by the formula: in which riis the peak area of each individual impurity obtained from the Test solution;and rsis the sum of all the peak areas obtained from the Test solution:not more than 0.1%of any individual impurity is found;and not more than 0.5%of total impurities is found.USP28

Change to read:

Phosphate bufferUSP28— Dissolve 3.7g of potassium phosphate in 1000mLUSP28of water.

Solution A— Prepare a filtered and degassed mixture of monobasic Phosphate bufferand acetonitrile (94:6).USP28

Solution B— Use acetonitrile.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed forChromatographic system.Make adjustments if necessary (seeSystem Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve suitable quantities of USP Dorzolamide Hydrochloride RSin Solution Ato obtain a solution having a known concentration of about 0.6mg per mL.

Assay preparation— Transfer about 60mg of Dorzolamide Hydrochloride,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Solution Ato 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.The column temperature is maintained at 35.The chromatograph is programmed as follows. Chromatograph theStandard preparation,and record the peak areasUSP28as directed for Procedure:the column efficiency is not less than 6500theoretical plates;the tailing factor is not less than 0.6and not more than 1.2;and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areasUSP28for the major peaks.Calculate the quantity,in mg,of C10H16N2O4S3·HCl in the portion of Dorzolamide Hydrochloride taken by the formula: in which Cis the concentration,in mg per mL,of USP Dorzolamide Hydrochloride RSin theStandard preparation;and rUand rSare the peak areas obtained from theAssay preparationand the Standard preparation,respectively.