Identification
A:
Infrared Absorption 197M.
B:
The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.
Change to read:
Limit of dorzolamide hydrochloride related compound A
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 Suitability under
Chromatography 621).
System suitability solution
Transfer about 18 mg of
USP Dorzolamide Hydrochloride RS and 2 mg of
USP Dorzolamide Hydrochloride Related Compound A RS, each accurately weighed, to a 15-mL centrifuge tube, dissolve in 4 mL of 0.5 N ammonium hydroxide, add 4 mL of ethyl acetate, and mix. Separate the ethyl acetate layer, and transfer to a 15-mL centrifuge tube. Add 4 mL of 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 50
under a stream of nitrogen. Dissolve the residue in 3 mL of acetonitrile, add 3 drops of
(S)-(
)-
-methylbenzyl isocyanate
[NOTEDiscard the reagent if it is colored.
], and allow to react for 5 minutes on a water bath maintained at 50
. Evaporate the mixture to dryness on a water bath maintained at 50
under a stream of nitrogen. Dissolve the residue in 10 mL of a mixture of
tert-butyl methyl ether, glacial acetic acid, and acetonitrile (87:10:3).
Test solution
Transfer about 20 mg of Dorzolamide Hydrochloride, accurately weighed, to a 15-mL centrifuge tube, and proceed as directed for System suitability solution beginning with dissolve in 4 mL.
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 L3. The flow rate is about 2 mL per minute. Chromatograph the
System suitability solution, and record the peak areas as directed for
Procedure: the relative retention times are about 1.0 for dorzolamide and 1.5 for dorzolamide hydrochloride related compound A; the resolution,
R, between dorzolamide and dorzolamide hydrochloride related compound A is not less than 4.0; the column efficiency for the dorzolamide hydrochloride peak is not less than 4000 theoretical plates; the tailing factor is not more than 1.4.
USP29
Procedure
Separately inject equal volumes (about 10 µL) of the
System suitability solution and the
Test solution into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the percentage of dorzolamide hydrochloride related compound A in the portion of Dorzolamide Hydrochloride taken by the formula:
100rI / (rI + rS)
in which
rI is the peak area of dorzolamide hydrochloride related compound A obtained from the
Test solution; and
rS is the peak area of dorzolamide hydrochloride obtained from the
Test solution: not more than 0.5% is found.
Chromatographic purity
Phosphate buffer, Solution A, Solution B, Mobile phase, and Chromatographic system
Proceed as directed in the Assay.
Test solution
Use the Assay preparation.
Procedure
Inject a volume (about 10 µL) of the
Test solution into the chromatograph, record the chromatogram, and measure all of the peak areas. Calculate the percentage of each impurity in the portion of Dorzolamide Hydrochloride taken by the formula:
100(ri / rs)
in which
ri is the peak area of each individual impurity obtained from the
Test solution; and
rs is 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.
Change to read:
Assay
Phosphate buffer
Dissolve 3.7 g of
monobasic
USP29 potassium phosphate in 1000 mL of water.
Solution A
Prepare a filtered and degassed mixture of
Phosphate buffer and acetonitrile (94:6.5).
USP29
Solution B
Use acetonitrile.
Mobile phase
Use variable mixtures of
Solution A and
Solution B as directed for
Chromatographic system. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation
Dissolve suitable quantities of
USP Dorzolamide Hydrochloride RS in
Solution A to obtain a solution having a known concentration of about 0.6 mg per mL.
Assay preparation
Transfer about 60 mg of Dorzolamide Hydrochloride, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Solution A 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. The column temperature is maintained at 35
. The chromatograph is programmed as follows.
Time (minutes) |
Solution A
(%) |
Solution B
(%) |
Elution |
015 |
100 |
0 |
isocratic |
1530 |
100®50 |
0®50 |
linear gradient |
3037 |
50®100 |
50®0 |
linear gradient |
3744 |
100 |
0 |
isocratic |
Chromatograph the
Standard preparation, and record the peak areas as directed for
Procedure: the column efficiency is not less than 6500 theoretical plates; the tailing factor is not less than 0.6 and 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 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of C
10H
16N
2O
4S
3·HCl in the portion of Dorzolamide Hydrochloride taken by the formula:
100C(rU / rS)
in which
C is the concentration, in mg per mL, of
USP Dorzolamide Hydrochloride RS in the
Standard preparation; and
rU and
rS are the peak areas obtained from the
Assay preparation and the
Standard preparation, respectively.