Thin-layer chromatographic identification test á201ñ—
Test solution—
Transfer a portion of powdered Tablets,equivalent to about 100mg of captopril,to a conical flask.Add 25mLof methanol,stir for 30minutes using a magnetic stirrer,and centrifuge.Use the clear supernatant.
Standard solution:
4mg per mL,in methanol.
Application volume:
50µL,as streaks.
Developing solvent system:
a mixture of toluene,glacial acetic acid,and methanol (75:25:1).
Procedure—
Proceed as directed in the chapter.Locate the spots on the plate by lightly spraying with a freshly prepared mixture of 1volume of ammonium hydroxide and 6volumes of a solution of 0.04%5,5¢-dithiobis(2-nitrobenzoic acid)in methanol.
Dissolution á711ñ—
[NOTE—Completely deaerate the
Dissolution Medium to minimize exposure of captopril to air,and analyze the samples immediately.
]
Medium:
0.01Nhydrochloric acid;900mL.
Apparatus 1:
50rpm.
Time:
20minutes.
Procedure—
Determine the amount of C
9H
15NO
3Sdissolved by employing UVabsorption at the wavelength of maximum absorbance at about 205nm on filtered portions of the solution under test,suitably diluted with
Dissolution Medium,if necessary,in comparison with a Standard solution having a known concentration of
USP Captopril RSin the same
Medium.
Tolerances—
Not less than 80%(Q)of the labeled amount of C9H15NO3Sis dissolved in 20minutes.
Limit of captopril disulfide—
[NOTE—Protect solutions from exposure to air.Use within 8hours of preparation.
]
Mobile phase—
Proceed as directed in the Assay.
System suitability solution—
Dissolve suitable quantities of
USP Captopril RSand
USP Captopril Disulfide RSin
Mobile phaseto obtain a solution having known concentrations of about 1mg per mLand 0.05mg per mL,respectively.
Standard solution—
Dissolve an accurately weighed quantity of
USP Captopril Disulfide RSin
Mobile phase,and dilute quantitatively,and stepwise if necessary,with
Mobile phaseto obtain a solution having a known concentration of about 0.05mg per mL.
Test solution—
Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 25mg of captopril,to a suitable centrifuge tube.Add 25.0mLof Mobile phase,sonicate for 15minutes,and centrifuge.Use the clear supernatant as the Test solution.
Chromatographic system
(see
Chromatography á621ñ)—The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×25-cm column that contains packing L1with about 15%hydrocarbon load.The flow rate is about 1mLper minute.Chromatograph the
System suitability solutionand the
Standard solution,and record the peak responses as directed for
Procedure:the relative retention times are about 0.5for captopril and 1.0for captopril disulfide;the resolution,
R,between captopril and captopril disulfide in the
System suitability solutionis not less than 2.0;and the relative standard deviation for replicate injections of the
Standard solutionis not more than 2.0%.
Procedure—
Separately inject equal volumes (about 20µL)of the
Standard solutionand the
Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentage of captopril disulfide in the portion of Tablets taken by the formula:
2500C/W(rU/rS),
in which
Cis the concentration,in mg per mL,of
USP Captopril Disulfide RSin the
Standard solution;Wis the quantity,in mg,of captopril in the portion of Tablets taken to prepare the
Test solution,based on the labeled amount per Tablet;and
rUand
rSare the captopril disulfide peak responses obtained from the
Test solutionand the
Standard solution,respectively:not more than 3.0%is found.
Assay—
[NOTE—Protect solutions from exposure to air.Use within 8hours of preparation.
]
Mobile phase—
Prepare a filtered and degassed mixture of 550mLof methanol and 450mLof water containing 0.50mLof phosphoric acid.Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Standard preparation—
Dissolve suitable quantities of
USP Captopril RSand
USP Captopril Disulfide RSin
Mobile phaseto obtain a solution having known concentrations of about 1mg per mLand 0.05mg per mL,respectively.
Assay preparation—
Transfer not fewer than 20Tablets to a suitable volumetric flask,add Mobile phaseto fill the flask to about half of its capacity,and sonicate for 15minutes.Dilute with Mobile phaseto volume,shake by mechanical means for 15minutes,and filter.Dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a concentration of about 1mg of captopril per mL.
Chromatographic system
(see
Chromatography á621ñ)—The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×25-cm column that contains packing L1with about 15%hydrocarbon load.The flow rate is about 1mLper minute.Chromatograph the
Standard preparation,and record the peak responses as directed for
Procedure:the relative retention times are about 0.5for captopril and 1.0for captopril disulfide;the resolution,
R,between captopril and captopril disulfide is not less than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.
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 captopril (C
9H
15NO
3S)in the portion of Tablets taken by the formula:
(L/D)C(rU/rS),
in which
Lis the labeled amount,in mg,of captopril in each Tablet;
Dis the concentration,in mg per mL,of captopril in the
Assay preparationbased on the labeled quantity per Tablet and the extent of dilution;
Cis the concentration,in mg per mL,of
USP Captopril RSin the
Standard preparation;and
rUand
rSare the captopril peak responses obtained from the
Assay preparationand the
Standard preparation,respectively.