Solution— Powder a number of Tablets,equivalent to about 50mg of methyclothiazide,and transfer to a 100-mLvolumetric flask with the aid of methanol.Add about 60mLof methanol,and shake the flask for 1hour.Dilute with methanol to volume,mix,and centrifuge a portion of the solution.Pipet 2mLof the clear supernatant into a second 100-mLvolumetric flask,dilute with methanol to volume,and mix:the UVabsorption spectrum of this solution exhibits maxima and minima only at the same wavelengths as that of a similar solution of USP Methyclothiazide RS.

Medium: 0.01Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

Procedure— Determine the amount of C9H11Cl2N3O4S2dissolved by employing UVabsorption at the wavelength of maximum absorbance at about 270nm 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 Methyclothiazide RSin the same Medium.An amount of alcohol not to exceed 1%of the total volume of the Standard solution may be used to dissolve USP Methyclothiazide RSprior to dilution with Dissolution Medium.

Tolerances— Not less than 70%(Q)of the labeled amount of C9H11Cl2N3O4S2is dissolved in 60minutes.

Procedure for content uniformity— Transfer 1finely powdered Tablet to a 50-mLvolumetric flask,add about 30mLof methanol,and shake by mechanical means for 1hour.Dilute with methanol to volume,mix,and centrifuge a portion of the mixture.Dilute quantitatively with methanol to obtain a solution containing approximately 10µg per mLof methyclothiazide.Concomitantly determine the absorbances of this solution and a Standard solution of USP Methyclothiazide RSin the same medium,having a known concentration of about 10µg per mL,in 1-cm cells at the wavelength of maximum absorbance at about 267nm,with a suitable spectrophotometer,using methanol as the blank.Calculate the quantity,in mg,of C9H11Cl2N3O4S2in the Tablet taken by the formula: in which Tis the labeled quantity,in mg,of methyclothiazide in the Tablet;Cis the concentration,in µg per mL,of USP Methyclothiazide RSin the Standard solution;Dis the concentration,in µg per mL,of methyclothiazide in the solution from the Tablet,based upon the labeled quantity per Tablet and the extent of dilution;and AUand ASare the absorbances of the solution from the Tablet and the Standard solution,respectively.

Standard preparation— Transfer about 20mg of USP Methyclothiazide RS,accurately weighed,to a 100-mLvolumetric flask,add methanol to volume,and mix.Transfer 10.0mLof this solution to a 200-mLvolumetric flask,add chloroform to volume,and mix.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 2mg of methyclothiazide,to a 150-mLbeaker,add 2.0mLof methanol,mix,allow the mixture to stand for 30minutes while taking precautions against loss of solvent,add 2.0mLof 0.1Msodium bicarbonate,and mix.

Procedure— [NOTE—Use water-saturated solvents throughout this procedure.]Mix about 3g of chromatographic siliceous earth with 2.0mLof 0.1Msodium bicarbonate in a 150-mLbeaker.Pack the mixture into a 25-×200-mm chromatographic column.Add 4g of chromatographic siliceous earth to the Assay preparation,mix,transfer the mixture to the column,and pack.Dry-wash the beaker with 1g of the siliceous earth mixed with 3drops of water,and transfer to the column.Place a small pad of glass wool above the column packing,pass 75mLof a mixture of isooctane and ether (9:1)through the column,and discard the eluate.Using a 200-mLvolumetric flask as a receiver,pass 100mLof chloroform through the column,wash the tip of column with ether,add 10.0mLof methanol,dilute with chloroform to volume,and mix.Concomitantly determine the absorbances of this solution and the Standard preparationat the wavelength of maximum absorbance at about 268nm,with a suitable spectrophotometer,using chloroform as the blank.Calculate the quantity,in mg,of methyclothiazide (C9H11Cl2N3O4S2)in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Methyclothiazide RSin the Standard preparation;and AUand ASare the absorbances of the solution from the Assay preparationand the Standard preparation,respectively.