A: Powder 5Tablets,mix with 20mLof water,and filter:the filtrate responds to the tests for Potassium á191ñ.

B: Aportion of powdered Tablets containing about 50mg of potassium citrate responds to the test for Citrate á191ñ,20mLof the mixture of pyridine and acetic anhydride being used.

Medium: water;900mL.

Apparatus 2: 50rpm.

Times: 30minutes,1hour,and 3hours.

Potassium stock solution and Standard preparation—Prepare as directed in the Assayunder Potassium Chloride Oral Solution.

Procedure— Filter the solution under test,and dilute quantitatively with Dissolution Mediumto obtain a test solution containing about 60µg of potassium citrate per mL.Transfer 5.0mLof the test solution to a 100-mLvolumetric flask,add 2.0mLof sodium chloride solution (1in 5)and 1.0mLof hydrochloric acid,dilute with water to volume,mix,and proceed as directed for Procedurein the Assayunder Potassium Chloride Oral Solution.Calculate the quantity,in mg,of C6H5K3O7dissolved by the formula: in which Fis the extent of dilution of the solution under test,2.612is the ratio of the molecular weight of anhydrous potassium citrate to three times the atomic weight of potassium,and Cis the concentration,in µg per mL,of potassium in the test solution.

Tolerances— The percentages of the labeled amount of C6H5K3O7dissolved from the Tablets are not more than 45%(Q)in 30minutes,not more than 60%(Q¢)in 1hour,and not less than 80%(Q¢¢)in 3hours.The requirements are met if the quantities dissolved from the Tablets tested conform to the accompanying table instead of the table shown under Dissolution á711ñ.

Stage	Number Tested	Acceptance Criteria
S1	6	Each unit is within the range between Q±10%and Q¢±10%,and is not less than Q¢¢+5%at the stated Times.
S2	6	Average of 12units (S1+S2)is within the range between Q±10%and Q¢±10%and is not less than Q¢¢;no unit is outside the range between Q±15%and Q¢±15%,and no unit is less than Q¢¢-5%at the stated Times.
S3	12	Average of 24units (S1+S2+S3)is within the range between Q±10%and Q¢±10%and is not less than Q¢¢;not more than 1unit is outside the range between Q±15%,not more than 1unit is outside the range between Q¢±15%,and not more than 1unit is less than Q¢¢-5%at the stated Times.

Potassium stock solutionand Standard preparations— Prepare as directed in the Assayunder Potassium Chloride Oral Solution.

Assay preparation— Transfer 3.0mLof the clear filtrate,reserved from the Assay,to a 100-mLvolumetric flask,add 2.0mLof sodium chloride solution (1in 5)and 1.0mLof hydrochloric acid,dilute with water to volume,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Potassium Chloride Oral Solution.Calculate the quantity,in mg,of potassium (K)in the portion of Tablets taken by the formula: in which Cis as defined therein:the quantity,in mg,of potassium found in the portion of Tablets taken is not less than 36.4%and not more than 40.2%of the quantity,in mg,of potassium citrate in the portion of Tablets taken,as determined in the Assay.

Standard preparation— Dissolve a suitable quantity of citric acid,previously dried at 90for 3hours and accurately weighed,in water to obtain a solution having a known concentration of about 1.0mg of anhydrous citric acid 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 potassium citrate,to a 1000-mLvolumetric flask,add about 300mLof hot water,and shake by mechanical means for 15minutes.Allow to cool,dilute with water to volume,and mix.Filter,discarding the first 30mLof the filtrate.Transfer 20.0mLof the clear filtrate to a 25-mLvolumetric flask,dilute with water to volume,and mix.[NOTE—Reserve the remaining filtrate for the test for Potassium content.]

Standard curve— Pipet aliquots of 8,9,10,11,and 12mL,respectively,of the Standard preparationinto separate 100-mLvolumetric flasks,dilute with water to volume,and mix.These solutions contain about 0.08,0.09,0.10,0.11,and 0.12mg of anhydrous citric acid per mL,respectively.Continue as directed for Procedure.Plot the resultant absorbances versus the respective concentrations,in mg per mL,of the standard solutions.

Procedure— Pipet 1mLof the Assay preparationinto a suitable test tube.To a second test tube add 1.0mLof water to serve as a reference blank.To each tube add 1.3mLof pyridine,and mix by swirling.To one tube at a time add 5.7mLof acetic anhydride,and mix,using a rotary vortex stirrer.Immediately place in a water bath maintained at 31±1.0,and allow the color to develop for 33±1minutes.Determine the absorbance against the reference blank in 2.5-cm cells at 425nm,taking care to measure the absorbance of each solution at the same elapsed time from mixing.Calculate the quantity,in mg,of C6H5K3O7in the portion of Tablets taken by the formula: in which 306.40and 192.13are the molecular weights of anhydrous potassium citrate and anhydrous citric acid,respectively,and Cis the concentration,in mg per mL,of anhydrous citric acid read from the Standard curve.