Identification of diazepam Potentiometric Titration( Non-aqueous titration)

 Molecular Formula: C16H13CLN2O Molecular Mass: 284.7

 

 

Chemical Name: 7-Chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one

General Requirement: Diazepam contains not less than 99.0% and not more than 101.0% of C16H13CLN2O , calculated with reference to the dried substance

Assay

Dissolve about 0.55 g , accurately weighed, in 30 ml of glacial acetic acid ,and titrate with perchloric acid (0.1M) VS, determining the end point by using potentiometrically

  Potentiometric Titration( Non-aqueous titration)

Reagents

     standard(0.1M)HCLO4 solution

    Glacial acetic acid

Diazepam Tablet

Apparatus

    , Beaker,    Magnetic stirrer and stirring bar, pH-meter

procedures

Accurately weight 250 mg or 0.55gm of sample( tablet ) and transfer to a 250 ml beaker

Add 30 ml of glacial acetic acid. and wait a few minutes .The tablet should crumble. To the tablet in the beaker now stir the tablet with a glass rod  until it dissolves

Note: the white solid that dissolves slowly is starch and it may not dissolve completely

Place the beaker containing the sample on a magnetic stirrer

Titrate this solution using the procedure of the following

A.  Wash the pH electrode off distilled water and dry carefully using a kimiwipe

B.  Carefully immerse the electrodes of previously standardized pH-meter into the Diazepam solution

C.  Fill the burette with standard (0.1N) HCLO4

 Note:  before starting the magnetic stirrer be absolutely certain that the magnetic stirring bar will not strike the electrode

D.    Determine the pH of the solution before adding any 0.1N HCLO4 titrant, and record this value

E.  Add 3ml of (0.1N) HCLO4 of the beaker from burette. Stir the solution carefully and note the potential after 15 seconds, and record both milliliters of titrant and pH of the solution

F.   Continue the procedure for every addition of 3ml of (0.1N) HCLO4 till the potential of the solution shows a tendency to increase rapidly, at this stage, add (0.1N) HCLO4 in increments of 0.3ml and note the PH after each addition, also note the increments which give the greatest difference in pH . This pH contains the equivalence point. When the PH increase is small, stop noting the PH

G.Put the result in the table

H.  Prepare a graph by plotting pH values against volume of (0.1N)HCLO4.  The  end point of the titration may be determined graphically by drawing a vertical line from the midpoint of the steepest part of the titration curve to the X axis

The point where this line intersects the X axis is then taken as the volume of titrant consumed at the equivalence point.(…….A...ml)

I.Calculate the % Diazepam Tablet