Aim: Determination the potency of the Penicillin G in per mg

Requirement:

  • 0.01N NaS2O3 solution
  • 0.01N I2 solution
  • 1 N NaOH solution (Approx.)
  • 1 N HCl solution (Approx.)

Process: Weigh exactly about 0.05 gm (50 mg) of the given penicillin and dissolve it in distilled water and finally make the volume 100 ml in Standard measuring flask,

Blank Estimation:

Take 5.0 ml of diluted penicillin solution, add 25 ml of the given I2 solution and titrate against 0.01N Na2S2O3 using starch as indicator. End point is marked with the disappearance of blue colour. Let the constant B.R. be A ml.

Actual Estimation:

Take 5.0 ml of penicillin solution in a iodometric flask, add 5.0 ml 1N NaOH solution. keep it for hydrolysis for half an hour. Add 6.0 ml 1N HCl solution and 25 ml of the given Iodine solution. Cork tightly and keep it for 30 min. Wash the side of flasks carefully and titrate the excess of iodine with 0.01 N Na2S2O3 solution using starch as a indicator. Let the constant B.R. be B ml.

Carry out the blank determination omitting the addition of the sulpha drug.

Potency of penicillin  = \frac{1667 \times(\mathrm{A}-\mathrm{B}) \times 20}{\mathrm{~W} \times 2.52}

                                      =                      mg

Where, A = Blank Estimation

              B  = Actual Estimation

              W = Weight of sample

Observation:

  • Blank Estimation:

Burette     : 0.01N Na2S2O3 solution

Flask         : 5.0 ml of diluted penicillin solution + 25 ml of the 0.01N I2 solution

Indicator  : Starch solution

End point : Disappearance of blue color

No. I.B.R. F.B.R. Difference Constant B.R.

A ml

01
02
  • Actual Estimation:

Burette     : 0.01N Na2S2O3 solution

Flask         : 5.0 ml of diluted penicillin solution + 5.0 ml 1N NaOH solution. ------> keep it for 30 
                    min. + 6.0 ml 1N HCl solution + 25 ml of 0.01N Iodine solution------> keep it for 30 min.

Indicator  : Starch solution

End point : Disappearance of blue color

No. I.B.R. F.B.R. Difference Constant B.R.

B ml

01
02

Calculation:

Potency of penicillin  = \frac{1667 \times(\mathrm{A}-\mathrm{B}) \times 20}{\mathrm{~W} \times 2.52}

                                      =                      mg

Where, A = Blank Estimation

              B  = Actual Estimation

              W = Weight of sample =                  mg