#ASSAY OF PHENOBARBITONE

Aim: To determine the percentage purity of phenobarbitone present in the given powder.

Apparatus: Burette, Pipette, Burette stand, conical flask.

Chemicals:  Silver nitrate, phenobarbitone, sodium carbonate, potassium chromate indicator.

Principle:

          Assay of phenobarbitone comes under precipitation titration. Barbiturates when interact with silver nitrate in the presence of sodium carbonate initially it forms one substituted sodium salt of phenobarbitone, which reacts with silver nitrate (AgNO₃) with the formation of soluble one-substituted Ag-salt. Then soluble Na-Ag-salt is formed. In equivalence point excess of titrant AgNO₃ destroys Na-Ag-salt and the insoluble two-substituted Ag-salt of phenobarbitone is formed, that indicates the end point.

Procedure:

Standardisation of Silver nitrate: Weigh accurately 0.5g (5ml) of NaCl and add 10ml of water in to conical flask. Add 0.5ml of indicator and titrate against AgNO₃ solution until brick red colour precipitate was formed.

                                   Each ml of 0.1M AgNO_{3 ≡} 0.005844gm of NaCl

Assay: Weigh accurately about 2.0 g of phenobarbitone, add 30 ml of water and 3 g of sodium carbonate, stirr to dissolve and titrate with 0.1 M silver nitrate until a distinct turbidity was observed when Viewed against a black background, the solution being stirred vigorously throughout the titration.

                  1 ml of 0.1 M silver nitrate is equivalent to 0.02542 g of C₁₂H₁₁N₂NaO₃.

Calculations:

Standardisation of AgNO₃:

S. No	Contents in the flask	Burette Reading		Volume Consumed	Indicator
		Initial	Final
1
2

Each ml of 0.1M AgNO₃≡ 0.005844gm of NaCl

X ml of Y M of AgNO₃≡ -----gms of NaCl

Y =

Assay:

S. No	Contents of the flask	Burette reading		Volume consumed	Indicator
		Initial	Final
1

1ml of 0.1M AgNO₃≡ 0.02542 gms of C₁₂H₁₁N₂NaO₃.

X ml of Y MAgNO₃≡ Z gm of C₁₂H₁₁N₂NaO₃.

Z=

Percentage purity = Estimated amount / Weight of powder taken

Report: The percentage purity of phenobarbitone Sodium present in given sample is found to be ………………