Aim: Assay of a given sample of Benzylpenicillin by Iodine titration.
BACKGROUND
Here, Benzylpenicillin is assayed by the direct iodometric titration method. In this titration, an excess iodine is taken such that iodine remain in the solution even after the completion of the reaction with penicilloic acid, which is formed due to reaction of NaOH with benzylpenicillin and such remaining iodine is titrated against standard sodium thiosulphate solution. The colour change at endpoint is blue to apple green or yellow.
Reactions:
Factor Calculation:
4 Mol Iodine ≡ 8 Mol Sodium thiosulphate ≡ 1 Mol Benzylpenicillin
≡1Mol Sodium Benzylpenicillin
Each ml of 0.01N Sodiumthiosulphate ≡ 334.4/800000 = 0.000418 g Benzylpenicillin
≡ 356.4/800000 = 0.0004455 g Sodium Benzylpenicillin
REQUIREMENTS
Chemical required:
Benzylpenicillin, 1 N NaOH, 1 N HCl, 0.01N Iodine, 0.01N Na2S2O3, Freshly prepared Starch Solution.
PROCEDURE
For Standardisation of sodium thiosulphate
For Assay- Prepare a standard solution by taking weight equivalent to 0.1 to 0.12 g of Benzylpenicillin in DW and dilute to 100 ml in a volumetric flask. Transfer 5.0 ml to an iodine flask, add 5 ml of 1N sodium hydroxide and allow to stand for 30 minutes. Now, add, 6 ml of 1N HCl and 25.0 ml of 0.01N iodine solution. Close the flask with a wet glass-stopper and allow to stand for 30 minutes in a dark place (i.e., protected from light). Titrate the excess of iodine with previously standardised 0.01 N sodium thiosulphate, employing freshly prepared starch solution as an indicator added towards the endpoint till the discharge of the blue color. Note the volume of titrant as A. Repeat the titration for concordant reading.
For Blank- To a flask containing 5.0 ml of the Standard Preparation add 25.0 ml of 0.01 N iodine. Titrate the iodine with 0.01 N previously standardised sodium thiosulphate, taking starch solution as indicator. Take the volume of titrant as B. Repeat the titration for concordant reading.
Observation Table:
For Assay:
Sr No. | Initial Burette Reading (IBR in ml) | Final Burette Reading (FBR in ml) | Difference (in ml) | Mean (A in ml) |
---|---|---|---|---|
01 |
|
|
|
|
02 |
|
|
|
|
03 |
|
|
|
|
For Blank:
Sr No. | Initial Burette Reading (IBR in ml) | Final Burette Reading (FBR in ml) | Difference (in ml) | Mean (B in ml) |
---|---|---|---|---|
01 |
|
|
|
|
02 |
|
|
|
|
03 |
|
|
|
|
Calculation:
Volume of sodium thiosulphate equivalent to benzylpenicillin is (B-A) ml
For 5 ml standard solution, equivalent amount of sodium thiosulphate = (B-A) ml
For 100 ml standard solution, ————————————————–= 20 (B-A) ml = V
CONCLUSION
The Assay value of the sample is _________________________________%
REFERENCES
- United States Pharmacopeia (2023). General Chapter, 〈425〉 Iodometric Assay—Antibiotics. USP-NF. Rockville, MD: United States Pharmacopeia. DOI: https://doi.org/10.31003/USPNF_M99185_02_01
- Kar A. Pharmaceutical drug analysis. New Age International; 2005. P- 143.
- Garratt DC. The quantitative analysis of drugs. Springer Science & Business Media; 2012, p- 51.
FAQs
Benzylpenicillin, also known as penicillin G, inhibits the third and last stage of bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs) and then
Benzylpenicillin is a beta-lactam antibiotic.
Pharmacopeial penicillin antibiotic drugs and their dosage forms are assayed by iodimetry.
Also read:
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- Purification of Immunoglobulin by Precipitation
- Microplate based Alamar Blue Assays
- Isolation of Genomic DNA from E. coli
- Estimation of DNA and its purity check using UV spectrophotometer (A260 measurement)
- Isolation of O & H Antigen from Salmonella typhi
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