Question

what is the assay method of paracetamol (procedures should be discussed in details, list of chemicals/equipments should be given)???

Answer 1

INTRODUCTION

Paracetamol [acetaminophen, N-acetyl-p-aminophenol, 4-acetamidophenol] is used as analgesic and antipyretic agents .

Various spectrophotometric methods have been utilised for the determination of paracetamol, these include coupling with different diazotised reagents such as sulphanilic acid,2- nitroaniline, benzocaine and sulphacetamide.

Paracetamol can be determined by diazotization of hydrolysed paracetamol and coupling with 1-naphthol, Oxidative coupling reaction has been used in determination of paracetamol based in reaction with o-cresol , or p-xylenol after hydrolysis to p-aminophenol with an oxidizing agent such as sodium periodate.

Paracetamol can be determined by nitration and subsequent reaction with acetone as nucleophilic reagent or by complexation with Co(III) and Cu(II) ions. Another method based on reaction of hydrolysed paracetamol (p-aminophenol) at ambient temperature with sodium sulphide in the presence of Ce(IV) or Fe (III) to produce a methylene blue-like dye . Also, a charge transfer complex formation has been used for the determination using 2,3-dichloro- 5,6-dicyano-1,4- benzoquinone. Oxidation reduction reaction can be used in the determination of paracetamol using Fe (III) in the presence of 2,2`-bipyridyl.

Many chromatographic methods have been published. These included high performance liquid chromatography, gas chromatography and liquid chromatography.

The present method involves the diazotisation of hydrolysed paracetamol, followed by coupling with phloroacetophenone to form a highly coloured dye that has been applied successfully to the assay of paracetamol in pharmaceutical preparations.

Experimental Instruments:-

All spectrophotometric measurements are performed on Shimadzu UV-Visible Recording Spectrophotometer UV-160 using 1- cm silica cells, pH meter type Philips PW 9420 is used for pH reading.

Reagents:-

All chemicals used in this investigation are of analytical – reagent grade, and paracetamol standard material is provided from general establishment for medical appliance and drugs.

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Nabeel Sabeh Othman & Safaa Abdul Aleem Zakaria

Reagents

All chemicals used in this investigation are of analytical – reagent grade,

and paracetamol standard material is provided from general establishment

for medical appliance and drugs / SDI – Samaraa / Iraq.

Solutions

Paracetamol solution , 1000 microg.ml-1. :- This solution is prepared by dissolving 0.25 gof paracetamol in 10 ml of ethanol and diluted to 250 ml in a volumetric flask with distilled water.

Phloroacetophenone , 0.1% (w/v). :-This solution is prepared fresh daily by dissolving 0.1 g of phloroacetophenone (Fluka) in 100 ml distilled water.

Sodium nitrite solution, 1% (w/v). :- This solution is prepared by dissolving 1 g of sodium nitrite (BDH) in 100 ml distilled water.

Sulphamic acid solution, 3% (w/v). :- This solution is prepared by dissolving 3 g of sulphamic acid (Fluka) in 100 ml distilled water.

Hydrochloric acid solution, 1N. This solution is prepared by diluting 8.5 ml of concentrated acid (11.8 N) to 100 ml with distilled water.

Solution of hydrolyzed paracetamol, , 100 Microg.ml-1.:- This solution is prepared by transferring 150 ml of 1000microgram.ml-1paracetamol into 250- ml round-bottomed flask provided with condenser,25ml of hydrochloric acid(11.8N) is added then refluxed for 1 hour, after that the cold solution is neutralised with 20% sodium carbonate and diluted to 250 - ml with distilled water in a volumetric flask. To prepare 100g.ml-1 paracetamol, 16.6 ml of the above solution is diluted to 100 ml in a volumetric flask using distilled water.

Paracetamol tablets solution, 100g.ml-1. :- 10 tablets (each one contains 500 mg paracetamol) are weighed and finely powdered. An accurately weighed amount of powder equivalent to 0.25g paracetamol is dissolved in 10 ml ethanol, then 100-150 ml distilled water is added, shaking to increase the solubility, filtered into 250 ml calibrated flask, then the solution is completed to the volume with a distilled water, and proceed as mentioned above in preparation of hydrolysed paracetamol solution.

Paracetamol syrup solution, microgram.ml-1. :-A 10.4 ml of syrup (each 5ml contains 120 mg paracetamol) is transferred into a 250 ml calibrated flask and the total volume is diluted with distilled water, and proceed as mentioned in preparation of hydrolysed paracetamol solution.

Procedure:-

To a series of 25 - ml calibrated flasks, transfer 0.1 – 2.2 ml of hydrolysed paracetamol solution (equivalent to 100 g.ml-1 paracetamol) , then 0.5 ml of 1N hydrochloric acid and 0.5 ml of 1% (w/v) sodium nitrite solution are added and the mixture is allowed to stand for 5 minutes and then 0.2 ml of 3% (w/v) sulphamic acid solution is added with occasional shaking for 2 minutes. After that a 2 ml of 0.1% (w/v) phloroacetophenone solution and 2 ml of 1N sodium hydroxide are added . The volumes are completed to the mark with distilled water and the absorbance is read at 472 nm against the reagent blank after 10- minutes standing time. A linear calibration graph is obtained over the concentration range of 10 – 180 g paracetamol / 25 ml and a concentration above 180 g / 25 ml gives a negative deviation.The molar absorptivity has been found to be 2.16104 l.mol-1.cm-1.