Colourimetric Assay for Paracetamol - Essay Example

ble results. The chief advantage of colourimetric methods is that they provide a simple means for determining minute quantities of substances. The upper limit of colorimetric methods is in general the determination of constituents which are present in quantities of less than 1 or 2 per cent (J. W. Robinson). The principle behind any colourimetric technique for paracetamol analysis is that paracetamol undergoes oxidation-reduction reaction with an aqueous solution of iron(III) ion. In the reaction, iron(III) ions are being reduced to iron(II) ions.

The iron(II) ions produced in the redox reaction is reacted with potassium hexacyanoferrate(III) solution forming prussian blue which is an intense blue colored complex. The concentration of the paracetamol in a given solution may be determined by measuring the color intensity of the Prussian blue solution. . Upon measurement of the intensity in terms of absorbance, Beer’s law is used to calculate the concentration of the paracetamol in micrograms per milliliter. To permit selection of the most advantageous technique, effects of variables such as temperature, heating time, acidity and reagent concentration have been evaluated.

Another simple, accurate and fast method of determination of paracetamol is based on the measurement of the intensity of the yellow color that will develop when the sample containing paracetamol is reacted with p-dimethylaminobenzaldehyde in 2 molar solution of hydrochloric acid after heating (Usifoh, et. al.). This yellow color is usually absorbed in the visible region where the wavelength is 450 nm. It is normally stable for several hours and its intensity is directly proportional to the concentration of the drug, that is, Beer’s law is obeyed.

This colorimetric technique is mainly used for analysis where the paracetamol is contained in a particular raw material or in pharmaceutical dosage forms such as tablets and syrups. Finally, a fast, automated colorimetric method for the determination of samples containing paracetamol is the latter’s reaction with acidic hypochlorite followed by coupling with alkaline phenol which produces a blue indophenol dye, which is measured colourimetrically (J.W. Murfin). This method is generally used for tablets containing paracetamol and a granule formation containing paracetamol.

MATERIALS AND METHOD A stock solution of paracetamol has been prepared for analysis. The stock solution is prepared by dissolving appropriate amount of 0.0023 mol/L paracetamol solution in 10 mL of NaCl solution and made