COLOURIMETRY PARACETAMOL - Essay Example

? COLOURIMETRIC ASSAY FOR PARACETAMOL Chemistry 21 February Colourimetric Assay for Paracetamol Introduction Colourimetry is a chemical technique that quantifies the absorption of visible light by coloured solutions (Vijayasarathi 2008). The quantity of the absorbed light depends on the strength of the solution. When monochromatic light goes through a coloured solution in a cell, a portion of the radiation is taken in and another fraction is transmitted. Colourimetry is a hands-on application of the Beer-Lambert law to establish the proportion of light that is transmitted by a solution containing a coloured solute, and using that information to ascertain the concentration of the solute (Thompson 2008). Plotting the values of absorbance against concentration produces a straight line that passes through the origin. Colourimetry is an extremely useful technique in establishing the concentration of substances. This is achieved by preparing a known concentration series of about 4 solutions, after which their absorbance is determined after the addition of colour by a reagent. The absorbance values give a calibration curve from which the concentration of an unknown substance is established. This technique is useful in the determination of metal ions alloys and biological fluids (Vijayasarathi 2008). Numerous industrial and clinical experiments report the successful usage of colorimetric procedures in the establishment of the concentrations of chemical substances. For example, the determination of vitamin E in food (Christie, Dean & Millburn 1973), trace amounts of platinum in glass (Fuller, Himsworth & Whitehead 1971), flavonoids in food, and detection of alpha fetoproteins (Xiang et al. 2012) among many other uses. Paracetamol (4-acetamedophenol) is a commonly used painkiller that lessens the temperature of fever patients (Osborne 2002). Its pain reducing effects are known as analgesic effects whereas its fever reduction action is called the antipyretic effect (Bose et al. 2005). Numerous over the counter medications contain paracetamol especially those meant for the relief of colds and flu. The most common form is the 500 mg tablet though other formulations such as suspensions and suppositories also exist (Acetaminophen n.d.). Paracetamol is quickly taken in from the gastrointestinal tract and attains peak plasma concentrations in about an hour (Acetaminophen n.d.). The cytochrome P450 system metabolises it into N-acetyl-p-benzoquinamine (NAPQI), a toxin that is entirely detoxified through conjugation with glutathione and excreted. Paracetamol is a fairly safe drug. However, doses greater than 10 grams have been reported to cause toxicity (Bose et al. 2005). This experiment aimed at using colourimetry as a chemical technique to make a calibration curve of absorbance against concentration for known paracetamol concentrations and using it to obtain the concentration of paracetamol in the sample with the unknown concentration. Materials and Method 100 ml of 0.002M paracetamol solution was prepared by dissolving the right quantity of the drug in 10 ml of sodium chloride solution and topping up to 100 ml. This was the stock solution for the experiment. 1.0 ml of 6M HCl and 2 ml of 10% sodium nitrite were added to each of the seven labelled test tubes. Paracetamol and water were then added to the tubes in predetermined quantities after which the tubes were methodically mixed and allowed to rest for about 2 minutes. 2 ml of 15% sodium sulphamate were carefully added to the test tubes followed by 2.5 ml of 25% sodium hydroxide. The tubes were shaken for 15 seconds and allowed to stand for 2 minutes. This allowed all the bubbles to disperse. The absorbance of the contents of tubes 2 to 7 was then read at a wavelength of 430 nanometers using tube 1 as the blank. The values of absorbance were recorded for each concentration of paracetamol. A calibration graph of absorbance against concentration (mol/L) was then plotted and used to approximate the concentration of the unknown test solution by extrapolation. Results Table 1: Concentration of paracetamol and observed absorbance Tube 1 2 3 4 5 6 7 Concentration of paracetamol in mol/L 0 4.0? 10-4 8.0? 10-4 1.2? 10-3 1.6? 10-3 2.0? 10-3 0 Absorbance 0 0.025 0.450 0.567 0.525 0.721 0.156 The concentrations of paracetamol in the test tubes (in mol/L) were obtained by multiplying the volume of the stock solution by the concentration of the stock solution, which was 0.002 mol/L. It was observed that the absorbance values increased as the concentration of paracetamol increased. Figure 1: The calibration graph of absorbance against concentration The absorbance values were plotted against the concentration of paracetamol in mol/L. A straight line passing through the origin was obtained by looking for the best line of fit (a line that utilizes a majority of the points while maintaining a balance on both sides of the line). The concentration of paracetamol in the unknown sample was obtained by extrapolating the recorded absorbance value on the calibration graph and reading the concentration value that coincided with the absorbance on the x-axis. It was observed that the amount of paracetamol in the unknown sample was 4.2 ? 10-4 mol/L. Discussion It is important to measure paracetamol concentration in biological fluids because it helps to predict and avoid incidences of toxicity in otherwise asymptomatic patients (Dawson & Whyte 1999). According to Yaman, Isbilir, Cakir, and Uysal, the liver metabolises paracetamol into a toxic derivative called N-acetyl-p-benzoquinamine (NAPQI) that accumulates as the concentration of paracetamol increases and causes mitochondrial dysfunction hence hepatic necrosis (2011). In addition, it is vital to check serum concentrations of paracetamol in incidences of suspected overdose, toxicity, or abuse (Bose et al. 2005). Supposed patient’s non-compliance and inspecting for acetaminophen as a co-ingestant are also factors that may necessitate the establishment of paracetamol concentrations in body fluids (Bose et al. 2005). Sometimes it is also necessary to check serum concentrations of paracetamol to monitor liver and kidney function in patients to ensure that the drug is properly metabolized to avert toxicity. Conclusion It was concluded that colourimetry was an extremely useful technique for the establishment of unknown concentrations of substances. It was realized that its accuracy relied on the accuracy of the entire process during the preparation of the calibration curve. References Acetaminophen n.d., viewed 21 February 2013, . Bose, D., Durgbanshi, A., Martinavarro-Dominguez, A., Capella-Peiro, M. E. Carda-Broch, S., Esteve-Romero J. S. & Gil-Agusti, M. T 2005, ‘Rapid determination of acetaminophen in physiological fluids by liquid chromatography using SDS mobile phase and ED detection,’ Journal of Chromatographic Science, vol. 43 no. 2005, pp 313-318. Christie, A. A., dean, C. A, & Millburn, B. A 1973, ‘The determination of vitamin E in food by colorimetry and gas-liquid chromatography,’ Analyst, vol. 1973 no. 98, pp 161-167. Dawson, A. H. & Whyte I. M 1999, ‘Therapeutic drug monitoring in drug overdose,’ British Journal of Clinical Pharmacology, vol. 48 no.3, pp 278–283. Fuller, C. W., Himsworth, G & Whitehead, J 1971, ‘Determination of trace amounts of platinum in glass by colorimetry, spark-source mass spectrography and x-ray fluorescence spectrometry,’ Analyst, vol. 1971 no. 96, pp 177-185. Osborne, C 2002, Paracetamol: a curriculum resource, Royal Society of chemistry, London. Thompson, R 2008, Illustrated guide to home chemistry experiments: all lab, no lecture, O’Reilly Media Inc., Sebastopol, CA. Vijayasarathi, R. P 2008, Engineering chemistry, Prentice Hall of India, New Delhi. Yaman, H., Isbilir, S., Cakir, E., & Uysal, B 2011, ‘Current issues with paracetamol induced toxicity,’ Journal of Experimental and Integrative Medicine, vol.1 no. 3, pp 165-166. Xiang, X., Chen, L., Zhang, C., Luo, M., Ji, X., & He, Z 2012, ‘A fluorescence-based colorimetric droplet platform for biosensor application to the detection of ?-fetoprotein,’ Analyst, vol. 2012 no.137, pp 5586-5591. Read More