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Method's of Drug Characterisation

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Introduction

Experiment 6 - Methods of Drug Characterization Aims 1. To gain experience of the analytical methods used for drug characterization Objectives 1. To gain experience in melting point determination, thin layer chromatography and UV spectroscopy 2. Application of the methods to identify an unknown substance Introduction The 2 most basic analytical techniques for identification of organic compounds are melting point determination and thin layer chromatography. Identification of compounds relied upon melting point determination before the modern analytical techniques of nuclear magnetic resonance, infrared and UV spectroscopy. Although thin layer chromatography still plays an important role in organic analysis. A solution of the unknown is spotted onto the silica coated plate about 1cm from the bottom and dried; it is then placed vertically into a tank with a suitable solvent inside. The solvent moves up the plate by capillary action and resolves the sample into discrete spots. The plate is removed and dried and the spots are viewed under UV or by treating it chemically with developing agent. For each component of the sample an Rf value can be calculated: Rf = distance moved by solute/distance moved by solvent Safety * ...read more.

Middle

Results Calculation of Rf for Unknown B Calculation of Rf for Unknown G Rf =3.9/9.2 Rf =3.2/9.2 Rf= 0.42 Rf= 0.35 Fig 1: A table showing the melting points and Rf values for the unknown compounds B and G Compound Melting point (�C) Rf (10% EtOH/Hexane) Unknown B 65-67 0.42 Unknown G 125-127 0.35 Fig 2: Absorbance against wavelength graph for Metroclopromide diluted in acetonitrile Wavelength for maximum absorption = 302nm Absorption value = 1.86 50% acetonitrile and 50% metroclopromide Discussion Identification The melting point of unknown B is 65-67�C and therefore falls into group 1. Once the Rf value was calculated at 0.42 it is possible to identify it as the compound chloro-m-cresol. The melting point of unknown G is 125-127�C and therefore falls into group 4. Once the Rf value was calculated at 0.35 it is possible to identify it as the compound methyl-4-hydroxybenzoate. The unknown compounds were determined mainly from the melting point because this is a more accurate method, whereas the Rf value can deviate largely from the correct value. ...read more.

Conclusion

The different compounds will travel at different rates depending on their solubility in the solvent. If a polar solvent is used then the polar parts of the sample will travel up the plate faster than the non polar parts of the sample.[2] The compounds will also differ in the strength of their adsorption to the adsorbent on the plate. This produces an ascending chromatographic separation. UV spectroscopy is used to determine the wavelength at which absorbance is a maximum, this wavelength is characteristic to each compound and provides information on the electronic structure of the compound.[3] Conclusion Unknown compound B is chloro-m-cresol and unknown compound G is methyl-4-hydroxybenzoate. Chloro-m-cresol is used as a preservative for adhesives, glues, polymer dispersions and emulsions whilst methyl-4-hydroxybenzoate is used for preservatives in food, cosmetics, sunscreens and shampoos. These analytical methods used are very important in drug characterization to help identify unknown compounds. Thin layer chromatography and melting point determination are both cheap, simple and quick to carry out and therefore are the most useful to use, although the most accurate method is melting point determination if carried out appropriately[4]. Other identification methods that can be used are nuclear magnetic resonance and UV spectroscopy. ...read more.

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5 stars. Overall, this is a good report. It is clearly presented, concise and well structured. There are some small issues of language and poor referencing but does not substantially retract from the reports quality. The student has shown good understanding of the major concepts behind the lab work.

Marked by teacher Alex Price 31/03/2012

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