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EXPERIMENT 3 TLC ANALYSIS OF ANALGESIC DRUGS Hazard %Yarning: Most of the organic compounds used in this experiment are hazardous compounds; and should he used in the fume hood, Wear appropriate gloves, protective eyeglasses or chemical safety goggles, and protective clothing. Dangerous goods & hazardous substances in this experiment are: ethanol TLC solvent (Iflamble), Ethyl acetate (Flammable, Irritant), Iodine (Corrosive, Harmful, And Environmental Hazard)
INTRODUCTION Frequently a chemist may be called upon to identify a particular unknown substance, If there is no prior information to work from, this can be a formidable task. There are several million known compounds, both inorganic and organic. For a completely unknown substance, the chemist must often draw on every method available. If the unknown substance is a mixture, then the mixture must be separated into its components and each component identified separately. A pure compound can often be identified from its physical properties, (nip, bp, density, refractive index, etc) and a knowledge of its functional groups. These may be identified by the reactions that the compound undergoes, or by spectroscopy (infrared, ultraviolet, NIVIR, and mass spectroscopy). A somewhat simpler situation arises in drug identification. The scope of the problem is more limited here and the chemist working in a hospital trying to identify the source of a drug overdose, or the forensic officer trying to identify a suspected illicit drug or a poison, usually has some prior clues to work with. So does the medicinal chemist working for a pharmaceutical manufacturer who might be trying to discover why a competitor's product is better. As an example, consider a drug overdose case. The patient is brought into the emergency ward of a hospital. This person may either be in a coma, in a hyper excited state, having an allergic reaction, or clearly be hallucinating. These physiological symptoms are themselves clues to the nature of the drug. Often samples of the drug may be found in the patient's possession. Correct medical treatment may require a rapid and accurate identification of a drug powder or capsule. If the patient is conscious, the necessary information is may elicited directly; if not, an examination of the drug is required. If the drug is a tablet or capsule, the process is often simple, since many drugs are coded by a manufacturer's trademark or logo, by shape (round, oval, bullet shape etc.), by formulation (tablet, gelatine capsule etc.) and by colour. A powder is more difficult to identify but under some circumstances it may be easy. Plants drugs are often easy to identify since they contain microscopic bits and pieces of the plant from which they were obtained. This cellular debris is often quite characteristic for certain types of drugs, and they can be identified on this basis alone. A microscope is all that is required. Sometimes chemical colour tests may be used as a confirmation. Certain drugs give rise to characteristic colours when treated with special reagents. If the drug itself is not available and the patient is unconscious or dead, the identification may be more difficult. It may be necessary to pump the stomach or bladder contents of the patient or corpse, to obtain a blood sample, and to work on these. These samples of stomach fluid, urine, or blood would be extracted with an appropriate organic solvent, and the extract would be analysed. Often the final identification of a drug hinges on some type of chromatography. Thin layer chromatography is often used. Under specified conditions, many drug substances can be identified by their R1 values and by the colours that their TLC spots turn when treated with various reagents, or when they are observed under certain visualisation methods. In the experiment, which follows, is used in a simple examination of these techniques as applied to the analysis of an unknown analgesic drug.