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Quality Control of Medicinal Plants. 1.

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Introduction. Plant materials are used as home remedies, OTC drug products and raw materials for the pharmaceutical industry and represent a substantial proportion of the global drug market. Accordingly the evaluation of medicinal plants is very important. This operation involves the identification of the material and determination of its quality and purity ..

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For the evaluation, there are a number of standards (numerical in nature) which are described in pharmacopoeias and other official publications (WHO manual)..

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Substances as experienced by the senses, including taste, sight, smell, and touch.

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The High Performance Thin Layer Chromatography (HPTLC) equipment.

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Sampling. Considerable care must be exercised to ensure that this sample is truly representative . Methods of sampling are fully described in some pharmacopoeias and in WHO manual. Preliminary examination In the case of whole drugs macroscopical and sensory characters are usually sufficient to enable the drug to be identified..

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Foreign matter. This applies to such important drugs as senna leaflets, senna pods, chamomile flowers, ginger, nutmegs and rhubarb. It is always difficult to obtain vegetable drugs in an entirely pure condition, so pharmacopoeias state the permitted percentage of other parts of plant or of other organic matter. However, no poisonous, dangerous or otherwise harmful foreign matter or residue can be allowed..

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Foreign matter is material consisting of any or all of: Parts of the medicinal plant materials other than those named. Any organism , part or product of an organism , other than that named in the specification and the description. Mineral admixture such as soil, stones, sands and dust..

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Determination of foreign matter. Macroscopic examination can conveniently be employed for determining the percent of foreign matter in whole or cut plant materials. However, microscopy is indispensable for powdered materials. In case of whole drugs a weighed quantity (100-500 g, according to the type of drug), of a carefully taken sample is spread in a thin layer on paper. It is examined at x6 magnification and the foreign matter is picked out and weighed and the percentage is recorded..

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Moisture content. Moisture in conjunction with temperature will lead to the activation of enzymes and provide suitable conditions to the proliferation of living organisms. All drugs are at risk of decaying if the humidity in the drug material exceeds 15%. However, different levels of moisture are acceptable for each drug..

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Determination of moisture. The moisture content is especially important for material which absorbs moisture easily or deteriorates quickly in the presence of water, as in cases of drugs containing glycosides (cleavage of glycosidal linkage ). Gravimetric method based on the loss on drying. Separation and measurement of moisture. Chemical methods Spectroscopic methods.

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Loss on drying Direct drying: heating a sample of the drug at 100-105 o C until the weight becomes constant. Although the loss in weight principally is due to water, small amounts of other volatile materials will also contribute to weigh loss, so this method is suitable for drugs containing little or no volatile material as digitalis and aloes..

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Loss on drying Some food stuffs contain substances as fructose , that can be decomposed by heating at 100 o C under atmospheric pressure, such material should be dried in vacuum oven (reduced pressure) at 70 o C. For materials containing considerable amount of volatile material such as balsams, the drying is accomplished by spreading thin layers of weighed drug over glass plates and placing in a desecrator over phosphorous pentoxide under atmospheric or reduced pressure..

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A substance is heated until no more weight is lost, that is, it is completely dry. % Loss on drying (LOD) = W start - W dry/ W start * 100.

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Separation and measurement of moisture. The “loss on drying” methods can be made more specific for the determination of water by separating and evaluating the water obtained from a sample. This can be achieved by passing a dry inert gas through the heated sample and using an absorption train (specific for water) to collect the water carried forward..

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Methods based on distillation The sample to be analyzed is placed in a flask together with a suitable water saturated immiscible solvent ( Toluene , xylene, carbon tetrachloride) and a pieces of porous pot and is distilled. The water in the sample co-distills with the solvent, condensing in the distillate as an immiscible layer..

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Distillation method. These devices permit the direct measurement of the water obtained and the less dense solvent ( Toluene , xylene in device A) is continuously returned to the distillation flask. This method is employed for some volatile oil containing drugs (chamomile flowers, Peppermint and sage leaves). Device B for solvents heaver than water..

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Distillation method. To accommodate the loss of water due to solubility in the solvent, the BP specifies a pre liminary distillation of the solvent with added water ( about 2 ml ); the exact volume of water separating as a layer is read off and then the drug added to the flask and distillation resumed. Water separated from the drug is calculated from the combined final volume. The disadvantage of this method is the requirement of relatively large quantities of the sample..

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Gas chromatographic methods. GC methods are important for moisture determination because of their specificity and efficiency. The water in the weighed, powdered sample can be extracted with dry methanol and an aliquot submitted to chromatography on a suitable column . The water separated by this means is readily determined from the resulting chromatogram. Chemical methods Karl Fischer procedure is the most extensively employed chemical method for water determination. It is used for expensive drugs and chemicals containing small quantities of moisture..

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Karl Fischer procedure. The reagent consists of a solution of iodine , sulphur dioxide and pyridine in dry methanol. This is titrated against a sample containing water , which causes a loss of the dark brown color. At the end point when no water is available, the color of the reagent persists. The basic reaction is a reduction of iodine by sulphur dioxide in the presence of water..

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The reaction goes to completion by the removal of sulphur trioxide as pyridine sulphur trioxide , which in turns reacts with the methanol to form the pyridine salt of methyl sulphate . For crude drugs such as digitalis the powdered material can first be exhausted of water with a suitable anhydrous solvent ( dioxan ) and an aliquot taken for titration..

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Measurement of the electric current produced by the titration reaction.

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To eliminate the interference from atmospheric moisture, the titration is carried out under an atmosphere of dry nitrogen..

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Karl Fischer Apparatus. _bhb. 24.

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Spectroscopic methods. Water will absorb energy at various wave-lengths throughout the electromagnetic spectrum and this fact can be made a basis for its quantitative determination. Measurements can be made in both infrared and ultraviolet regions; interfering substances must be absent. The method is particularly suitable for very small quantities of water (trace quantities in gases). Nuclear magnetic resonance (NMR) spectroscopy has been employed for the determination of moisture in starch, cotton and other plant products..

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Extractive values. 26.

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soxhlet2. Extractive values. The determination of water-soluble or ethanol-soluble extractive is used as a means of evaluating drugs , the constituents of which are not readily estimated by other means. In certain cases extraction of the drug is by maceration, in others by a continuous extraction process ( Soxhlet extractor). The extract of a certain amount of the drug is then evaporated, dried and weighed..

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Extractive values. 28. Eil•l I, Soxhlet continuous extraction apparatus- A, poudered drug for extraction in thimble and plugged with suitable fibre deåtted tow or cotton WNI; solvent refll-mes into thimble and svphons into flask B, containing boiling solvent, receiver is frill. II, Three-stage continuous extracticm md solvent left, extraction by boiling with solvalt; centre, stage; right, removal of solvent. A, sample for extraction; A1, drug; B, soltent; Bl, ræovered soll,ent; C, solvent Qntaining soluble plant constituents; D, final extract (Soxtec Systan, Tecator Ltd.).

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Ash values. When vegetable drugs are incinerated, the organic matter is burnt away and an inorganic residue is left, which is known as ash. The ash figure for each drug is considered as a general measure of quality and it is usually given for each drug in the pharmacopeia. The ash determinations are useful for detecting law-grade products, exhausted drugs and excess of sandy or earthy matter especially in powdered drugs. The pharmacopeias use different types of ash figure as total ash, acid-insoluble ash and water-soluble ash..

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The total ash method is designed to measure the total amount of material remaining after ignition. This includes both ‘physiologic ash’, which is derived from the plant tissue itself, and ‘non- physiologic ash’, which is the residue of the extraneous matter (e.g. sand and soil) adhering to the plant surface..

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31. 40. abstract.

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Acid-insoluble ash. Acid-insoluble ash is the residue obtained after boiling the total ash with dilute HCl and igniting the remaining insoluble matter . This measures the amount of silica present, especially as sand and siliceous earth . A high acid-insoluble ash in drugs such as senna , cloves, and licorice indicates contamination with earthy material ..

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Water-soluble ash. Water-soluble ash consists mainly of the water soluble oxides and carbonates of sodium and potassium..

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. Crude fiber. Crude fiber determinations are used to detect excessive amounts of woody matter in powdered drugs. It is a measure of the content of the particles which resist the effect of dilute mineral acids and dilute alkali such as sclereids , vessels and fibres . It is particularly useful for rhizomes as ginger which contain relatively large amounts of oleoresin and starch..

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The technique involves defating the powder and boiling in turn with standard acid and alkali. The crude fibre so obtained can also be employed quantitatively to assay the fibre content of foods and to detect excess of certain materials in powdered drugs, e.g. clove stalk in clove..

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36. Determination of volatile oil.

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Determination of volatile oil. Minimum standards for the percentage of volatile oil present in a number of drugs are prescribed by many pharmacopeias. A distillation method is usually employed using a suitable apparatus. The recovery of the distillate is collected in the graduated tube which already contains a known amount of xylene ( European Pharmacopoeia, WHO manual). Vol. of volatile oil = total vol.- vol. of xylene.

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i" plant drugs. 38.

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Tannin content. Tannins are substances capable of turning animal hides into leather by binding proteins to form water-insoluble substances that are resistant to proteolytic enzymes. This process, when applied to living tissue, is known as an “ astringent” action and is the reason for the therapeutic application of tannins..

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Tannins (polyphenols) are easily oxidized and polymerized in solutions; if this happens they lose much of their astringent effect. A few drugs are assayed for their tannin content. The method refers to those polyphenols adsorbed by hide powder and giving a color reaction with sodium phospho molybdo tungstate reagent ..

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Bitterness value. Medicinal plant materials that have a strong bitter taste (bitters) are employed therapeutically, mostly as appetizing agents. Their bitterness stimulates secretions in the gastrointestinal tract, especially of gastric juice. Bitter substances can be determined chemically..

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However, science they are mostly composed of two or more constituents with various degrees of bitterness, it is first necessary to measure total bitterness by taste . The bitterness value is determined organoleptically by comparison with a quinine hydrochloride solution which acts as the standard..

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Swelling index. This is defined in the BP as the volume in milliliters occupied by 1 g of a drug, including any adhering mucilage, after it has swollen in an aqueous liquid for 4 h. The drug (cut or whole) is treated with 1 ml of ethanol (96%) and 25 ml water in a graduated cylinder , shaken every 10 min for 1h and allowed to stand as specified. The standard can be determined on the whole drug (linseed and psyllium ) or on the powder (marshmallow root)..

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R f values. Pharmacopoeias are increasingly employing thin-layer chromatography as a means for assessing quality and purity. The R f value ( rate of flow, distance moved by solute divided by distance moved by solvent front) of a compound, determined under specific conditions, is characteristic and can be used as an aid to identity..

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Q uantitative extracts of crude drugs are prepared and compared chromatographically with standard reference solutions of the known constituents. In an analogous manner, GC retention times and peak areas can be employed for the examination of volatile oils and other mixtures..

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Gas chromatography Is the most suitable analytical method ( qualitative and quantitative analysis). injector Gas Chromatography O.•c.m detecto oven.

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Thank You. 47.