Evaluation Of Crude Drugs.

Evaluation Of Crude Drugs.

Definition: -

  • Confirmation of identity and determination of quality and purity of crude drugs is called as evaluation of crude drugs.
  • Besides confirmation of identity and determination of quality and purity the term drug evaluation also covers detection and determination of the type of adulteration present.
Methods of Evaluation: -
  1. Organoleptic evaluation.
  2. Microscopic evaluation.
  3. Chemical evaluation.
  4. Physical evaluation.
  5. Biological evaluation.

1) Organoleptic evaluation: -

  • Examination of the drug by color, odor, shape size, taste, touch, texture, and sound is known as Organoleptic evaluation.

  • e.g. taste of fennel is sweet. Taste of clove is pungent. Leaf of datura is hairy.
  • While evaluating by this method there are certain restrictions like changes in shape & size of drugs during drying & packing so it is Difficult to the study the drug by organoleptic evaluation.
  • e.g. length of the cinnamon quill is 1 meter but mostly it is found in small pieces in the market.
  • Digitalis leaves crumple in small pieces during drying and packing.

2) Microscopic Evaluation: -

  • Every species has a unique anatomy, the study of which helps us in their identification process.
  • Microscopic evaluation is useful for the organized drugs (i.e. drugs having cellular structure). T. S. & L.S. of the drugs are observed under the microscope.
  • T. S. & L.S. of the drugs are studied under the microscope with the help of the staining agent.
  • Special attention is given to the type of tissues, their arrangement, presence or absence of special substances like calcium oxalate crystals, starch grains, size and shape of starch grains, cell contents etc.
  • e.g. Nux vomica have lignified trichomes, Fennel contains vascular bundles which are surrounded by reticulated parenchyma and shows the presence of vitae which secrete volatile oil.
  • Microchemistry: Sometimes small quantities of chemical reagent are used on sections to highlight specific cells or structures.
  • e.g. If we want to observe starch grain then we have to use dilute iodine solution the area of T. S. containing starch grains becomes blue due to iodine.
  • To locate strychnine & Brucine in Nux- vomica seeds, we use ammonium vanadate.
  • Thus the use of small quantities of drugs & chemical reagents in microscopy is known as microchemistry.
  • Following are the examples of microscopic evaluation. (Leaf constants)
  • A) Stomatal No. : - It is an average no. of stomata present in 1 sq. mm of the epidermis.
  • The total no is constant for a given drug. e.g Drug Stomatal no. Datura stramonium 87, D.innoxia 141.
  • B) Stomatal Index: - It is the percentage which the number of stomata forms to the total no. of epidermal cells, each stoma being counted as one cell.
  • I = S *100/(E+ S ) (where I = Stomatal Index. S = No of stomata. E = No of epidermal cell in the same area.)
  • The stomatal index is useful for evaluation of leaf drug however, it is a constant for a given species.
                DrugStomatal index
       Indian senna17 to 20
        Alexandrian senna10.8 to 12.6

  • Vein islet no
    : - Islet is the area surrounded by veins.
  • Vein Islet no.: " It is the no. of vein islets per sq.mm of leaf surface.
  • It is constant for given species of drug It is used for evaluation of crude drug
  • e.g.
  • DrugVein islet no
    Indian senna19 – 23
    Alexandrian senna25 – 30
  • Palisade ratio: - It is the average no of palisade cells beneath one epidermal cell using four continuous epidermal cells for the count.
  • It is constant for given leaf and used for evaluation of leaf.
  • e.g.
                  Digitalis purpurea                                         3.7      to 4.2 
                  Datura stramonium                                      4         to 7
                  Atropa belladonna                                       6          to 10

3) Quantitative Microscopy: (Lycopodium Spore Method):-

  • It is an important analytical technique for powder drugs, especially when chemical and another method of evaluation of crude drugs fail as an accurate measure of quality.
  • Lycopodium spores are very characteristic in shape and appearance and exceptionally uniform in size (25 mm).
  • On an average, 94000 spores per mg of powdered Lycopodium are present.
  • A powdered drug is evaluated by this technique, if it contains:
1) Well defined particles which may be counted, e.g. Starch grains or pollen grains,
2) Single layered cells or tissues, the area of which may be traced to suitable magnification and actual area calculated or,
3) The object of uniform thickness, the length of which can be measured under suitable magnification and the actual area calculated.
  • The size of starch grains is also important for the detection of adulterants.
  • In the case of Cinnamomum cassia, the diameter of starch grains is usually more than 10 microns. The dimension of fibers also helps in detecting adulteration in the case of Cinnamon.
  • The number of sclerenchymatous cells per square cm in cardamom is one of the criteria for the detection of varieties of cardamom seed in powdered form.

4) Chemical Method Of Evaluation: -

  • This method of evaluation consists of isolation, purification & identification of the active chemical constituent from the crude drug.
  • This method consists of following test 1.Acid value 2.saponification value 3.Iodine value 4.Ester value 5.Acetyl value, and 6.Determination of methoxy group.
  • Chemical evaluation also consists of titration, gravimetric analysis, chromatographic analysis, spectrophotometer analysis, etc.
  • Chemical tests are also helpful for the identification of crude drugs. e. g.
1.Van urk's test for Ergot. 2. Halphenes test for Arachis oil. 3. Borntrager tests for Anthraquinone Glycoside.
Ex. Starch gives blue color with iodine. It forms a thick viscous solution with water.
  • The estimation of chief constituents or group of active constituents is an integral part of chemical evaluation e.g. total sennosides in senna, morphine in opium, citral in lemongrass oil etc.
  • The chemical tests also help in proper identification of varieties of the crude drugs eg. the solution of lead acetate or lead subacetate is used specifically for chemical identity of gums.

5) Physical Method Of Evaluation: -

  • Following are methods of physical Evaluation.
  • A) Determination of moisture content
  • B) Determination of Viscosity
  • C) Determination of Melting point.
  • D) Determination of Optical rotation.
  • E) Determination of Refractive Index
  • F) Determination of ash content
  • G) Determination of Extractives
  • H) Determination of volatile oil content
  • Physical methods are used for evaluation wherever they are possible.
A)        Moisture content determination: -
  • The % of active chemical constituents is always given on an air-dried basis of the drug.
  • A simple method to calculate is weighing drug and comparing the weight after placing in desiccator for 15 mins.

  • Moisture content is determined by heating the drug in an oven at 1050c till constant weight.
  • The drugs which contain volatile oil their, moisture content is determined by Toluene distillation method.
  • The excess moisture is harmful to the crude drugs because in it’s presence chemical constituent of drug get hydrolyzed.
  • If drug contains excess moisture bacteria, fungi, insects attack drug & cause deterioration.
  • Drug                                       Moisture content % W/W
  • Aloe                                        Not more than 10 % W/W
  • Digitalis                                  Not more than 5 % W/W
  • Starch                                    Not more than 15 % W/W
B) Determination of viscosity: -
  • The viscosity of a liquid is constant at a given temp.
  • Viscosity is an indication of the purity of the drug.
  • It is determined, at 250C, by using any viscometer the common one is "Ostwald Viscometer" the viscosity of liquid paraffin should not be less than 64-centimeter stokes.
  • It is particularly important to detect purity of certain drugs like Honey, Castor Oil, Shark Liver Oil etc.
C) Determination of melting point: -

  • It is one of the criteria to determine quality and purity of crude drugs.
  • Crude drugs Contain number of chemicals, therefore, their melting point is not sharp but it is in a range. Ex.
  • Drug                                                               Melting point
  • Hard paraffin                                                 50 - 570c
  • Beeswax                                                       62 - 650 c
  • Cocoa Butter                                                 30 - 330 c
  • Colophony                                                    75 - 850 c
D) Determination of optical rotation:-

  • Optical rotation is determined by the polarimeter certain crude drugs can rotate plane Of polarized light to right (dextrorotatory drug) or to left (laevorotatory drugs.).
  • It is determined by using sodium vapor lamp at 250 c. optical rotation is one of the criteria to determine the quality & purity of the drug.
  • Name of drug                                              Angle of optical rotation
  • Honey                                                                        + 30     to -150
  • Clove oil                                                                         0     to  -1.50
  • Caraway oil                                                               + 70    to + 800
E) Refractive Index: -

  • When a ray of light passes from one medium to another of different density it bends from the original path.
  • Thus the ratio of the velocity of light in the vacuum to its velocity in substance is termed as refractive Index of substance.
  • Refractive index varies with the wavelength of the light.
  • Drugs                                                 Refractive Index
  • Arachis oil                                          1.4678 to 1. 4698
  • Clove oil                                             1.5300 to 1. 5310
F) Ash content: -

  • The residue remaining after incineration (burning) is known as ash content of the drug.
  • The ash represents inorganic chemicals, Salt & soil attached to the drug.
  • It is a criterion to determine quality & purity.
  • Drug                                                   Total ash
  • Aloes                                                  5  % W / W
  • Cannabis                                           15% W / W
  • Ginger                                                6  % W / W
  • Acid insoluble ash is the part of total ash, which is insoluble in dilute hydrochloric acid.
  • Soil & sand attached to the drug is determined by acid insoluble ash content.
  • Useful for drugs where soil contamination is very common.
  • Drugs                                                 Acid insoluble ash
  • Cannabis                                           Not more than 5 % W / W
  • Cardamom                                        Not more than 3.5 % W / W
  • Agar                                                    Not more than 1% W / W
G) Extractives: -
  • Extract value is criteria to determine quality and purity of the crude drug.
  • Different types of Solvents are used to prepare extracts of the crude drug because different chemicals are soluble in the different solvent.
  • The solvent is evaporated and weight of extractive is determined.
  • There are following types of extractives.
  • a) Water soluble extractive: - Water is a good solvent for sugar, mucilage, plant acids, it is used for those drugs, which contains chemicals. Ex.
  • Drug                                                   Water-soluble extractives.
  • Aloes:                                                 Should not be less than 25 % W / W
  • Senna leaves                                   Should not be less than 30 % W / W
  • Ginger                                                Should not be less than 10 % W / W
  • b) Alcohol soluble Extractives: - Alcohol is a good solvent for resins, tannins, it is used for the drug which contains tannins.
  • Generally, 95% ethyl alcohol is used for determination of alcohol soluble extractives.
  • Sometimes dilute alcohol may be used according to the solubility of chemicals of drugs.
  • Drugs                                    Alcohol soluble extractives
  • Benzoin                                 Not less than 90 % W / W
  • Asafoetida                             Not less than 50 % W / W
  • Ginger                                    Not less than 4.5 % W / W
H) Determination of volatile oil content: -
  • Several drugs contain volatile oil for determination volatile oil content or % of volatile oil by kjeldol distillation method or Toluene distillation method.
  • Drug                                         Volatile oil content(% W/W)Not less than
  • Fennel                                                           1.4 % W / W
  • Cardamom                                                    4    % W / W
  • Caraway                                                        2.5 % W / W

Different chromatographic techniques such as thin layer chromatography (TLC) high-performance liquid chromatography (HPCL), gas chromatography, column chromatography, gel permeation chromatography, affinity chromatography, as well as techniques like spectrophotometric method, radioimmunoassays are used very frequently for physical evaluation of crude drugs.


  • The biological assay is performed for those drugs which can not be tested properly in the laboratories. They are performed on 1) cells. 2) Bacteria. 3) Fungi. 4) Animals. Etc.
  • This method is used for antibiotics, vitamins, hormones & cardiac glycosides.
  • Bioassay is the measurement of the sample drugs, which produce the same biological effect as that of standard preparation such activity is represented in "International units" (I. U.)
  • e.g. Digitalis 1 I.U. is contained 76mg of the standard preparation.
  • Vit A – 1 I. U. contained in 0.344 mg of the standard preparation.

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