EVALUATION OF CRUDE DRUGS:
Definition of evaluation
Evaluation of crude drug means determination of identity, purity and quality of a drug. Evaluation of crude is most important to know whether the drugs are adulterated with other substance or not. Before using any crude drug it must be checked for its quality and purity.
Methods of evaluation
There are five methods for evaluating crude drug for its quality and purity by considering morphological, physical and chemical characteristics.
? Organoleptic evaluation
? Anatomical evaluation
? Physical evaluation
? Chemical evaluation
? Biological evaluation
It includes the study of morphology and sensory characters. Two types are present
1. Sensory characters
2. Gross features
Size and Shape, Colour, Texture, Odour and Taste are useful in the evaluation of drugs.
Size and shape:
Each and every plant has its own shape for its fruits, leaves. And even a particular size is present.
Shape: Tragacanth- ribbon shaped,
Acacia- ovoid tear shaped.
Each and every crude drug or plant has its own color for its flowers, fruits and seeds.
Cardamom- green colour fruit
Cinnamon- brown color bark
Turmeric-yellow colour powder
Each and every plant has its own texture for better identification.
Fractured surface- cinchona.
The odour of the drug may be either definite or indefinite. But by odour it’s easy to identify few compounds very easily.
Ginger, capsicum-pungent odour.
For each and everything there will be a specified taste.
Gross features: it includes the visual examination of the plant.
? Barks Ex: Cinnamon, Cinchona
? Underground structures Ex: Ginger, Turmeric
? Leaves EX: Senna leaves
? Flowers Ex: Saffron
? Fruits Ex: Almond, Amla
? Seeds Ex: Linseed, Vomica
? Herbs Ex: Gingko biloba
This method allows a more detailed examination of a drug and it can be used to identify organised crude drugs by their known histological characters. Before examination through a microscope the material must be suitably prepared .This can be done by powdering or cutting thin sections of the drug or preparing a macerate. Microscope can also be used for a quantitative evaluation of crude drugs and adulterated powders.
This is done by counting the specific histological appearance such as,
(a) Leaf constants
(d) Calcium oxalate crystals
(e) Quantitative microscopy
(a) Leaf constants:
? Stomatal Number
? Stomatal Index
? Vein-islet Number
? Palisade Ratio
Stomatal number is defined as the average number of stomata present per square millimeter of the epidermis is known as stomatal number. Stomatal number is relatively constant for a particular species of same age.
Example: Datura – 141 (upper epidermis)
The percentage proportion of the number of stomata to the total number of epidermal cells is known as stomatal index. Stomatal index is relatively constant for any given species.
Example: Atropa – 20.0-23.0 (lower epidermis)
The term “vein-islet” is used for the minute area of photosynthetic tissue encircled by the ultimate divisions of the conducting strand. The number of vein-islets per sq.mm of leaf surface is known as vein- islet number. It is constant for a given species of the plants. It is irrespective with the age factor of plant.
Example: Cassia senna (26).
The average number of palisade cells beneath one epidermal cell, using four continuous epidermal cells for the count is knowm as palisade ratio. It is determined from powdered drugs using camera lucida.
Example: Atropa belladonna – 06-10
Stomata: primary and important function of stomata is gaseous exchange
It is a minute epidermal opening present on the aerial parts of plants, with following characteristics:
A central pore
Two kidney shaped guard cells
The secondary function of stomata is transpiration. It is not an essential part of plant e.g. bryophytes and submerged plants do not have stomata. These stomata majorly present in green parts than in roots. These stomata is present all over the plant i.e. in ephedra we find stomata in stem, in clove we find stomata in flowers. Stomata are abundantly present in dicot plants. These are present on upper and lower parts of leaves but great variations in number.
Types of stomata: Depending upon the type of the guard cells and arrangement of subsidiary cells, stomata are divided in to 4 types. They are:
1. Moss type
2. Gymnospermous type
3. Gramineous type
4. Dicotyledonous type
These dicotyledonous stomata are of five types again. They are:
(e) Radiate- celled
(a) Rubiaceous: this type of stomata comprises of two guard cells covered by two subsidiary cells, the long axes of which are parallel to that of stomata example is: coca, senna.
(b) Caryophyllaceous: The guard cells are covered by two subsidiary cells, as in case of rubiaceous stomata, but the arrangement of subsidiary cells on the guard cells is at right angle to that of stomata, examples is peppermint, vasaka.
(c) Cruciferous: The number of guard cells is two, as in all other cases. But, the guard cells are covered by three subsidiary cells, which one is markedly smaller than other two stomata, example is stramonium, datura
(d) Ranunculaceous: In this type, stomata are surrounded by varying number of subsidiary cells resembling other epidermal cells. Example is buchu, digitalis.
(e) Radiate- celled: The two guard cells are surrounded by a circle of radiating subsidiary cells.