QUALITY CONTROL OF CRUDE DRUGS: A TEACHER’S COMPREHENSIVE GUIDE
Welcome, future pharmacognosists and quality control professionals!
Quality control of crude drugs is one of the most critical aspects of pharmacognosy. It ensures that the natural products used as medicines are safe, pure, and effective. As a pharmacognosy educator with years of experience teaching quality control of natural products, I have observed that students often underestimate the complexity of adulteration and the importance of proper drug evaluation. Let me tell you: Quality control is what separates genuine medicines from harmful adulterants.
In this comprehensive guide, I will walk you through the complete quality control of crude drugs—adulteration and its methods, organoleptic, morphological, microscopic, physical, chemical, and biological evaluation. By the end of this article, you will have a thorough understanding of how to ensure the quality, purity, and safety of crude drugs. Let us begin!
Dpharmguru’s exam insights:
Quality control of crude drugs is frequently tested in pharmacognosy exams. Remember: Adulteration can be intentional or unintentional. There are six methods of drug evaluation—Organoleptic, Morphological, Microscopic, Physical, Chemical, and Biological. Leaf constants (Palisade Ratio, Vein-Islet Number, Stomatal Number) are important microscopic parameters. Lycopodium spore method is used for quantitative microscopy. These are classic exam questions!
3.1. ADULTERATION OF CRUDE DRUGS
3.1.1. Definition
Drug degradation by an adulterant (a substance resembling the genuine drug morphologically as well as organoleptically) is termed as adulteration. However, the adulterant lacks the active constituents of the genuine drug. Adulteration disrupts the drug quality.
A drug can be adulterated by introducing impurities, removing the active constituents either completely or partially, or by adding low-grade and spoiled drugs or totally different material which resembles the genuine drug being substituted.
Adulteration can also be defined as admixture or substitution of genuine drugs with spurious, inferior, defective, useless, or harmful substances.
The corrupt dealers practice adulteration when the supply of drug becomes limited or when the price of drug is high. However, if appropriate conditions of collection, transportation, and identification are not maintained, accidental adulteration can occur, which is termed as undeliberate/unconditional adulteration.
Adulteration Involves:
- Deterioration: Impairment in drug quality
- Admixture: Accidental addition of one object into another due to ignorance or carelessness
- Sophistication: Intentional type of adulteration
- Substitution: Addition of an entirely different substance instead of the original drug
- Inferiority: Addition of any substandard drug
- Spoilage: Occurs as a result of microbial attack
3.1.2. Different Methods of Adulteration of Crude Drugs
Adulterants or adulteration types can be categorised as:
- Unintentional Adulteration: Occurs due to ignorance, carelessness, or lack of knowledge
- Intentional Adulteration: Deliberate adulteration for profit
3.1.2.1. Unintentional Adulteration
- Name Confusion: Similar names cause interchange (e.g., Parpatta = Fumaria parviflora; Parpadagam = Mollugo pentaphylla)
- Lack of Knowledge about Authentic Source: Nagakesar from Mesua ferrea adulterated with Calophyllum inophyllum
- Similarity in Morphology: Mucuna prurients adulterated with M. utilis, M. deeringiana, Canavalia virosa
- Lack of Authentic Plant: Hypericum patulum sold as H. perforatum in India
- Similarity in Colour: Ratanjot from Arnebia euchroma substituted for Ventilago madraspatana
- Careless Collections: Parmelia perlata admixed with P. perforata, P. cirrhata, and Usnea sp.
- Unknown Reasons: Vidari from Pueraria tuberosa substituted with Cycas circinalis
3.1.2.2. Intentional Adulteration
- Using Manufactured Substances: Artificial materials resembling drugs (e.g., flour dough for ergot, bass-wood for nutmeg, paraffin wax for beeswax)
- Substitution Using Inferior Commercial Varieties: Similar but inferior drugs (e.g., hog gum for tragacanth, Arabian senna for senna)
- Substitution Using Exhausted Drugs: Extracted drugs re-coloured/reframed (e.g., exhausted clove, fennel, saffron)
- Substitution of Superficially Similar Inferior Natural Substances: Morphologically similar but different drugs (e.g., ailanthus leaves for belladonna, safflower for saffron)
- Using Vegetative Parts of Same Plant: Excessive stems, mosses, liverworts mixed with drugs
- Addition of Toxic Materials: Stones, lead shot, glass pieces added to drugs
- Adulteration of Powders: Powdered waste products mixed (e.g., olive stones, brick powder)
- Addition of Synthetic Principles: Synthetic actives added (e.g., citral in lemon oil, sildenafil in herbal products)
3.2. EVALUATION OF CRUDE DRUGS
A drug is evaluated for identifying it, determining its quality and purity, and detecting the type of adulteration.
Crude drug evaluation is required for studying:
- Biochemical variation a drug undergoes
- Deterioration while being treated and during storage
- Substitution and adulteration due to carelessness, ignorance, or fraud
A drug can be evaluated by the following six methods:
- Organoleptic evaluation
- Morphological evaluation
- Microscopic evaluation
- Physical evaluation
- Chemical evaluation
- Biological evaluation
3.2.1. Organoleptic Evaluation of Crude Drugs
Organoleptic examination involves analysis of the substance via human senses—taste, smell, touch, and sight.
- Colour: Can differ based on species, processing, and storage
- Texture: Stickiness, brittleness, smoothness, or roughness
- Shape and Size: Quality and consistency assessment
- Aroma: Pleasant, earthy, floral, or pungent—helps detect adulteration
- Flavour: Astringent, sour, sweet, or bitter—connected to medical benefits
3.2.2. Morphological Evaluation of Crude Drugs
Barks: Woody stem tissues (e.g., cinnamon, cinchona, quillaia). Shapes include flat, curved, channelled, quill, double quill, and compound quill.
Underground Structures: Roots, rhizomes, and stolons. Shapes include cylindrical, conical, fusiform, and oval.
Leaves: Simple and compound leaves. Shapes include acicular, elliptical, oval, oblong round, round, linear, lanceolate, and ovate.
Flowers: Calyx, corolla, androecium, and gynoecium. Inflorescences are also studied.
Fruits: Globular, oblong, or ellipsoidal (e.g., cardamom, colocynth, bael).
Seeds: Characterised by hilum, micropyle, and raphe. Shapes include ovate, spherical, oval, reniform, and planoconvex (e.g., ispaghula, linseed, nux-vomica).
Sensory Characters: Colour, smell, taste, and texture. Drugs with volatile oils have characteristic odour. Taste may be pungent (capsicum), bitter (gentian), or sweet (glycyrrhiza).
3.2.3. Microscopic Evaluation of Crude Drugs
Microscopic evaluation aids in comprehensive examination of a drug and can be used to identify organised medicines based on their recognised histological characteristics.
Stains and Reagents:
- Phloroglucinol + HCl: Red stain with lignin
- Ruthenium Red: Mucilage turns pink
- N/50 Iodine solution: Starch and hemicellulose turn blue
- Corallin soda + Sodium carbonate: Cellulose swells and dissolves
3.2.3.1. Leaf Constants
- Palisade Ratio: Number of palisade cells per epidermal cell
- Vein-Islet Number: Number of vein-islets per sq mm of leaf surface
- Vein-Termination Number: Number of veinlet terminations per sq mm
- Stomatal Number: Average number of stomata per sq mm of leaf epidermis
- Stomatal Index (S.I.): S.I. = S/(E+S) × 100, where S = number of stomata, E = number of epidermal cells
Stomata and Trichomes
Stomata: Minute epidermal openings with guard cells. Primary function is gaseous exchange; secondary is transpiration.
Trichomes: Outgrowths of epidermal cells—tubular, elongated, or glandular. Used as diagnostic features for drug identification.
3.2.3.2. Quantitative Microscopy / Lycopodium Spore Method
Lycopodium spores are of uniform size (~25 μm). About 94,000 spores are found in 1 mg of powdered lycopodium.
Formula for Percentage Purity:
% Purity = (N × W × 94,000 × 100) / (S × M × P)Where: N = Number of characteristic structures, W = Weight of lycopodium (mg), S = Number of lycopodium spores, M = Weight of sample, P = Constant (e.g., 2,86,000 for ginger starch grains)
3.2.4. Physical Evaluation of Crude Drugs
- Moisture Content: Determined by heating at 105°C to constant weight
- Viscosity: Liquid drugs—constant at given temperature
- Melting Point: Purity determination (e.g., Colophony 75-85°C, Beeswax 62-65°C)
- Solubility: Detects adulterants (e.g., alkaloidal bases soluble in chloroform)
- Optical Rotation: Dextrorotatory (+) or Levorotatory (−)
- Refractive Index: Constant for pure liquids
- Ash Values: Total ash, acid-insoluble ash—represents inorganic salts
- Extractives: Water-soluble, alcohol-soluble, ether-soluble extractives
- Volatile Oil Content: Standardisation of aromatic drugs
- Foreign Organic Matter: Maximum limits in monographs
3.2.5. Chemical Evaluation of Crude Drugs
Chemical evaluation involves different chemical tests and assays, including isolation, purification, and identification of active constituents.
3.2.5.1. Qualitative Chemical Examination
- Alkaloids: Mayer’s reagent (cream), Dragendroff’s (orange brown), Hager’s (yellow), Wagner’s (reddish-brown)
- Carbohydrates & Glycosides: Molisch’s test, Fehling’s, Barfoed’s, Benedict’s reagents
- Phytosterols: Liebermann-Burchard’s test
- Fixed Oils & Fats: Oil stain test, saponification test
- Saponins: Foam test, haemolysis test
- Phenolic Compounds & Tannins: Ferric chloride test, gelatin test
- Proteins & Amino Acids: Millon’s, biuret, ninhydrin tests
- Gums & Mucilages: Precipitation with alcohol
- Volatile Oils: Hydro-distillation
3.2.6. Biological Evaluation of Crude Drugs
Bioassay is the measure of the capability of a sample to produce a biological effect in comparison to the standard preparation. Such activity is represented in International Units (IU).
3.2.6.1. Microbiological Assays
- Cylinder Plate Method: Diameter of inhibition zones measured
- Turbidimetric Method: Transmittance of microbial suspensions measured
3.2.6.2. Microbiological Limits (IP)
- Gum Acacia: No E. coli per gram
- Guar Gum: No E. coli, Salmonella; total bacterial count ≤ 5000/gm
- Starch: No E. coli, Salmonella
- Tragacanth: No E. coli, Salmonella
- Dried Yeast: No E. coli, Salmonella
- Gelatin: No E. coli, no Salmonella in 10g sample; total bacterial count ≤ 1000/gm
Dpharmguru’s exam insights:
Biological evaluation and microbiological limits are frequently tested. Remember: Bioassay uses International Units (IU). Cylinder plate and turbidimetric methods are used for antibiotics. Microbiological limits for drugs like Acacia, Guar gum, Starch, and Gelatin are specified in IP. These are classic exam questions!
SUMMARY TABLE: EVALUATION METHODS
| Evaluation Method | Based On | Key Parameters |
|---|---|---|
| Organoleptic | Human senses | Colour, texture, shape, size, aroma, flavour |
| Morphological | Plant parts | Barks, roots, leaves, flowers, fruits, seeds |
| Microscopic | Histological features | Leaf constants, stomata, trichomes, lycopodium method |
| Physical | Physical properties | Moisture, viscosity, melting point, ash values, extractives |
| Chemical | Chemical tests | Alkaloids, glycosides, tannins, volatile oils |
| Biological | Living organisms | Bioassay, microbiological assays |
FREQUENTLY ASKED QUESTIONS (FAQs)
1. What is adulteration of crude drugs?
Adulteration is the degradation of drug quality by adding impurities, substituting with inferior substances, or removing active constituents. It can be intentional (for profit) or unintentional (due to ignorance).
2. What are the six methods of drug evaluation?
The six methods are: Organoleptic, Morphological, Microscopic, Physical, Chemical, and Biological evaluation.
3. What is the Lycopodium spore method?
The Lycopodium spore method is a quantitative microscopic technique used for powdered crude drugs. Lycopodium spores are uniform in size (~25 μm) and about 94,000 spores are present in 1 mg. It is used to calculate the percentage purity of powdered drugs.
4. What is the Stomatal Index?
The Stomatal Index (S.I.) is the fraction of epidermal cells that have undergone stomatal modification. It is calculated using: S.I. = S/(E+S) × 100, where S = number of stomata and E = number of epidermal cells per unit area.
5. What is the difference between total ash and acid-insoluble ash?
Total ash represents the inorganic residue left after incineration—includes both physiological and non-physiological ash. Acid-insoluble ash is the residue insoluble in dilute hydrochloric acid—mainly represents extraneous matter like sand and soil.
6. What are the microbiological limits for crude drugs?
According to IP: Gum Acacia, Starch, Tragacanth, and Dried Yeast should have no E. coli or Salmonella. Guar gum should have total bacterial count ≤ 5000/gm. Gelatin should have total bacterial count ≤ 1000/gm.
SUMMARY
Quality control of crude drugs is essential for ensuring safety, purity, and efficacy. This guide covered:
- Adulteration: Types—intentional and unintentional; methods include substitution, sophistication, admixture, and deterioration
- Organoleptic Evaluation: Using human senses—colour, texture, shape, aroma, and flavour
- Morphological Evaluation: Based on plant parts—barks, roots, leaves, flowers, fruits, seeds
- Microscopic Evaluation: Histological features, leaf constants, stomata, trichomes, and Lycopodium spore method
- Physical Evaluation: Moisture content, viscosity, melting point, ash values, extractives, optical rotation
- Chemical Evaluation: Qualitative tests for alkaloids, glycosides, tannins, saponins, volatile oils
- Biological Evaluation: Bioassay, cylinder plate method, turbidimetric method, microbiological limits
As I always tell my students: “Quality control is the guardian of patient safety. Every drug, whether synthetic or natural, must meet rigorous quality standards before it reaches the patient.”
REFERENCES AND FURTHER READING
- Pharmacy Council of India (PCI). (2022). Pharmacognosy Syllabus. New Delhi: PCI.
- Tyler, V. E., Brady, L. R., & Robbers, J. E. (2020). Pharmacognosy and Pharmacobiotechnology (9th ed.). Wolters Kluwer.
- Trease, G. E., & Evans, W. C. (2019). Trease and Evans’ Pharmacognosy (16th ed.). Elsevier.
- Kokate, C. K., Purohit, A. P., & Gokhale, S. B. (2020). Pharmacognosy (50th ed.). Nirali Prakashan.
- Indian Pharmacopoeia Commission. (2018). Indian Pharmacopoeia (8th ed.). Ghaziabad: IPC.
- World Health Organization (WHO). (2022). Guidelines on Quality Control of Herbal Medicines. Retrieved from https://www.who.int.
Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult qualified healthcare professionals for medical concerns. Pharmaceutical regulations and guidelines may vary by region—always refer to your local regulatory authorities for specific requirements.
written by:
Dr. N. Sujith Kumar
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