Chemical Evaluation

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Chapter: Pharmacognosy and Phytochemistry : Evaluation of Crude Drugs

The chemical evaluation includes qualitative chemical tests, quantitative chemical tests, chemical assays, and instrumental analysis. The isolation, purification, and identification of active constituents are chemical methods of evaluation. Qualitative chemical tests include identification tests for various phytoconstituents like alkaloids, glycosides, tannins, etc.


CHEMICAL EVALUATION

 

 

The chemical evaluation includes qualitative chemical tests, quantitative chemical tests, chemical assays, and instrumen-tal analysis. The isolation, purification, and identification of active constituents are chemical methods of evaluation. Qualitative chemical tests include identification tests for various phytoconstituents like alkaloids, glycosides, tannins, etc. The procedures for the identification tests of various phytoconstituents are given under their respective chapters in the text, where it could be referred. Examples of identification of constituents are: copper acetate used in the detection of colophony present as an adulterant for resins, balsams, and waxes; Holphen’s test for cottonseed oil and Baudouin’s test for sesame oil in olive oil; the test with acetic and nitric acids for Gurjun balsam in copaiba; Van Urk’s reagent for ergot; Vitali’s morins reaction for tropane alkaloids; iodine for starch; murexide test for purine bases, etc. are examples of this evaluation.

 

Quantitative chemical tests such as acid value (resins, balsams), saponification value (balsams), ester value (balsams, volatile oils), acetyl value (volatile oils), etc. are also useful in evaluation of a drug by means of chemical treatment.

 

Chemical assays include assays for alkaloid, resin, volatile oil, glycoside, vitamins, or other constituent. Few examples are the assay of total alkaloid in belladonna herb, the total alkaloid and nonphenolic alkaloid in ipecacuanha, the alkaloid strychnine in nux vomica, the resin in jalap, and the vitamins in cod-liver oil. The results obtained can conclude the presence of inferior or exhausted drug and, by proving absence of the assayed constituent, it will suggest complete substitution of a worthless article.

 

Instrumental analyses are used to analyse the chemical groups of phytoconstituents using chromatographic and spectroscopic methods. Chromatographic methods include paper chromatography, thin-layer chromatography, gas chromatography, high-performance liquid chromatography, and high-performance thin-layer chromatography. Spectroscopic methods include ultraviolet and visible spectroscopy, infrared spectroscopy, mass spectroscopy, and nuclear magnetic spectroscopy.

 

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