Lecture ( 11 D )
4-Physical evaluation
In this evaluation physical standards are to be determined for drugs which is constant for crude drugs ,but may help in evaluation ,these are :
· Moisture content; is determined by heating a drug at 1050C in the oven to constant weight.
· Viscosity of liquid ;is constant at a given temperature & is an index of composition
· Melting point ;it is one of the parameters to judge the purity of crude drugs .
· Solubility; the presence of adulterant in a drug could be indicated by solubility e.g the glycosides are extract with alcohol &water while aglycone are soluble in non polar solvent like benzene.
· Optical rotation ; is determined at 250C using sodium lamp as the source of light .plane of polarized light may be rotated towards right (dextro rotatory ) or towards left (levo rotatory) .
· Refractive index :is the ratio of the velocity of light in vacuum to its velocity in the substance .It s constant for purity drugs at constant temperature.
· Ash values & extractives; ash which is simply represents inorganic salts , naturally occurring in drug or adhering to it as a form of adulteration like sand , oil , calcium oxalate ,chalk powder. Extractives ;various solvents are used for determination of extractives , the solvent used for extraction is in a position to dissolve appreciable quantities of substance
· Volatile oil content ,aromatic drugs is due to their odorous i:e volatile oil content e.g caraway ,dill ,clove , cardamom seed .
· Foreign organic matter ;the limit for foreign organic matter is mentioned for natural drugs of vegetable origin
5-Biological evaluation
It is known also as bioassay ,means the crude drug or sample tested capable of producing biological effect as that of the standard preparation; the activity is represented in units known international unite (I.U). i:e the specific biological activity contained in each I.U e.g Digitalis contained 76mg of standard preparation in one I.U. Bioassay method are mainly three type: a-toxic b-symptomatic &c-tissue methods. Toxic &symptomatic ,the animals are used ,whereas tissue method used isolated organ or tissue.
Spectro photometric methods
(i)Ultra-violet &visible specro photometry:
Measurement of light absorption by substancesin the wavelength region from 190 to 900nm.The region from 190 to 380 is known as the UV region &from 380 to 900nm,the visible region of the spectrum. Absorption in the UV-visible region arises from electronic transitions within the molecule.
(ii)Infra-Red spectroscopy
I.R is the study of the reflected ,absorption or transmitted radian energy in region of electromagnetic spectrum ranging from wave length ,0.8 to 500nm.I.R spectrum is divided in to three regions (a)near I.R 2500 TO 4000 cm-1 (b) mid I.R 4000 TO 400cm-1 (c) far I.R 400 to 20 cm-1 ,only the mid region is referred to simply as infra red &widely used in the analysis of drugs &pharmaceuticals.
(iii)Fluorescence analysis
Fluorescence means the substance in diluted acid solution. absorb light over a specific range of wavelength &re-emission of absorbed light lasts only while the substance is receiving the exciting rays .The drug belladonna leaf &root ,aloes ,jalap show fluorescence in visible range .The UV light obtained from mercury vapour lamp produce fluorescence in many natural products .e.g cinchona gives purple blue fluorescence ,wild cherry gives mauve fluorescence.
(iv)Nuclear magnetic resonance spectroscopy (NMR):
Dr. Ghada Alhusaini