Determination of the purity of a drug is an important exercise in the evaluation of drugs. Apparent correct identity does not always guarantee the purity of the drug as drugs of correct identity can be adulterated in a variety of ways (see under adulteration). Purity of a drug implies that the sample should not contain any other substances other than the substances constituting the drug or the presence of other related substances should not in any way exceed the maximum permissible limit. In assessing the purity of a drug, many macroscopical, microscopial, chemical and biological tests are employed. Determinations used for purity assessment include determination of the amount of foreign organic matter, ash and acid-insoluble ash values, extractive values, optical rotation, refractive index, saponification value, iodine value and various quantitative physical constants and numerical values.
Determination of Quality
Good quality, that is the presence of maximum quantity of the active constituents, is the most important criterion expected in a crude drug. Thus the ultimate aim of evaluation of a drug sample is to determine its quality. In order to do that both physico-chemical and biological methods are employed. Chemical assays and various physico-chemical determinations (gravimetric, titrimetric, colorimetric, spectroscopic, chromatographic, etc.) are very efficient incorrectly estimating the amount of chemical constituents in a crude drug. Biological and microbiological assays are also very useful in determining the qualities of certain drugs. These methods are valuable in cases of drugs, which cannot be assayed by chemical methods. In these inethods, use is made of the ability of a drug to being about a specific response in a living organism or tissue. Of course, the response of the organism must be measurable in terms of dose and concentration of the test drug.
As apparent from the foregoing discussion a complete evaluation of a drug sample may involve almost all the methods and techniques available for identification and assessment of purity and quality. (For details of the various methods and procedures, students are referred to standard practical books and Pharmacopoeias).
Uamuzi wa usafi wa dawa ni zoezi muhimu katika tathmini ya dawa. "Utu sahihi wa kuonekana hauhakikishi usafi wa dawa, kwani dawa za kulevya za utambulisho sahihi zinaweza kupotoshwa kwa njia mbalimbali (tazama chini ya ""Upotovu.""" Usafi wa dawa ya kulevya unamaanisha kwamba sampuli haipaswi kuwa na vitu vingine isipokuwa vitu vinavyounda dawa ya kulevya au uwepo wa vitu vingine vinavyohusiana haipaswi kwa njia yoyote kupita kiwango cha juu kinachoruhusiwa. Katika kutathmini usafi wa dawa, vipimo vingi vya makroskopi, microscopy, kemikali na kibiolojia hutumiwa. Utaratibu wa kupima usafi ni pamoja na kuamua kiasi cha vitu vya kikaboni vya kigeni, thamani ya majivu na asidi-insoluble, thamani ya uchimbaji, mzunguko wa macho, index ya refractive, thamani ya saponification, thamani ya iodini na vigezo mbalimbali vya kimwili na thamani za nambari. Ubora mzuri, yaani, uwepo wa wingi wa kiwango cha juu cha viungo vya kazi, ni kipimo muhimu zaidi kinachotarajiwa katika dawa ghafi. Hivyo lengo la mwisho la tathmini ya sampuli ya dawa ni kuamua ubora wake. Ili kufanya hivyo, mbinu za kimwili na za kibiolojia hutumiwa. Vipimo vya kemikali na vipimo mbalimbali vya fizikia na kemikali (gravimetric, titrimetric, colorimetric, spectroscopic, chromatographic, nk) Ni muhimu sana kwa ajili ya kukadiria kiasi cha kemikali katika dawa. Uchunguzi wa kibiolojia na wa vijidudu pia ni muhimu sana katika kuamua sifa za dawa fulani. Mbinu hizi ni muhimu katika kesi za dawa, ambazo haziwezi kupimwa kwa njia za kemikali. Katika inethods hizi, matumizi ni kufanywa ya uwezo wa dawa ya kuwa kuhusu majibu maalum katika hai hai au tishu. Bila shaka, mwitikio wa kiumbe lazima upimwe kwa habari ya kipimo na mkusanyiko wa dawa ya mtihani. Kama inavyoonekana kutoka kwa majadiliano ya hapo juu, tathmini kamili ya sampuli ya dawa inaweza kuhusisha karibu mbinu zote na mbinu zinazopatikana kwa utambulisho na tathmini ya usafi na ubora. (Kwa maelezo ya mbinu mbalimbali na taratibu, wanafunzi ni rejea kwa vitabu vya kawaida vitendo na Pharmacopoeas).