METHODS OF DRUG ANALUSIS

.FUNCTIONAL GROUP METHODS
.PHYSICOCHEMICAL METHODS

Chemical compounds are usually analyzed through reactions that are specific for an ion, radical, or functional group. In inorganic analysis by volumetric means it has become common to classify these reactions according to the type of reaction occurring during the titration procedure. For example, such terms as acidimetry, alkalimetry, precipitation, or oxidation-reduction are commonly employed to classify such titrations. In organic analysis such a classification is less meaningful. In such analyses it is more useful to consider the functional group involved in the reaction. Since most analytical reactions are not specific for a single compound but may be employed in analyzing any compound containing a like ion, radical, or functional group, this lack of specificity permits a broad means of classifying analytical methods. It further permits a classification that may be employed to select methods of analysis for new or previously unanalyzed compounds.
While such classification is of great value to students of pharmaceutical analysis, it must be understood that no single determination can always be used for the analysis of a specific functional group, ion, or radical. The presence of other groups, either in the compound being analyzed or in other compounds present in a pharmaceutical preparation, may interfere with, or prevent, the reaction from being quantitative. For this reason a number of analytical reactions have been developed for each functional group. In addition to knowing the various reactions applicable to each functional group, the analyst must understand thoroughly their limitations so as to select that reaction most suitable for the mixture or compound being analyzed.
For example, an analyst must not only recognize that phenols may be determined by measuring the quantity of bromine employed to convert the phenol to 2,4,6-tribromophenol but must also realize that this reaction will be worthless to analyze phenol dissolved in a vegetable oil. Such an oil, because of its unsaturation, will also react with bromine and interfere with its determination. The analyst therefore must be familiar with the analytical reactions and methods available for quantitative determinations and must be able to select the best reaction and utilize it in the proper analytical procedure for the compound being analyzed. He cannot rely solely upon standard procedures but must be able to modify these to develop suitable assays for new compounds and new pharmaceutical mixtures.

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