(3)Volumetric Methods of Drug Analysis

allelipraise's version from 2018-06-06 12:07

Section 1

Question Answer
Volumetric Analysis the determination of the volume of a solution of known concentration required to react with a given amount of substance to be analysed
Analytethe chemical substance being analysed; usu., the active constituent
Titrant the solution whose concentration is known; usu., added using a buret
Titration the act of adding and measuring the volume of titrant used in the assay
Indicatorusually a chemical that changes color at or very near the point in the titration where equivalent quantities of analyte and titrant have reacted
Stoichiometric (equivalence) pointthe theoretical point at which equivalent amounts of analyte and titrant have reacted
End pointthe point at which there occurs a sudden change in some property of the reaction mixture; made apparent by use of indicators or electrometrically

Section 2

Question Answer
Gram-equivalent weight (GEW)the weight in grams which is chemically equivalent to 1 gram- atom hydrogen (1.0079 g)
Gram-milliequivalent weight (GmEW)GEW/1000
Equivalent (equiv)the number of gram-equivalents involved in quantitative procedure
Milliequivelent (mEq) the number of gram-milliequivalents involved in quantitative procedure
Normality (N)the number of equivalents of solute per liter of solution or the number (equiv/L) of milliequivalents of solute per milliliter of solution (mEq/mL)
Molarity (M) an expression of the concentration of solution in terms of moles per liter

Section 3

Question Answer
Standardizationthe determination of the normality or molarity of a solution
Primary Standard a substance of known purity
Secondary Standard a standard solution whose normality or molarity was previously determined
Titerthe weight of a substance chemically equivalent to 1 mL of a standard solution

Section 4

Question Answer
Direct Assaytreatment of a soluble substance, contained in solution in a suitable vessel (analyte), with an appropriate standardized solution (titrant), the endpoint being determined instrumentally or visually with the aid of a suitable indicator.
Indirect Assay(Assay with Preliminary Treatment)
Residual Assay (“Back Titration”)requires the addition of a measured volume of a volumetric solution, in excess of the amount actually needed to react with the substance being assayed, the excess of this solution then being titrated with a second volumetric solution
Residual Assay (“Back Titration”)insoluble in inert solvents or slow reaction (the end point deviates appreciably from the stoichiometric point)
Blank Determinationconducted with the use of the same quantities of the same reagents treated in the same manner as the solution or mixture containing the portion of the substance under assay or test, but with the substance itself omitted