Aqueous titrations

Aqueous titration with IN sodium hydroxide is the usual malic acid assay. Maleic and fumaric acid are deterrnined by a polarographic method. Analytical methods have been described (40). 

Analytical and Test Methods. Aqueous titration with 1 AiNaOH remains the official method for assaying citric acid (39,40). Although not citrate-specific, the procedure is satisfactory in the absence of interfering substances. Low concentrations of citric acid can be deterrnined by a... 

Determinations in non-aqueous solvents are of importance for substances which may give poor end points in normal aqueous titrations and for substances which are not soluble in water. They are also of particular value for determining the proportions of individual components in mixtures of either acids or of bases. These differential titrations are carried out in solvents which do not exert a levelling effect. 

Non-aqueous titrations have been used to quantify mixtures of primary, secondary and tertiary amines,5 for studying sulphonamides, mixtures of purines and for many other organic amino compounds and salts of organic acids. 

The various relationships concerning the interconversion between un-ionised and ionised or different resonant forms of indicators referred to in Section 10.7 apply equally well to those indicators used for non-aqueous titrations. However, in this type of titration the colour change exhibited by an indicator at the end point is not always the same for different titrations as it depends upon the nature of the titrand to which it has been added. The colour corresponding to the correct end point may be established by carrying out a potentiometric titration while simultaneously observing the colour change of the indicator. The appropriate colour corresponds to the inflexion point of the titration curve (see Section 15.18). 

The majority of non-aqueous titrations are carried out using a fairly limited... 

As indicated in Section 2.4 the strength of an acid (and of a base) is dependent upon the solvent in which it has been dissolved, and in Sections 10.19-10.21 it has been shown how this modification of strength can be used to carry out titrations in non-aqueous solvents which are impossible to perform in aqueous solution. Potentiometric methods can be used to determine the end point of such non-aqueous titrations, which are mainly of the acid-base type and offer very valuable methods for the determination of many organic compounds. 

Table 15.6 Some common potentiometric non-aqueous titrations...

Potentiometric titrations - continued EDTA titrations, 586 neutralisation reactions, 578, 580 non-aqueous titrations, 589, (T) 590 oxidation-reduction reactions, 579, 581, 584 precipitation reactions, 579, 582 Potentiometry 548 direct, 548, 567 fluoride, D. of, 570 Potentiostats 510, 607 Precipitants organic, 437 Precipitate ageing of, 423 digestion of, 423... 

After the acetylation, the analytical finish is not based on non-aqueous titration, but consists in acid titration after complete conversion of the anhydride with water and by comparison with a blank determination. 

Whereas in many instances potentiometric non-aqueous titrations of acids can show anomalies24 depending on the type of solvents and/or electrodes (owing to preferential adsorption of ions, ion pairs or complexes on the highly polar surface of the indicator electrode, or even adherence of precipitates on the latter), conductometric non-aqueous titrations, in contrast, although often accompanied by precipitate formation30, are not hindered by such phenomena sometimes, just as in aqueous titrations, the conductometric end-point can even be based on precipitate formation34. 

According to Harlow73, it is nevertheless one of the least unstable quaternary ammonium hydroxides (see under practice of non-aqueous titration, p. 281). 

Neutralization with KOH in aqueous THF gave the desired poly(styrene-b-potassium methacrylate) (S-b-MA.K). The carbonyl band in the IR spectrum is replaced with a strong, broad carboxylate absorption centered near 1566 cm 1 (Figure 2c). The carboxylate and potassium contents were assayed by non-aqueous titration and ICP, respectively. The resulting values of 0.91 meq COj /g and 0.98 meq K/g indicate essentially quantitative conversion to the potassium methacrylate. S-b-MA.K obtained in this manner is easily dissolved in solvents such as THF and dichloromethane, in contrast to the... 

Nickel and Weber [30] reported aqueous titrations of carboxylic acids, phenols, acidic drugs containing NH groups, cationic acids (ammonium salts) in dimethyl-formamide solution against 0.1 M potassium hydroxide aqueous solution as the... 

Rizk et al. [3] used 2,3-dichloro-5,6-dcyano-/)-benzoquinone as a redox titrant in the aqueous titration of penicillamine. Finely ground tablets were mixed with H20 and the mixture was filtered. The filtrate (or an injectable solution) was diluted with H20 and acidified with H3PO4 before titration with the redox titrant. The titration was conducted in anhydrous acetic acid using thiethylperazine dihydrochloride as the indicator. The endpoint was detected by a color change to green, and recoveries of penicillamine were 98.4-100.5%. 

A non-aqueous titration method was developed (25,26) for the determination of basic compounds with thio(-S-) and mercapto (-SH-) groups. The reaction of the S group with Hg (0Ac)2 in acetic acid makes this possible. Methimazole and other compounds were all titrated with HCIO in acetic acid using gentian violet as indicator. 

Non-aqueous titration of tablet extracts with sodium methoxide(27) or lithium methoxide(l)(2) has been reported. 

The determination of neomycin by non-aqueous titration has been described by Penau et all2l. Neomycin base is allowed to react with standardised perchloric acid the excess acid is then back-titrated with potassium hydrogen phtha-late using crystal violet as indicator. To determine the neomycin content of the sulphate salt the same authors precipitated the sulphate with benzidine before reacting the neomycin with perchloric acid. The amount of benzidine required to precipitate the sulphate is calculated from the sulphate content which is itself determined by titration with sodium hydroxide. 

What do you understand by direct titration method in the context of Aqueous Titrations Discuss in details the procedure involved in the assay of ... 

Residual titration method is an alternative means of assay of drugs by Aqueous Titrations . Justify the statement with the help of assay of the following pharmaceutical substances ... 

In order to overcome these shortcomings the non-aqueous titrations were introduced. 

Non-aqueous titrations have the following advantages, namely ... 

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