Potentiometric titration, neutralization precipitation

Codeine is a strong mono-acid base and its solutions turn litmus blue, phenolphthalein pink, and helianthin yellow [65] it is incompletely precipitated from its salts by ammonia. The neutral point of a codeine-hydrochloric acid titration is at pH 4-93, so methyl red can be used as indicator [66-67] potentiometric titrations can also be used [68-72],... 

The potentiometric titration curve of ferric enterobactin, shown in Figure 3, has a sharp inflection after the addition of six equivalents of base. Such a break indicates that the six phenolic oxygens from the three dihydroxybenzoyl groups are displaced by ferric ion in the ferric enterobactin complex. This interpretation is further supported by the absorbance maximum at 490 nm (e 5600), which is very similar to simple tris(catecho-lato)iron(III) complexes (, T). The very low pH at which com-plexatlon of enterobactin occurs, with virtually complete complex formation by pH 6, is a strong indication of a very stable complex. However, the titration is prematurely terminated at pH 3.8 by the precipitation of a purple neutral iron complex (whose composition and structure will be discussed later) which makes it impossible to determine the stability consteint of ferric enterobactin from potentiometric data alone. 

Manual potentiometric pKa pKk Simple, rapid Not for low or overlapping pKaS precipitation when titrated to neutral species multiple experiments required >0.0025 M (2.5 mM) 50 mg... 

Among them, volumetric methods are presumably the most widely used for water analysis. They are titrimetric techniques which involve a chemical reaction between a precise concentration of a reagent or titrant and an accurately known volume of sample. The most common types of reactions as used within this method are acid-base neutralization, oxidation-reduction, precipitation, and complexation. The use of an indicator which identifies the equivalence point is required to develop this kind of method. The modem laboratories usually employ automated endpoint titrators, which largely improve the efficiency and reliability of the determination. Moreover, spectrophotometric, potentiometric, or amperometric methods to determine the endpoint of the reaction can... 

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