Nonaqueous acid-base titration

Many pharmaceutical compounds are weak acids or bases that can be analyzed by an aqueous or nonaqueous acid-base titration examples include salicylic acid, phenobarbital, caffeine, and sulfanilamide. Amino acids and proteins can be analyzed in glacial acetic acid, using HCIO4 as the titrant. For example, a procedure for determining the amount of nutritionally available protein has been developed that is based on an acid-base titration of lysine residues. ... 

QuaHty control in the production of organic solvent finish removers may be done by gas—Hquid chromatography, which allows the manufacturer to determine the actual ratio of volatile solvent present in the finished product. If the product does not meet specifications, solvents can be added to bring the product to an acceptable composition. A less expensive approach is to use a hydrometer to determine the specific gravity of the product. The specific gravity indicates if the proper blend has been reached. Nonaqueous acid—base titration may be used to determine the amount of acid or alkaline activator present in a remover. 

Solvent choices for nonaqueous acid-base titrations have been reviewed by Lagowski. ... 

The study of nonaqueous titrations covers a very broad field. It can include acid-base titrations, oxidation-reduction titrations, precipitation-titrations, and titrations involving complex formation. In order to limit things somewhat, I would like to discuss only nonaqueous acid-base titrations. However, I do not mean to imply that other types of titrations carried out in nonaqueous media are of lesser importance. For example, some excellent oxidation-reduction titrations have been carried out by Dr. Stone of Michigan State and as an example of a precipitation titration, we developed a method several years ago for titrating sulfate with barium that is carried out at least partly in nonaqueous solution. Other examples could be given but to mention all of them would lead to an excessively prolonged discussion. 

There are two major areas of use for nonaqueous acid-base titrations. The first is the direct determination of compounds that have definite acidic or basic properties. This includes many thousands of organic compounds. For example, many amines are basic and can be titrated. There are also numerous acidic compounds, such as sulfonic acids, phosphonic acids, carboxylic acids, enols, imides, phenols, sulfur compounds, and others which can be titrated. The second largest and most important use of nonaqueous acid-base titrations is the indirect deter-... 

What are some of the advantages of nonaqueous acid-base titrations First of all, they are cheap. Secondly, they are simple in many cases you don t need a trained chemist to do them. A third advantage is that nonaqueous acid-base titrations are extremely accurate. For the analysis of organic compounds where you are assaying a major constituent, nonaqueous acid-base titrations are unmatched in their accuracy. I think it is well to reme-ber that some of the very excellent instrumental methods are, in many cases somewhat inaccurate. Finally, why use some smelly solvent such as acetic acid or pyridine, as is frequently necessary, instead of water or perhaps water mixed with alcohol The reason for this is that nonaqueous titrations are much broader in their application than are acid-base titrations carried out in water or in water mixtures with a waterlike solvent such as alcohol. 

The objective of this brief discussion on titrations is to relate the parameters discussed in other chapters to the problem associated with this technique. In other words, an aqueous or nonaqueous acid-base titration is nothing more than a series of pH measurements. All of the precautions, techniques, and equipment previ-... 

Fritz, J. S. Acid-Base Titrations in Nonaqueous Solvents. Allyn and Bacon Boston, 1973. 

Potcntiomctric Titrations In Chapter 9 we noted that one method for determining the equivalence point of an acid-base titration is to follow the change in pH with a pH electrode. The potentiometric determination of equivalence points is feasible for acid-base, complexation, redox, and precipitation titrations, as well as for titrations in aqueous and nonaqueous solvents. Acid-base, complexation, and precipitation potentiometric titrations are usually monitored with an ion-selective electrode that is selective for the analyte, although an electrode that is selective for the titrant or a reaction product also can be used. A redox electrode, such as a Pt wire, and a reference electrode are used for potentiometric redox titrations. More details about potentiometric titrations are found in Chapter 9. 

Fritz, J.S., Acid-Base Titration in Nonaqueous Solvents Allyn and Bacon Boston, 1973 Chapter 2. 

B. Chemical Reactions in Solvents and Melts, Pergamon Press, Oxford, 1969 Gyenes, 1. Titrationen in Nichtwdsserigen Medien, F. Enke, Stuttgart, 1970 Fritz, J.S. Acid-Base Titrations in Nonaqueous Media, Allyn Bacon, Needham Heights, MA, 1973 Kratochvil, B. 

J. S. Fritz, Acid-Base Titrations in Nonaqueous Solvents (Boston Allyn Bacon, 1973) J. Kucharsky and L. Safarik, Titrations in Non-Aqueous Solvents (New York Elsevier, 1963) W. Huber, Titrations in Nonaqueous Solvents (New York Academic Press, 1967) I. Gyenes, Titration in Non-Aqueous Media (Princeton, NJ Van Nostrand, 1967). 

Water is highly unusual in the extent of its interactions with solutes, but even minimal solvent-solute interactions can play a major role in the nature of chemical reactions. To calculate pH during acid-base titrations in a nonaqueous solvent, we must consider not only the equilibria discussed in Chapter 3 but also reactions discussed in Sections 4-2, 4-3, and 4-4. 

The purpose of this chapter is to consider the preparation and standardization of acids and bases and to review some of the important applications of acid-base titrations in aqueous and nonaqueous systems. For end points to be detected most precisely, the pH in the vicinity of the equivalence point should change sharply. For this reason a solution of strong acid or base is chosen as titrant whenever possible. 

J. s. fritz Acid-Base Titrations in Nonaqueous Solvents, G. F. Smith Chemical, Columbus, Ohio, 1952 Acid-Base Titrations in Nonaqueous Solvents, Allyn and Bacon, Boston, 1973. 

Titration The determination of assay values for reference standards, counter-ions, or impurities can often be independently determined via titration. While titration assays generally have less selectivity in comparison to chromatographic methods, the advantages of a broad spectrum of classical titration techniques that exist for organic functional groups is often overlooked. The methodologies include not only classical potentiometric acid/base titrations but also nonaqueous, redox, indirect, precipitation, and derivatization titrations.76-79... 

Acid-Base Titrations in Nonaqueous Solvents. It is a fact that the apparent acidity or basicity of a compound is strongly dependent on the acid-base properties of the solvent. For example, very strong acids such as HCl and HNO3 cannot be individually titrated in water because water is sufficiently basic that these acids appear to be totally ionized. Very weak bases, such as amines, cannot be successfully titrated with strong acid in water. Many acids or bases that are too weak for titration in an aqueous medium, however, become amenable to titration in appropriate nonaqueous solvents. As a consequence, there are now many neutralization methods that call for solvents other than water [23-25]. 

J. Fritz, "Acid-Base Titrations in Nonaqueous Solvents", The G. Frederick Smith Chemical Comnany,... 

Use of potentiometry for pH titration allows analyses to be carried out in colored or turbid solutions. Also, it solves the problem of selecting the correct indicator for a particular acid-base titration. The endpoint can be determined more accurately by using a first or second differential curve as described earlier. It also permits pH titrations in nonaqueous solvents for the determination of organic acids and bases as described subsequently. In addition, it can be readily automated for unattended operation. 

An acid-base titration is a quick and convenient method for the quantitative analysis of substances with acidic or basic properties. Many inorganic and organic acids and bases can be titrated in aqueous media, but others, mainly organic, are insoluble in water. Fortunately, most of them are soluble in organic solvents hence they are conveniently determined by nonaqueous acid-base titrimetry. Although acid-base titrations can usually be followed potentio-metrically, visual endpoint detection is quicker and can be very precise and accurate if the appropriate indicator is chosen. 

Table 1 Examples of acid-base titrations in nonaqueous solvents ...

Reactions at the Silicon Nitride - Solution Interface - A study was conducted to determine the extent of aqueous reactions at the silicon nitride-water interface. It was demonstrated that up to 27 days are required to stabilize reactions at the interface as indicated by Ph and particle electrophoresis measurements. A semiautomatic titrator was also purchased and set up to utilize acid-base titrations to study the silicon nitride-solvent interface. A particular emphasis of this work will be on the nonaqueous potentiometric and conductometric titration to determine the strength of acid and base sites on the silicon nitride surface. 

Controlled-current coulometry (coulometric titration) can be utilized to determine not-easily oxidizable (or reducible) analytes of different applications via acid-base, precipitation, com-plexation titrations, etc. Furthermore, it benefits short analysis time and small amount determination [2]. Dzudovic et al. [21] reviewed some studies employing acid-base titrations for the determinations of non-aqueous or water-insoluble compounds (organic and inorganic). Typically, acidimetric titrations were undertaken coulometrically based on the EF liberated by the oxidation of the introduced H2O. Coulometric titrations of bases in nonaqueous solvent were performed using anodic depolarizers (titrants) to generate as a source. On the other hand, coulometrically atkalimetric... 

When the functionalized polymer contains acidic or basic groups, such as those in ion-exchange resins, the acid-base titration methods are the most suitable for functional group determination. Such methods are well-established (Helfferich, 1962), In one report (Schou et aL, 1975), the free amino group in an unblocked resin-peptide was determined by nonaque-ous titration with acid. Similarly, histidine incorporation could be deter-... 

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