Acidimetric methods

Szakacs-Pinter and Perl-Molnar described a new and simple procedure for the determination of choline and its derivative. The method is based on the acidimetric determination of the volatile base produced by the K2S2O8 oxidation of choline in an alkaline medium [12], The procedure 

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This acidimetric method was developed by Dr. W. I. Patnode for use with methylchlorosilanes and has since been adapted to many other halosilanes. A similar method was used by Hyde and DeLong, J. Am. Chem. Soc. 63, 1194 (1941). 

Alkalimetric and acidimetric methods are not to be used because of interference from acids or bases in some carbons. The effect is illustrated by an experience with a test that involved the adsorption of aniline. As first conducted, the residual unadsorbed aniline was measured by a specific chemical test. The method was tedious, however, and it was thought the procedure could be shortened and simplified by titrating the unadsorbed aniline with an acid. But the residual aniline thus measured often differed from that measured by the specific chemical test. The deviations were traced to the presence of free acid on some carbons and free alkali on others. Carbons with a high pH gave a false high residual aniline, whereas carbons of low pH showed a false low residual concentration of aniline. Similar experiences are reported in the use of acidimetry and alkalimetry to measure the adsorption of other substances. 

An important survey on the above methods is available [1]. The acidimetric method is not specific to phosgene and is based on reaction according to the following equation ... 

Various methods can be used to analy2e succinic acid and succinic anhydride, depending on the characteristics of the material. Methods generally used to control specifications of pure products include acidimetric titration for total acidity or purity comparison with Pt—Co standard calibrated solutions for color oxidation with potassium permanganate for unsaturated compounds subtracting from the total acidity the anhydride content measured by titration with morpholine for content of free acid in the anhydride atomic absorption or plasma spectroscopy for metals titration with AgNO or BaCl2 for chlorides and sulfates, respectively and comparison of the color of the sulfide solution of the metals with that of a solution with a known Pb content for heavy metals. 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

Ghlorophenol Analysis. The chlorophenols can be analy2ed by acidimetric titration of the hydroxyl function (50). This overall method yields only an approximate evaluation for mixtures. To analy2e chlorophenol mixtures, gas chromatography has been the reference method used, as it made it possible to separate and quantify the various chlorophenols (51), but this technique can be a source of errors the gem-chlotinated cyclohexadienones that may be present along with the chlorophenols are broken back down iato lighter chlorophenols under the analysis conditions usually employed. 

A limited number of pure substances are available from NIST, primarily clini-cally-relevant compounds such as cholesterol, urea, uric acid, creatinine, glucose, cortisol, tripalmitin, and bilirubin (NIST SRM website). These compounds are certified for purity (greater than 99 %) and are used as primary calibrants in definitive methods for these clinical analytes (see below). Several additional pure substances are available for specific applications such as microchemistry, i.e. elemental composition (acetanilide, anisic acid, cystine nicotinic acid, o-bromobenzoic acid, p-fluoro-benzoic acid, m-chlorobenzoic acid), polarimetric standards (sucrose and dextrose), acidimetric standard (benzoic acid and boric acid). Only three pure substance NIST RMs are available for environmental contaminants, namely the chlorinated pesticides, lindane, 4,4 -DDT, and 4,4 -DDE. 

While the role of acid-base indicators in acidimetric titrations has been surpassed by more advanced, automatic, potentiometric methods various metallochromic indicators are still in use in complexometric analysis. Here we shall deal only with acid-base indicators. 

Neutralization reactions between Lowry-Bronsted acids and bases are frequently employed in chemical analysis. Methods based on them are sometimes termed acidimetric or alkalimetric. 

A few typical examples of acidimetric titrations, employing direct titration method (DTM) and residual titration method (RTM) from the Pharmacopoeia of India are described here ... 

In this method the sample is reacted with a measured excess of aq KOH, using isopro-panol as a mutual solvent, if required (but not for EtAcet). The amt of KOH consumed, which is detd by titrating tbe excess with std mineral acid, is a measure of the ester originally present. Since this detn is based on acidimetric... 

In addition to these methods, there may be mentioned that of testing the value of vitriol by an acidimetrical process, with a standard solution of alkali. 

Alkali metal complexes may be analyzed for their metal content by simple acidimetric titration. Analysis for adduct (hydroxide) content is more involved, and entails the assumption that there can be no water of hydration attached to an alcoholate anion. The method involves first, dissolving the complex in anhydrous methanol, and then, treating the resulting solution with an appropriate anhydrous add, such as tartaric acid. The acid serves to convert any hydroxide ion into water (reaction S),... 

The determination of partition caefcients by the potentiometric method is part of the function of the Sirus PCA101 (Avdeef, 1993). Typically, a preacidiLed solution of a weak acid is alkalimetrically titrated to some appropriately high pH the partition solvent such as octanol is then added, and the dual-solvent mixture is acidimetrically titrated back to the starting pH. Analysis of the two titration curves will yield two fKgS pl< and pol, where pdQ, is the apparent constant derived from... 

Unfortunately, the dependence of the rates on pH cannot be measured by our method since acidimetric titrations are not possible in buffered solutions. However, in weakly acidic and neutral solutions, there cannot be much influence because otherwise no rate constants could have been obtained. In alkaline solution, on the other hand, a base induced fragmentation occurs, which is faster by some powers of 10 than the solvent fragmentation. Thus, in 0.025N methanolic NaOH at 0°C, the half lifetime of stilbene ozonide is only 2 minutes. 

The surface protonation equilibria are interpreted according to the constant-capacitance model of Schindler and Stumm (1987). The two model parameters, the intrinsic constant pK x (intr.) at zero surface charge and the integral capacitance of the flat electric double layer C( = 2 Fm"2) are determined from titration curves. The methods of the acidimetric titration of kaolinite suspensions are discribed by Wieland (1988). 

Acidimetric titrations were performed according to the Tanabe method (with N-butylamine) [8],... 

Figure 9. Exemplification of the method used in deriving the fixed charge of an oxide in absence of specifically adsorbable ions, surface acidity constants, and surface potential from alkalimetric-acidimetric titration curves.

The method preferred in practice for determining the content of "free carbon dioxide", hydrogen carbonate ions and carbonate ipns, and thereby the total carbon dioxide content, is to titrate the water sample acidi-metrically. Carbonic acid is a dibasic acid it dissociates in two stages. The interrelationship which forms the basis of the acidimetric titration... 

The nitrogen contained in organic substances in water is converted to ammonium ions by KjeldahEs decomposition method. The ammonium ions are distilled from alkaline solution as ammonia, collected in boric acid solution and determined acidimetrically or photometrically in the receiver. Ammonium ions originally contained in the sample are separated, identified and deducted, or separated off by distillation before carrying out the Kjeldahl decomposition. Nitrite and nitrate are volatilized by H2SO4 in the... 

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