Determination of carboxyl groups

Springer Series in Wood Science Methods in Lignin Chemistry (Edited by S.Y. Lin and C.W. Dence) 

The procedure described below was developed by Pobiner (1983) and consists of the nonaqueous potentiometric titration of lignin with tetra-n-butylammonium hydroxide in the presence of an internal standard, p-hydroxybenzoic acid. As is true also for conductometric titrations of lignin (see Chap. 7.7), phenolic hydroxyl and sulfonic acid groups may be coincidentally determined by this procedure. 

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Bobka (144) studied the adsorption of diphenylguanidine on graphite wear dust. As was shown by Rivin (85), diphenylguanidine adsorption is equivalent to NaHCOj neutralization in the determination of carboxyl groups. With increasing grinding time, surface area and diphenylguanidine adsorption increased parallel to each other. 

Determination of Carboxylic Group Terminals. The carboxylic group terminals were determined by alkali titration (12.). After 200 mg of the sample was dissolved in T.5 ml of benzyl alcohol in a nitrogen atmosphere at 110 °C, the solution was titrated with 0.05N potasL- Vum hydroxide using phenolphthalein as an indicator. A blank test was carried out by the same method but omitting the sample. 

Table 2 Classical methods for determination of carboxyl groups in cellulose...

With selective labels available, visualization of oxidative damage in all spatial dimensions of paper materials will become a major issue, especially with regard to conservation issues and restoration of historical paper documents. For the determination of carboxyl groups improvements in the reliable quantification of lactones can be considered a future challenge. 

Determination of Carboxyl Groups by Nonaqueous Potentiometric Titration... 

The standard deviation in a series of replicate determinations of carboxyl group concentrations at the 1.05 mEq g 1 level in a lignosulfonate was found to be 0.060 mEq g 1 for a lignosulfonate having a carboxyl content at the 2.99mEqg level, the standard deviation was 0.043 mEqg-1 (Pobiner 1983). 

The affinity of variously oxidized cellulosic materials for certain basic dyes, notably methylene blue, has long been known. Kenyon and coworkers have recently shown that in the case of nitrogen dioxide oxycelluloses, the methylene blue absorption is a function of the carboxyl group content. Application of the reversible methylene blue method to the determination of carboxyl groups in purified cellulose has been made by Davidson and by Weber, who was able to show good agreement with the cation-exchange methods previously considered as well as with viscosity and osmotic pressure measurements. 

Holtzclaw, K. M. and Sposito, G. (1979). Analytical properties of the soluble, metal-complex-ing fractions in sludge-soil mixtures IV. Determination of carboxyl groups in fulvic acid. Soil Sci. Soc. Am. J. 43, 318-323. 

O. Ant-Wuorinen, Determination of Carboxyl Groups in Cellulose Report 96, The State Institute for Technical Research, p. 48, Helsinki, Finland (1951). 

Micro-amounts of carboxyl groups in individual compounds are determined by pyrolytic decarboxylation of organic acids via pyrolysis in a helium atmosphere in the presence of copper carbonate and quinoline accompanied by liberation of an equivalent amount of carbon dioxide [143]. The determination of carboxylic groups by heating the sample to 385°C without reagents has been described [144]. Whyte and Engler... 

De Nobih M., Contm M. (1994), Determination of carboxyl groups content in fulvic acids by the CTA (Cetyltrimethylammonium) method, Humic Substances in the Global Environment and ImpUcarions on Human Health, (Ed. N. Sene.si, T.M. Miano), Elsevier Science, 263-268. 

As bases sodium bicarbonate, NaHCOs (pKa=6.37), sodium carbonate, Na2C03 (pKa.=10.25), sodium hydroxide, NaOH (pKa= 15.74) and sodium ethoxide, NaOCzHs (pKa=20.58) are used. It is assumed that sodium bicarbonate neutralizes carboxylic acids, sodium carbonate - carboxylic acids and lactones, sodium hydroxide - carboxylic acids, lactones and phenols, whereas sodium ethoxide will react with all oxygen species, even extremely weak acids (pKa< 20.58). fti practice Boehm titration is limited to the determination of carboxylic groups, lactones and phenols [192 197]. Sodium ethoxide is not used very often owing to the necessity of performing the experiment in nonaqueous media and oxygen-free conditions. One of the reasons why the sodium salts were chosen as bases is that they do not form precipitates after reaction with gaseous CO2 and their specific interactions with carbon surfaces are minimal [198]. 

Heacock [24] has described a method for the determination of carboxyl groups in oxidised polyolefins without interference by carbonyl groups. This procedure is based upon the relative reactivities of the various carbonyl groups present in oxidised PE film to sulfur tetrafluoride gas. The quantity of the carboxyl groups in the film is then measured as a function of the absorption at 5.45 pm. 

Most methods for the determination of carboxyl groups in polymers are based on titration techniques including, for example, the following copolymers acrylic acid-itaconic acid [16], acrylic acid-ethyl acrylate [17] and maleic acid-styrene [18]. High-frequency titration has been applied [19] to the analysis of itaconic acid-styrene and maleic acid-styrene copolymers. The method can also be used to detect traces of acidic impurities in polymers, and in the identification of mixtures of similar acidic copolymers. Titration indicates that the acid segments in the copolymers of itaconic acid-styrene, and maleic acid-styrene, and the homopolymer polyitaconic acid, act as dibasic acids. The method has a sensitivity that permits identification and approximate resolution of two carboxylate species in the same polymer, for example ... 

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