Functional group titrations

A plot of pAia as a function of a can thus be regarded as a measure of the ease of proton removal from the polyion at a given degree of ionisation. The shape of the pAia versus a plot depended on the polymer being titrated. However, the polymers exhibited buffering capacity at higher pH values than commonly found 

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A suitable functional group is assayed in the same sample. In general chemistry and many polymer applications, this is merely the titration of acid groups with a base, or vice versa. Note that only volumetric glassware and a method for end point determination are required to do this. 

In this case there is one functional group of each kind per molecule, and each could titrated as a double check of the method. 

Functional Group Analysis. The total hydroxyl content of lignin is determined by acetylation with an acetic anhydride—pyridine reagent followed by saponification of the acetate, and followed by titration of the resulting acetic acid with a standard 0.05 W sodium hydroxide solution. Either the Kuhn-Roth (35) or the modified Bethge-Liadstrom (36) procedure may be used to determine the total hydroxyl content. The aUphatic hydroxyl content is determined by the difference between the total and phenoHc hydroxyl contents. 

The other analytical methods necessary to control the typical specification given in Table 5 are, for the most part, common quality-control procedures. When a chemical analysis for purity is desired, acetylation or phthalation procedures are commonly employed. In these cases, the alcohol reacts with a measured volume of either acetic or phthalic anhydride in pyridine solution. The loss in titratable acidity in the anhydride solution is a direct measure of the hydroxyl groups reacting in the sample. These procedures are generally free from interference by other functional groups, but both are affected adversely by the presence of excessive water, as this depletes the anhydride reagent strength to a level below that necessary to ensure complete reaction with the alcohol. Both procedures can be adapted to a semimicro- or even microscale deterrnination. 

It was noted that the content of functional groups on the surface of studied A1,03 was 0,92-10 mol/g of acid character for (I), FOS-IO mol/g of basic character for (II). The total content of the groups of both types was 1,70-lO mol/g for (III). The absence of appreciable point deviations from a flat area of titration curves in all cases proves simultaneously charges neutralization character on the same adsoi ption centers and non-depending on their density. The isoelectric points of oxide surfaces have been detenuined from titration curves and have been confirmed by drift method. 

This expression has the same form as Eqs. (6-81) and (6-84). Here, of course, the substrate is not protonated to an appreciable extent. With other suitable experiments and some luck, the steady-state situation can be distinguished from substrate titration. For example, is the pKa value deduced under the assumption of a titration reasonable for the molecule in question That is, is it reasonable for one of the functional groups of A to have a pKa near the pH of the bend Can one detect significant amounts of two species, AH+ and A, at a pH near the presumed pKal Can one modify the substrate, eliminating the site of protonation If so, and if a titration mechanism operates, then (as the reader should show) the pH profile should become linear. Obviously, were substrate titration and a steady-state intermediate situation to coexist in the same system, a more complicated but not intractable situation would result. 

The fact that in HPLC only UV-active components are registered, whereas in titration all basic functional groups are detected constitutes a difference in specificity (quality) and sensitivity (quantity) of these two methods relative to a given impurity. See Fig. 4.17 (left). [Solvent A (water) behaves differently from the other four as can be seen from Fig. 4.17 (right). The material was known to exist in a crystal modification that theoretically contains 3.2% water, and moderate drying will most likely drive off only the excess Indeed, the best-dried batches are all close to the theoretical point (circle, arrow in Figs. 4.16-17), and not near zero. This is only partly reflected in Table 4.15, column A for this reason tabular and graphic information has to be combined. Solvent B, which is an alcohol, behaves more like water... 

The potentiometric titration was carried out in order to determine the functional groups present in the biomass surface. During the titration experiments, the C02-free condition was always maintained to avoid the influence of inorganic carbon on the solution pH. Detailed potentiometric titration procedure and estimation method of functional groups are available in the previous reports [4,6]. 

Bacterial cell walls contain different types of negatively charged (proton-active) functional groups, such as carboxyl, hydroxyl and phosphoryl that can adsorb metal cations, and retain them by mineral nucleation. Reversed titration studies on live, inactive Shewanella putrefaciens indicate that the pH-buffering properties of these bacteria arise from the equilibrium ionization of three discrete populations of carboxyl (pKa = 5.16 0.04), phosphoryl (oKa = 7.22 0.15), and amine (/ Ka = 10.04 0.67) groups (Haas et al. 2001). These functional groups control the sorption and binding of toxic metals on bacterial cell surfaces. 

In the titration curves shown in Fig. 23-5, you start with the fully protonated form of the amino acid. Notice that at pH s that are not near the pKa of any functional group, the pH changes more when base is added. Also notice that there are multiple buffer regions (where the pH doesn t change rapidly when base is added) when there are multiple acid and base groups present. If the pAVs of two groups are close to each... 

In titrating a suspension of a-FeOOH (6 g e- 120 m2 g-1 2 10 4 mol g-1 surface functional groups (=FeOHTOT)) in an inert electrolyte (10 1 M NaCICU) with NaOH or HCI (Cb and Ca= concentration of base and acid, respectively, added per liter), we can write for any point on the titration curve... 

Suitable characterization techniques for surface functional groups are temperature-programmed desorption (TPD), acid/base titration [29], infrared spectroscopy, or X-ray photoemission spectroscopy, whereas structural properties are typically monitored by nitrogen physisorption, electron microscopy, or Raman spectroscopy. The application of these methods in the field of nanocarbon research is reviewed elsewhere [5,32]. 

No carboxylic acid functionality was detected either by thin-layer chromatographic analyses or by end-group titration. Therefore, procedures are now available to control the carbonation of polymeric organolithium compounds to efficiently produce either the carbox-ylated chain ends or the corresponding ketone dimer. 

The potentiometric titration curves of gels, which relate the pH of the exterior solution to the degree of ionization of the gel, resemble the titration curves of monofunctional acids or bases. However, the dissociation constants differ, often by two orders of magnitude, from the expected value for the functional group, and the slope of the curves is not the usual one. Addition of neutral salt changes the picture markedly and brings the curves closer to expectation. In the case of weak or medium... 

Other destructive methods that are widely used for qualitative analysis, on account of their simplicity and speed, are color tests specific for particular functional groups. These have been developed mainly for the detection of amines in SPPS. Titrations and derivatizations can also be performed, but are often inaccurate, time-consuming and of limited use. A review of all these methods has been published recently by Kay et al. [148] More recently, new color tests for alcohol [149, 150], thiol [151] and aldehyde [152, 153] functionalities have also been reported. 

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