Carboxylic acids, adsorption

As Smith (300) has shown by infrared spectroscopy, carboxylic acids are adsorbed either by hydrogen bonding of the carboxyl group or by proton transfer to the surface. Carboxylate absorptions were observed in the spectra. Very likely O " or OH ions acted as proton acceptors although no OH absorption bands could be detected after carboxylic acid adsorption. The isoelectric point of pure anatase is near pH 6.6 (305). 

To explore this question, the adsorption of glycine on AlOOH was recently investigated at the interface with water [78, 97]. This study confirmed the occurrence of an inner sphere Al-O-C-0 bond that was predicted from calculations at the interface with vacuum, and from numerous experimental studies of carboxylic acid adsorption on alumina polymorphs (see Ref. [78] and references therein). It was found that inner sphere adsorption (shown in Fig. 5.14, right), with -161.6 and -113.6 kJ moF for the anionic and zwittetionic species, respectively is significantly more stable as compared to outer sphere adsorption (-20.5 kJ mol (Fig. 5.14, left)). Beyond the result itself, it is important to note that complex events can now he handled with ab initio methods because they are able to model aU types of forces in reasonable agreement with experiment. 

T artrazine, 4,5-dihydro-5 -oxo-1 -(4-sulfophenyl)-4-[(4-sulfophenyl)azo]-1// -pyrazole-3-carboxylic acid trisodium salt was discovered by Ziegler in 1884 and is used as a dye for wool and silk. It is used as a colour additive in foods, drugs and cosmetics, and is an adsorption-elution indicator for chloride estimations in biochemistry (B-76MI40404). 

It is well known that pMMA and pSty in THF follow ideal GPC behavior on many common GPC columns. However, many commercially important acrylate polymers contain a wide array of other monomers. In general, acrylic polymers composed of monomers that do not contain polar groups will yield well-behaved polymers, giving ideal GPC separations. Monomers that contain polar groups should prompt the analyst to carefully evaluate the possibility of adsorption of the analyte onto the column. The most common functionalities of concern are hydroxyl groups, amine groups, ethylene oxide units, and carboxylic acids. In many cases, such monomers can be tolerated. However, the acceptable level can vary considerably with even apparently minor changes in... 

The latter approach is used in the enantioselective determination of a Phase I metabolite of the antihistaminic drug, terfenadine. Terfenadine is metabolized to several Phase I compounds (Fig. 7-13), among which the carboxylic acid MDL 16.455 is an active metabolite for which plasma concentrations must often be determined. Although terfenadine can be separated directly on Chiralpak AD - an amy-lose-based CSP - the adsorption of the metabolite MDL 16.455 is too high to permit adequate resolution. By derivatizing the plasma sample with diazomethane, the carboxylic acid is converted selectively to the methyl ester, which can be separated in the presence of all other plasma compounds on the above-mentioned CSP Chiralpak AD [24] (Fig. 7-14). Recently, MDL 16.455 has been introduced as a new antihistaminic drug, fexofenadine. 

Reagents that provide UV adsorptive derivatives of carboxylic acids are fairly numerous. The preparation of the simple benzyl esters by reacting the carboxylic ion with alkyl halides or diazo compounds has been unsuccessful due to their having unacceptable toxicity. The... 

The influence of attaching different nucleophiles to the EDC-activaed carboxylic acid groups from the S-layer protein on the adsorption of selected test proteins was evaluated via relative flux losses (1 — Rf, given X 100 in %) of SUMs after filtration of the respective protein solution (BSA, OVA, CA, MYO). 

Ng, K.L., Pauli, B., Haddad, P.R., and Tanaka, K., Retention modeling of electrostatic and adsorption effects of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography, /. Chromatogr. A, 850, 17, 1999. 

Both organic and inorganic ligands such as Cl and dissolved organic carbon (fulvie acid and carboxylic acids) decrease metal adsorption. In the arid soils with higher pH, folic acids increase the solubility of metals such as Cu and Zn. The interaction between the transition of heavy metals and silicate surfaces was reviewed by McBride (1991). 

A potentially more sensitive and selective approach involves reaction of formic acid with a reagent to form a chromophore or fluorophore, followed by chromatographic analysis. A wide variety of alkylating and silylating reagents have been used for this purpose. Two serious drawbacks to this approach are that inorganic salts and/or water interfere with the derivatisation reaction, and these reactions are generally not specific for formic acid or other carboxylic acids. These techniques are prone to errors from adsorption losses, contamination, and decomposition of the components of interest. Enzymic techniques, in contrast, are ideal for the analysis of non-saline water samples, since they are compatible with aqueous media and involve little or no chemical or physical alterations of the sample (e.g., pH, temperature). 

Figure 6. EELS spectra of pyridine carboxylic acids adsorbed at Pt(lll). Experimental conditions (A and B) adsorption from 1 mM NA in 10 mM KF at pH 3, followed by rinsing with 2 mM HF (pH 3) (C) adsorption from 10 mM KF (pH 3), followed by rinsing with 0.1 mM KOH (pH 10) other conditions as in Figure 4. A. Adsorption at -0.2 V vs. Ag/AgCl (pH 3). Continued on next page.

The processes classified in the third group are of primary importance in elucidating the significance of electric variables in electrosorption and in the double layer structure at solid electrodes. These processes encompass interactions of ionic components of supporting electrolytes with electrode surfaces and adsorption of some organic molecules such as saturated carboxylic acids and their derivatives (except for formic acid). The species that are concerned here are weakly adsorbed on platinum and rhodium electrodes and their heat of adsorption is well below 20 kcal/mole (25). Due to the reversibility and significant mobility of such weakly adsorbed ions or molecules, the application of the i n situ methods for the surface concentration measurements is more appropriate than that of the vacuum... 

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