Anions methods compared

CE has been used for the analysis of anionic surfactants [946,947] and can be considered as complementary to HPLC for the analysis of cationic surfactants with advantages of minimal solvent consumption, higher efficiency, easy cleaning and inexpensive replacement of columns and the ability of fast method development by changing the electrolyte composition. Also the separation of polystyrene sulfonates with polymeric additives by CE has been reported [948]. Moreover, CE has also been used for the analysis of polymeric water treatment additives, such as acrylic acid copolymer flocculants, phosphonates, low-MW acids and inorganic anions. The technique provides for analyst time-savings and has lower detection limits and improved quantification for determination of anionic polymers, compared to HPLC. 

The contributions of the individual ions constituting the electrolyte have been separated following a method by Schott et al. (32). The values thus calculated indicate that the salting effects observed on the nonionic surfactants are mainly due to the prominent influence of the anions as compared to those of the cations (Holtzscherer, C. Candau, F. J. Colloid Interface Sci., in press). 

The pre-separation methods, precipitation of titan hydroxide, anion-exchange separating and scavenging with lead fluoride, were examined and the higher sensitivity of these methods compared with non-destructive determinations were observed ) for the determination of A1 and V. By anion-exchange chromatography in a mixed solvent system the separation of Lu, Yb and Tb for neutron-activation analysis was possible ). Lu and Yb were eluted in the same fraction, while Tb was obtained in a separate fraction. 

Since the charges on oxygen are —0.9 electron and on the i/t50-carbon Ci -1-0.5 electron, the dipolar forms are also expected to contribute significantly to the electronic structure of the anion. A certain similarity exists between the phenolate and enolate anions regarding the C—O distances. Quantum chemical calculations" of vibrational frequencies for free PhO in the ground state did show some discrepancies with experimental data3 5.366 frequencies determined using DFT methods compare reasonably... 

A dynamic method called Hittorf s method allows determining transport numbers under migration, a method comparable with a fuel cell under operation. The two compartments in the cell are separated by an ion exchange membrane and both compartments are filled with the same KOH solution (same concentration). A current is applied between the two electrodes on either side of the compartments. At the cathode, hydrogen and hydroxide are produced, while at the anode hydroxide is consumed and oxygen is produced. To maintain electroneutrality, the cations (K" ) and anions (OH ) present in the solution migrate through the membrane from one compartment to the other. Anionic and cationic transport numbers f and f ) can subsequently be determined [20,205,206] ... 

Sensitivity of the proposed method correlates with molai absorptivity of the cyanine dye. Mixed POMs PMeMo O j (Me=TP+, Sb +, BP+) were chosen as analytical form because of its higher stability as compared with 12-molybdophosphate. Only 2-3T0 concentration of molybdate is enough for complete formation of POM avoiding in this way formation of lA with polymolybdate ions. In addition, mixed POMs are stable in wider interval of pH. Increasing of anion chai ge from 3 to 5(6) is also favorable. Constant absorbance of lA is observed in the acidity range of 0.12-0.28 M. 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

The condensation of nitro compounds and imines, the so-called aza-Henry or nitro-Mannich reaction, has recently emerged as a powerful tool for the enantioselective synthesis of 1,2-diamines through the intermediate /3-amino nitro compounds. The method is based on the addition of a nitronate ion (a-nitro carbanion), generated from nitroalkanes, to an imine. The addition of a nitronate ion to an imine is thermodynamically disfavored, so that the presence of a protic species or a Lewis acid is required, to activate the imine and/or to quench the adduct. The acidic medium is compatible with the existence of the nitronate anion, as acetic acid and nitromethane have comparable acidities. Moreover, the products are often unstable, either for the reversibility of the addition or for the possible /3-elimination of the nitro group, and the crude products are generally reduced, avoiding purification to give the desired 1,2-diamines. Hence, the nitronate ion is an equivalent of an a-amino carbanion. 

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