Concentration from aqueous solutions

The mobile phases that are most effective for use with reverse phases are aqueous mixtures of methanol or acetonitrile and for subtle adjustments, ternary mixtures of water, methanol and acetonitrile or tetrahydrofuran can be used. The greater the water content the more the solutes with dispersive groups will be retained and in fact, in pure water, many substances are irreversibly held on a reverse phase. As already discussed, this characteristic make reverse phases very useful for solute extraction and concentration from aqueous solutions prior to analysis. 

Acidic pesticides and metabolites were concentrated from aqueous solution by the anion procedure of Richard and Fritz (10). The anionic materials in these concentrates were methylated using diazomethane and the derivatized products were separated and detected by gas chromatography. Test results of the recovery efficiencies by this method for several pesticides and suspected metabolites have been reported elsewhere (11). An overall recovery of 93% was achieved for sixteen acidic pesticides and metabolites spiked into water at 200 ppb. 

Dissolved inorganic solids have been shown to inhibit organic recovery eflBciency by freeze concentration from aqueous solution (4). Similarly, increased salt content reduces cationic recovery (Figure 7). As ionic concentration increases at the interface, there is an increase in tendency toward dendritic growth and associated entrapment, changes in surface tension and induced interfacial potential, and impedance of specific ionic migration. 

Zhan, X., Li, J.D., Huang, J.Q. and Chen, C.X. 2009b. Pervaporation properties of PDMS membranes cured with different cross-linking reagents for ethanol concentration from aqueous solutions. 27(4) 533-542. 

Magaldrate is prepared by precipitation from aqueous solutions of sodium or potassium aluminate and a magnesium salt under controlled conditions of concentration and temperature. The precipitated product is collected by filtration, washed to remove soluble by-products, and dried. 

Physical Properties. When crystaUized from aqueous solutions above 5°C, natural (R-R, R )-tartaric acid is obtained in the anhydrous form. Below 5°C, tartaric acid forms a monohydrate which is unstable at room temperature. The optical rotation of an aqueous solution varies with concentration. It is stable in air and racemizes with great ease on heating. Some of the physical properties of (R-R, R )-tartaric acid are Hsted in Table 7. 

Eatty amine oxides are most frequendy prepared from alkyldimethylarnines by reaction with hydrogen peroxide. Aqueous 2-propanol is used as solvent to prepare amine oxides at concentrations of 50—60%. With water only as a solvent, amine oxides can only be prepared at lower concentrations because aqueous solutions are very viscous. Eatty amine oxides are weak cationic surfactants. 

Abbreviations of prominent use properties of the various classes of commercial surfactants are shown in Table 1. Antimicrobial activity includes germicidal, bactericidal, and bacteriostatic effects emolliency describes lubrication or a soft feel imparted to skin by surfactants a hair conditioner is a substantive surfactant appHed from aqueous solution to impart a lubricating or antistatic effect and opacifters are used to thicken hand-dishwashing products and cosmetic preparations to convey an appearance of high concentration and to retard solvent drainage from foam. 

Thiosulfuric Acid. Thiosulfuiic acid [14921 -76-7] is relatively unstable and thus cannot be recovered from aqueous solutions. In laboratory preparation, a lead thiosulfate [26265-65-6] solution is treated with H2S to precipitate PbS, or a concentrated solution of sodium thiosulfate [7772-98-7] is treated with HCl and cooled to — 10°C to crystalline NaCl. Aqueous solutions of thiosulfuric acid spontaneously decompose to yield sulfur, SO2, and polythionic acids, H2S O. Thiosulfuric acid is a strong acid comparable to sulfuric acid. Dissociation constants, = 0.25, = 0.018, have been... 

BeryUium chloride [7787-47-5], BeCl2, is prepared by heating a mixture of beryUium oxide and carbon in chloride at 600—800°C. At pressures of 2.7—6.7 Pa (0.02—0.05 mm Hg) beryllium chloride sublimes at 350—380°C. It is easily hydrolyzed by water vapor or in aqueous solutions. BeryUium chloride hydrate [14871-75-1] has been obtained by concentrating a saturated aqueous solution of the chloride in a stream of hydrogen chloride. ChloroberyUate compounds have not been isolated from aqueous solutions, but they have been isolated from anhydrous fused salt mixtures. 

Hydrometallurigcal Processes. In hydrometaHurgical processes, metal values and by-products are recovered from aqueous solution by chemical or electrolytic processes. Values are solubilized by treating waste, ore, or concentrates. Leaching of copper ores in place by rain or natural streams and the subsequent recovery of copper from mnoff mine water as impure cement copper have been practiced since Roman times. Most hydrometaHurgical treatments have been appHed to ores or overburden in which the copper was present as oxide, mixed oxide—sulfide, or native copper. PyrometaHurgical and hydrometaHurgical processes are compared in Reference 34. 

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. 

Sodium trimetaphosphate was used as an eluting agent for the removal of heavy metals such as Pb, Cd, Co, Cu, Fe, Ni, Zn and Cr from aqueous solutions. Distribution coefficients of these elements have been determined regarding five different concentrations of sodium trimeta phosphate (3T0 M 5T0 M 0.01 M 0.05 M 0.1 M) on this resin. By considering these distribution coefficients, the separation of heavy metals has been performed using a concentration gradient of 3T0 - 5T0 M sodium trimetaphosphate. Qualitative and quantitative determinations were realized by ICP-AES. 

It has been seen that this resin has also some important advantages over the other resins in the literature like high total ion exchange capacity, easy synthesis, lower cost, simple regeneration. Furthermore, very good sepai ations were obtained using a concentration gradient of elution. In these elutions, very low concentrations of sodium trimetaphosphate were used. As a result, the resin synthesized can be used as an adsorbent for the effective removal of Pb, Cd, Co, Cu, Fe, Ni, Zn and Cr from aqueous solutions. 

Ferric nitrate (9H2O) [7782-61-8] M 404.0, m 47°(dec). Cryst from aqueous solutions of moderately strong HNO3 as the violet nonahydrate. With more concentrated aqueous solns (containing some HNO3), the hexahydrate crysts out. The anhydrous salt is slightly deliquescent and decomposes at 47°. 

Sodium 2,2, 4-trihydroxyazobenzene-5 -sulfonate [3564-26-9] M 295.3. Purified by precipitating the free acid from aqueous solution using concentrated HCl, then washing and extracting with EtOH in a Soxhlet extractor. Evaporation of the EtOH left the purified acid. 

As Fig. 16 shows, the preferential binding of DMSO, DMF and NMF from aqueous solution to (Lys HBr)n at low contents of the organic solvent x increases with its concentration. However, at approximately x3 = 0,2 a maximum is reached and then preferential hydration between x3 = 0,3 and 0,5 occurs. No preferential binding was observed for NMP, EG or 2 PrOH, however increasing hydration occured with x3. Only in 2 PrOH at x3 > 0,3 a-helix formation occured. Furthermore binding parameters for the systems NMP + DMSO, EG + DMSO and DMF + DMSO have been determined. An initial preferential binding of DMSO by (Lys HBr)n, a maximum and a subsequently inversion of the binding parameter was also observed in these mixtures. The order of relative affinity is DMSO > DMF > EG > NMP. In DMF/DMSO-mixtures (Lys HBr) attains an a-helical conformation above 20 vol.- % DMF and in 2-PrOH/water above 70 vol.- % 2 Pr-OH. 

Fabiato, A. (1988). Computer programs for calculating total from specified free or free from specified total ionic concentrations in aqueous solutions containing multiple metals and ligands. Method. Enzymol. 157 378-417. 

Fig. 11. Change of the fluorescence spectra of polyfpropynoic acid)s as a result of transfer from solution [(1) PPAL, (2) PPASJ to the solid phase [(3) PPAL, (4) PPASJ. Concentration of aqueous solutions 10 4 mol/1. The fluorescence spectra of the samples in solid phase were taken from powdered polymers placed between two quartz plates. Slit width 0.2 mm sensitivity 3,0 excitation = 365 nm. / = intensity...

Much of the earth s surface is water, and an important aspect of the volatilization of pollutants is their movement from water to air. The movement of solutes between water and air is governed by Henry s law, which states that at equilibrium, the concentration of a chemical in the vapor state bears a constant relationship to the concentration in aqueous solution. 

The hydronium ion concentration in aqueous solution ranges from extremely high to extremely low. Here are three... 

Electrodeposition of antimony sesquitelluride, Sb2Tc3, or of (Bii xSbx)2Te3 alloys from aqueous solutions is challenging because it is difficult to achieve a sufficiently high concentration of antimony. Complexing agents such as tartaric acid, citric acid, or FUTA have been used to solubilize Sb in water. 

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