Free solution

Xu X-H and Yeung E S 1997 Direst measurement of singie-moieouie diffusion and photodeoomposition in free solution Science 275 1106-9... 

In water pollution studies, the oxygen content can be measured by making the water alkaline and shaking a measured volume with an oxygen-free solution containing Mn- (aq). The solution is acidified with sulphuric acid, potassium iodide added and the liberated iodine titrated with sodium thiosulphate. 

Solid NaOH is always contaminated with carbonate due to its contact with the atmosphere and cannot be used to prepare carbonate-free solutions of NaOH. Solutions of carbonate-free NaOH can be prepared from 50% w/v NaOH since Na2C03 is very insoluble in concentrated NaOH. When CO2 is absorbed, Na2C03... 

A value for the molecular weight which is low by a factor z + 1 is obtained for salt-free solutions if the experimental results are analyzed as if the polymer were uncharged. 

This carbon dioxide-free solution is usually treated in an external, weU-agitated liming tank called a "prelimer." Then the ammonium chloride reacts with milk of lime and the resultant ammonia gas is vented back to the distiller. Hot calcium chloride solution, containing residual ammonia in the form of ammonium hydroxide, flows back to a lower section of the distiller. Low pressure steam sweeps practically all of the ammonia out of the limed solution. The final solution, known as "distiller waste," contains calcium chloride, unreacted sodium chloride, and excess lime. It is diluted by the condensed steam and the water in which the lime was conveyed to the reaction. Distiller waste also contains inert soHds brought in with the lime. In some plants, calcium chloride [10045-52-4], CaCl, is recovered from part of this solution. Close control of the distillation process is requited in order to thoroughly strip carbon dioxide, avoid waste of lime, and achieve nearly complete ammonia recovery. The hot (56°C) mixture of wet ammonia and carbon dioxide leaving the top of the distiller is cooled to remove water vapor before being sent back to the ammonia absorber. 

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

Carbonates. Iron(II) carbonate [563-71-3] FeCO, precipitates as a white soHd when air-free solutions of alkah metal carbonates and iron(II) salts are mixed. The limited tendency of [Fe(H20)g] to hydroly2e is illustrated by the lack of carbon dioxide evolution in this reaction. The soHd rapidly... 

C. It can be obtained from its hahde-free solutions in cyclohexane and ethylether by vacuum distUlation to remove the ether. The usual preparative method is by reaction of chloro- or bromobenzene and lithium metal in ethyl ether or in a mixture of ethyl ether and cyclohexane. 

Isopiestic or isothermal distillation. This technique can be useful for the preparation of metal-free solutions of volatile acids and bases for use in trace metal studies. The procedure involves placing two beakers, one of distilled water and the other of a solution of the material to be purified, in a desiccator. The desiccator is sealed and left to stand at room temperature for several days. The volatile components distribute themselves between the two beakers whereas the non-volatile contaminants remain in the original beaker. This technique has afforded metal-free pure solutions of ammonia, hydrochloric acid and hydrogen fluoride. 

If an alcohol-free solution of diazomcthane is required, absolute ether should be used throughout this preparation. 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Generally, electrophoresis is carried out not in free solution but in a porous support matrix such as polyacrylamide or agarose, which retards the movement of molecules according to their dimensions relative to the size of the pores in the matrix. 

Chloride-free solutions (up to 5 M concentration) can be made by treating CI2O with water at 0° or industrially by passing CI2O gas into water. In fact, concentrated solutions of HOCl also contain appreciable amounts of CI2O which can form a... 

P. D. Grossman, J. C. Colburn, H. H. Lauer, R. G. Nielsen, R. M. Riggin, G. S. Sittampalam and E. C. Rickard, Application of free-solution capillary electrophoresis to the analytical scale separation of proteins and peptides . Anal. Chem. 61 1186-1194 (1989). 

An alcohol-free solution of diazomethane in ether is prepared as in Chapter 17, Section III. This solution is approximately 0.5 M in diazomethane and may be standardized by titration as follows benzoic acid (0.6 g, approx. 0.005 mole) is weighed accurately into an Erlenmeyer flask and suspended in 5 ml of ether. The diazomethane solution (approx. 5 ml) is added from a buret with swirling, care being taken that an excess of unreacted benzoic acid remains (the yellow color of the diazomethane should be completely discharged). The excess benzoic acid is now titrated with standard 0.2 N sodium hydroxide solution, and the concentration of diazomethane is calculated. 

The process employed in carrying out this invention is as follows A mixture of 1 to IJ parts acetone (45 kg.), 1 part of lemon-giass oil (38 kg.), IJ to 2 parts of alcohol (75 kg.), 1 to 2 parts of a concentrated lime-free solution of chloride of lime (75 kg.), to which is added a little cobaJtous nitrate (30 gr.) dissolved in water, is boiled during six to eighteen hours at a temperature of 70° to 80° C. in a reflux cooling apparatus. 

When an electric field is imposed perpendicular to the flow, differential interaction between the various solutes and the electric field produce a lateral displacement of individual analyte streams between the two electrodes (Fig. 11-5). Thus, the separations are accomplished in free solution. Individual fractions are collected through an array of closely spaced ports evenly placed across the other end of the chamber. 

As in CE, changing system variables (e.g., pH, ionic strength, additive concentration) is very easy in any of the continuous free flow electrophoresis systems reported here because all the interactions take place in free solution. Indeed, changing system variables may be easier in continuous free flow electrophoresis systems than in a CE system because there are essentially no wall effects. Of course, changing system variables in the continuous free flow electrophoresis apparatus may also be easier... 

The situation will of course be different if the potential is maintained constant, e.g. in cathodic protection. For example, if the potential was maintained constant at, say, E , in an oxygen-free solution the rate due to the h.e.r. would be rq which would be unaffected if the solution was then aerated. However, since the corrosion rate would then increase, the current required to maintain the potential constant would have to be increased. 

Fig. 1.56(a) E-i curves and experimental potential-pH diagram for Armco iron in chloride-free solutions of different pHs (A is the unpolarised potential and P the passivation potential) and (b) E—i curves and experimental potential-pH diagram for Armco iron in solutions of different pHs containing 10 mol dm of chloride ion (r is the rupture potential and p the protection potential). (After Pourbaix )... 

Temperature is the most important of the factors affecting pickle activity. In general, an increase of 10°C causes an increase in pickling speed of about 70 Vo. Agitation of the pickle increases the speed since it assists the removal of the insoluble scale and rapidly renews the acid at the scale surface. Increase in acid concentration up to about 40 Vo w/w in ferrous sulphate-free solutions, and up to lower concentrations in solutions containing ferrous sulphate, increases the activity. Increase in the ferrous sulphate content at low acid concentrations reduces the activity, but at 90-95 C and at acid concentrations of about 30 Vo w/w it has no effect. 

The precipitated precursor can be dissolved and re-crystallized from fluorine-free solutions. This provides excellent conditions for deep purification of the material and reduction of problematic impurities such as titanium, fluorine, etc. Peroxometalates decompose at relatively low temperatures forming tantalum or niobium oxides containing small amount of absorbed water. The absorbed water separation is achieved by further thermal treatment - drying and calcination - of the product ... 

These findings can be attributed to the increase in the local concentration of MV2+ on the APh-x molecular surface caused by eletrostatic interactions. In contrast, the quenching constants for MV2 + and SPV show no such large difference in the SDS micellar and AM systems. The addition of NaCl reduces the value of kq to about one-third that for the quenching of APh-9 (APh-x with 9 mol% Phen units) by MV2 + in a salt-free solution. This effect is mainly accounted for by the screening of electrostatic attraction between APh-9 and MV2+. 

FIGURE 4-15 Cyclic voltanmiograms for 1.5 x 10 3 M ribose (a), glucose (b), galactose (c), and fructose (d) recorded at a Ru02-modified carbon-paste electrode. Dotted lines were obtained in carbohydrate-free solutions. (Reproduced with permission from reference 50.)... 

However, alcohol-free solutions of diazomethane146 must be used to avoid destruction of the intermediate sulfene and a stronger base such as 1,5-diazabicyclo [4.3.0] non-5-ene is required for the final dehydrohalogenation step to obtain sulfones 19a,d. 

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