Pseudo-solution

For cases B and C, Robbins ( Liquid-Liquid Extraction, in Schweitzer, Handbook of Separation Techniques for Chemical Engineers, McGraw-Hill, New York, 1979, sec. 1.9) developed the concept of pseudo solute concentrations for the feed and solvent streams entering the extractor that will allow the Kremser equations to be used. 

The silica dispersion showed the smallest retention volume. It should be noted, however, that the authors reported that the silica dispersion required sonicating for 5 hours before the silica was sufficiently dispersed to be used as "pseudo-solute". The retention volume of the silica dispersion gave the value of the kinetic dead volume, /.e., the volume of the moving portion of the mobile phase. It is clear that the difference between the retention volume of sodium nitroprusside and that of the silica dispersion is very small, and so the sodium nitroprusside can be used to measure the kinetic dead volume of a packed column. From such data, the mean kinetic linear velocity and the kinetic capacity ratio can be calculated for use with the Van Deemter equation [12] or the Golay equation [13]. 

Pseudo-Idsung, /. pseudo solution, -merie, / pseudomerism. 

Colloidal Dispersions or Solutions (Sols) and Colloids. Colloidal solutions (or rather "pseudo solutions ), also called sols (or in case of liquids hydrosols) are heterogeneous systems consisting of a "dispersion medium (mostly a liquid) and a "dispersed or "suspended medium known as a "colloid . Colloidal particles are invisible under ordinary microscope but detectable by the ultramicroscope. Their size ranges from ca 1 x 10 7 to 1 x 5 smm. If the dispersion is a viscous, sticky, transparent liquid, it is what is generally known as a "colloidal solution . As examples of this may be cited a soln of gum-arabic in water and sol ns of NC in acetone, ethyl acetate or ether alcohol. When "solns are dialized, most of the colloidal particles do not pass thru the membrane. This is their principal distinction from "crystalloids , which are substances like Na chloride, etc. If part of the volatile liquid (dispersing medium), is evaporated the resulting tacky, jellylike substance is known as a gel. 

Procedure B. A variant of the method consists in precontacting monomer and rubber in the absence of water and subsequently dispersing the pseudo-solution obtained in an aqueous solution of poly (vinyl alcohol) containing the initiator in suspension. 

Most NMR measurements are carried out in solution, where rapid molecular motion removes the effects of chemical shift anisotropy and (generally) produces sharp lines. For the study of solids, techniques are used which combine rapid spinning about the magic angle axis with special pulses, which remove much of the anisotropy and produce pseudo-solution spectra. 

One other application where Nano-probe technology excels relative to conventional tube or flow NMR probe formats is in the area of heterogeneous samples. One of the early applications demonstrated for the Nano-probe was the acquisition of NMR spectral data for chemically modified polymer beads used in solid-phase-assisted peptide synthesis and related chemical transformations.21 23 When chemically modified beads are interrogated in a conventional NMR sample tube, the resin bead behaves as an insoluble material and at best very broad and poorly resolved spectra may be recorded. In contrast, when the same beads are placed in a Nano-probe and spun at several kHz at the magic angle, there is sufficient solvation of the pendant chemical moiety and the linker to resin bead nucleus to allow the modified portion to behave as if it is in pseudo solution, which allows reasonable NMR spectra to be recorded. Various factors affect the quality of the NMR data that can be obtained for the pendant molecule, which include the tether length and the solvent used for the measurement.23 There have been a diverse assortment of applications of Nano-probe applications reported in the literature that are discussed in further detail in Section 6.3. 

Note that the normal system can be obtained formally by multiplication of the original system (3.2) by the transposed matrix AT. However, in general cases, the pseudosolution mo is not equivalent to the solution of the original system, because the new system described by equation (3.8) is not equivalent to the original system (3.2) if matrix A is not square. The main characteristic of the pseudo-solution is that it provides the minimum of the misfit functional. 

To find a pseudo-solution numerically, we can apply the method of singular value decomposition (E.13) and obtain... 

Expression (3.12) gives directly the pseudo-solution of the system (3.4). 

Instead of passage of gas bubbles through the solution, the aqueous pseudo-solution can be shaken with non-polar solvent. In such cases, hydrophobic sparingly soluble compounds accumulate at the phase boundary or adhere to the wall of the separating funnel used. After careful removal of both liquid phases, and washing, the precipitate adhering to the wall can be dissolved in a polar solvent and the isolated trace elements can be determined. 

With metal ions, some organic reagents form coloured compounds that are sparingly soluble both in water and in organic solvents. They are either polynuclear complexes, such as formed by phenylfluoron with Sn(IV) or with Ge(IV), or adsorption-type compounds such as those formed by titanium yellow with Mg. In such cases, the absorbance is measured for suspensions of coloured pseudo-solutions stabilized with protective colloids [e.g., gum arabic, gelatine, poly(vinyl alcohol)]. 

Aluminon (ammonium aurintricarboxylate) (formula 6.1) was formerly an important reagent for aluminium (e 2-10 ) [4,31,43]. It forms a sparingly soluble red chelate with A1 ions in acetate buffer. Protective colloids (e.g., gelatine) are necessary to stabilize the pseudo-solution. 

The addition of an aqueous solution of sodium diethyidithiocarbamate (Na-DDTC, cupral) (formula, 4.40) to a solution (at pH 4-11) containing small amounts of copper(II) ions produces a yellow-brown colour owing to a colloidal suspension of the sparingly-soluble copper 1 2 chelate with DDTC. The reagent co-ordinates with copper through the two sulphur atoms to form a chelate with four-membered rings, which is a rather rare configuration. Protective colloids (e.g., gum arabic) stabilize the pseudo-solution, and permit the spectrophotometric determination of copper. Cu (11) has been determined in aqueous solutions in the presence of surfactants [17],... 

Sensitive methods for lead include a number based on ion-associates formed by the anionic iodide-lead complex and the basic dyes, such as Malachite Green (benzene, e = 8.0-10 ) (58,59], Brilliant Green (59], Ethyl Violet [59], fuchsin (formula 27.1) (extraction with benzene-cyclohexane from 0.2 M H2SO4, e = 2.0-10 at 560 nm [60], and cyanine dyes [61]. In the method involving the antipyiine dye Chrompyrazole I (formula 23.1), the pseudo-solution formed is stabilized with the non-ionic surfactant OP-10 [62]. 

The molar absorptivity of the pseudo-solution of the magnesium compound with Titan Yellow is 3.6-10 at 545 (a = 1.5). The intensity and reproducibility of the colour obtained are affected by the method of pH adjustment, the excess of Titan Yellow, the protective colloid used, the temperature of the solution, and the time of standing. Immediately after the start of the colour reaction, an increase in absorbance is noticed, but after 10-30 min the colour of the solution remains almost constant. After this it weakens progressively. Hydroxylamine is reported to stabilize the colour [12]. 

Niobium (Nb, at. mass 92.91) hydrolyses (in the absence of complexing anions) over the pH range 0-14. Polymerized forms of Nb(V) give pseudo-solutions or they separate as a white precipitate. When fused with NaOH, Nb20s forms the niobate, which is soluble in NaOH solutions. Niobium(V) forms stable fluoride, tartrate, oxalate, and peroxide complexes. The niobium complexes are more stable than the corresponding Ta complexes. A niobium chloride complex is formed in >5 M HCl solutions. Niobium(V) can be reduced to coloured species of Nb(III) and Nb(IV). In an acid medium, zinc metal reduces Nb(V), but not Ta(V). 

On being heated in acid solutions (or pseudo-solutions), niobium and tantalum hydrolyse and coagulate to form hydrous oxides. The following compounds may be used as collectors for traces of niobium or tantalum Zr(OH)4 and Mn02aq. in acid solutions, and Fe(OH)3 and Mg(OH)2 in alkaline solutions. When an alkaline melt (Na2C03, NaOH) is leached, Nb and Ta remain in the solid phase, while W, Mo, V, and Re pass into the aqueous solution [1]. 

Place the clear, colourless, neutral solution, containing not more than 50 pg of NH3, in a 25-ml standard flask, add 1 ml of the tartrate solution, 1 ml of 1 % gum arabic solution, and 1 ml of Nessler s reagent, and dilute the solution to the mark with water. After 10 min, measure the absorbance of the pseudo-solution at 400 nm, using a reagent blank solution as reference. 

The colour reaction is carried out in 0.1 M HCl, and the time necessary for colour development in the aqueous pseudo-solution is 50 min. In the extractive spectrophotometric method [36], the time for reaction at pH 2-3 (in the presence of formic acid) is 30 min, after which the solution is neutralized to pH 6-7, and the piazselenol is extracted into toluene. The colour reaction may be accelerated by heating the solution. Within the pH range 5-10, the distribution coefficient of piazselenol between toluene and water is high, and one portion of toluene extracts practically all the selenium complex into the organic phase. The free reagent (DAB) is also extracted. Related solvents such as benzene and xylene may be substituted for toluene. 

Tin(II) chloride, ascorbic acid, thiourea, or hydrazine are used to reduce selenium(IV). In 3-4 M HCl solutions, SnCh rapidly reduces Se(FV) in the cold. Depending on the reducing agent and acid strength, pseudo-solutions of different colour are obtained. 

Determination of Se. To the sample solution (in -3 M HCl) containing not more than 0.5 mg of Se in a volume of 15 ml, add 3 ml of poly(vinyl alcohol) solution, and mix well. Add 1.0 ml of the SnCl2 solution with stirring. Measure the absorbance of the coloured pseudo-solution at 400 nm, vi. water as the reference. 

Sensitive extraction-spectrophotometric methods are based on the extractable (into CHCI3, 1,2-diehloroethane, benzene, or toluene) ion-associates of basic dyes and anionic Ag complexes with cyanide [35,36], iodide [37,38], and bromide [39]. In these methods, use has been made of such dyes as Crystal Violet [35,39], Brilliant Green [38,39], Malachite Green [39], Methylene Blue [36], and Nile Blue A [37]. In some of these methods the molar absorptivities are elose to MO [36,39]. A flotation method has been proposed, based on the addition compound [R6G ][Ag(SCN )2] [R6G ][SCN ] which is formed by silver ions (at pH 2-5) in the presence of thiocyanate and Rhodamine 6G (flotation with DIPE, the precipitated compound is washed and dissolved in acetone, e = 1.5-10 ) [40]. The complex Ag(CN)2 , associated with Crystal Violet, has been utilized in another flotation-spectrophotometric method of determining silver [41]. Silver has been determined also in a system comprising thiocyanate and Rhodamine B, as an aqueous pseudo-solution, in the presence of poly(vinyl alcohol) [42]. 

Tin(IV) reacts with phenylfluorone (formula 22.1) in aeidic medium to form a sparingly soluble complex. At low coneentrations of tin, this complex oecurs in solution as a sol suitable for the spectrophotometric determination of tin [11,24,25]. The reagent solution is yellow, whereas the pseudo-solution of the Sn-phenylfluorone complex is orange-red. 

The molar absorptivity of the pseudo-solution is 7.7-10" at 510 nm (sp. abs. 0.65). The method is of low selectivity. Numerous multivalent metals (e.g., Sb, Ge, Zr, Ga, Fe, Mo, and Ti) interfere. Small amounts of Ti, and Mo can be masked with hydrogen peroxide. Antimony, which often accompanies tin, can be masked with citric acid. 

Some sensitive methods for determining uranium are based on ion-associates consisting of anionic uranium(VI) complexes and basic dyes such as Brilliant Green and Crystal Violet [118], Rhodamine B [119], Butylrhodamine B [120], Malachite Green [ 121], Brilliant Green [122,123]. In the methods based on anthranilic acid with Rhodamine 6G [124], or thiocyanate with Rhodamine B [125] the associates formed are not extracted, but the absorbance is measured for aqueous pseudo-solutions, protected with gelatine or poly(vinyl alcohol). 

Alizarin S (Alizarin Red S, formula 57.1) reacts with Zr (HO ions in acid medium (pH 0.5-1.0) to form a purple-red compound which is sparingly soluble in water. In the presence of a protective colloid, it forms a pseudo-solution. The reagent is soluble in water to give a yellow colour. In the spectrophotometric method for determining Zr [44-46] the colour reaction is carried out in 0.1-0.2 M HCl, HNO3 or HCIO4. In such media, the effect of other... 

The general case was earlier treated [79] as a convergent series expansion of the analytical pseudo-solution from the differential equation ... 

Pitch is a "pseudo solution" of a wide variety of different generic classes of hydrocarbons ranging from paraffins at one extreme to very highly aromatic species at the other. By using the Theory of Solubility for Non-Electrolytes, specific fractions can be isolated from a pitch by properly selecting a solvent system and extraction conditions. "Tailored" precursors for carbon fiber and other carbon products, such as carbon/carbon matrices and bulk graphites, can thus be obtained. The technique of extraction, the characteristics of different precursors, and the structure and properties of carbon fiber and composites made from solvent extracted precursors will be discussed. 

Sometimes SHH XS finds two groups of potential solutions, where one corresponds only to a pseudo-solution. If this pseudo-solution has the lower combined figure of merit of the two, the program will chose it over the correct solution. In such a case it is common practice to examine the SHELXS. 1st file, identify the odier possible solution and run the program a second time specifying die seminvariants in the TREF command. This book is about structure refinement, not die solution of die phase problem and for furdier details die reader is referred to the SHELX manual or the original publication (Sheldrick, 1990). 

Viscosity measurements on dilute polymer pseudo-solutions can be used to determine the molecular weight of the dissolved polymer. If polymer concentrations are restricted to levels that give a solution viscosity no more that 1.5 times the solvent viscosity, then the viscosity versus concentration plot determined by measurements on a group of polymer pseudo-solutions can be used with the Huggins (15a.), Krammerer(15b.), Schulz-Blaschka(15c), or Martin (15d.) equations to determine the limiting viscosity number of the polymer, [ ]. 

Viscosity measurements on dilute polymer pseudo- solutions can be used to determine the molecular weight of the dissolved polymer. The uniform dispersal of polymer molecules in solvent is ealled a pseudo-solution beeause polymer molecules are so large that cubic nanometer volumes in the fluid that contain a polymer molecule are decidedly different than equal volumes of the fluid that do not contain a polymer. A fluid that has dissolved a polymer is therefore not isotropic and is not a true solution. 

The larger the difference between polymer and solvent interaction parameters, the smaller the chanceof polymer pseudo-solution foimation. A collection of solvents, solubility parameters, and polymer solubility parameters for polymers covered by this book are given in Table 8. 

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